Search results
Search for "skeletal rearrangement" in Full Text gives 18 result(s) in Beilstein Journal of Organic Chemistry.
Oxetanes: formation, reactivity and total syntheses of natural products
- Peter Gabko,
- Martin Kalník and
- Maroš Bella
Beilstein J. Org. Chem. 2025, 21, 1324–1373, doi:10.3762/bjoc.21.101
Graphical Abstract
Figure 1: Bond lengths and bond angles in oxetane at 140 K [2].
Figure 2: Analogy of 3-substituted oxetanes to carbonyl and gem-dimethyl groups [12].
Figure 3: Use of oxetanes in drug design – selected examples.
Figure 4: Examples of oxetane-containing natural products.
Scheme 1: Synthetic strategies towards construction of the oxetane ring.
Scheme 2: Overview of intramolecular Williamson etherification and competing Grob fragmentation.
Scheme 3: Synthesis of spiro-oxetanes via 1,4-C–H insertion and Williamson etherification.
Scheme 4: Use of phenyl vinyl selenone in the synthesis of spirooxindole oxetanes.
Scheme 5: Synthesis of bicyclic 3,5-anhydrofuranoses via double epoxide opening/etherification.
Scheme 6: Preparation of spirooxetanes by cycloisomerisation via MHAT/RPC.
Scheme 7: Oxetane synthesis via alcohol C–H functionalisation.
Scheme 8: Access to oxetanes 38 from α-acetyloxy iodides.
Scheme 9: The kilogram-scale synthesis of oxetane intermediate 41.
Scheme 10: Overview of the intramolecular opening of 3-membered rings.
Scheme 11: Synthesis of 4,7-dioxatricyclo[3.2.1.03,6]octane skeletons.
Scheme 12: Silicon-directed electrophilic cyclisation of homoallylic alcohols.
Scheme 13: Hydrosilylation–iodocyclisation of homopropargylic alcohols.
Scheme 14: Cu-catalysed intramolecular O-vinylation of γ-bromohomoallylic alcohols.
Scheme 15: Cu-catalysed intramolecular cross-coupling of hydroxyvinylstannanes.
Scheme 16: Isomerisation of oxiranyl ethers containing weakly carbanion-stabilising groups.
Scheme 17: Cyclisation of diethyl haloalkoxymalonates.
Scheme 18: Synthesis of oxetanes through a 1,5-HAT/radical recombination sequence.
Scheme 19: General approach to oxetanes via [2 + 2] cycloadditions.
Scheme 20: Synthesis of tricyclic 4:4:4 oxetanes through a photochemical triple cascade reaction.
Scheme 21: Iridium-catalysed Paternò–Büchi reaction between α-ketoesters and simple alkenes.
Scheme 22: Three-step synthesis of spirocyclic oxetanes 83 via Paternò–Büchi reaction, nucleophilic ring openi...
Scheme 23: Enantioselective Paternò–Büchi reaction catalysed by a chiral iridium photocatalyst.
Scheme 24: Synthesis of polysubstituted oxetanes 92 via Cu(II)-mediated formal [2 + 2] cycloadditions.
Scheme 25: Synthesis of alkylideneoxetanes via NHC- and DBU-mediated formal [2 + 2] cycloadditions.
Scheme 26: Use of sulphur-stabilised carbanions in ring expansions.
Scheme 27: Synthesis of α,α-difluoro(arylthio)methyl oxetanes.
Scheme 28: Ring expansion in an industrial synthesis of PF-06878031.
Scheme 29: Ring contraction of triflated 2-hydroxy-γ-lactones.
Scheme 30: Ring contraction in an industrial synthesis of PF-06878031.
Scheme 31: Photochemical ring contraction of 2,5-dihydrofurans by aryldiazoacetic acid esters.
Scheme 32: Synthesis of 3-oxetanones via O-H insertion of carbenes.
Scheme 33: Synthesis of phosphonate oxetanones via gold-mediated alkyne oxidation/O–H insertion.
Scheme 34: Syntheses and common derivatisations of 3-oxetanone.
Scheme 35: SN1 substitution of 3-aryloxetan-3-ols by thiols and alcohols.
Scheme 36: Fe–Ni dual-catalytic olefin hydroarylation towards 3-alkyl-3-(hetero)aryloxetanes.
Scheme 37: Synthesis of 3-aryloxetan-3-carboxylic acids.
Scheme 38: Decarboxylative alkylation of 3-aryloxetan-3-carboxylic acids.
Scheme 39: Synthesis of 3-amino-3-aryloxetanes via photoredox/nickel cross-coupling catalysis.
Scheme 40: Intermolecular cross-selective [2 + 2] photocycloaddition towards spirooxetanes.
Scheme 41: Synthesis of 3-aryl-3-aminooxetanes via defluorosulphonylative coupling.
Scheme 42: Two-step synthesis of amide bioisosteres via benzotriazolyl Mannich adducts 170.
Scheme 43: Functionalisation of oxetanyl trichloroacetimidates 172.
Scheme 44: Synthesis of oxetane-amino esters 176.
Scheme 45: Tandem Friedel–Crafts alkylation/intramolecular ring opening of 3-aryloxetan-3-ols.
Scheme 46: Synthesis of polysubstituted furans and pyrroles.
Scheme 47: Synthesis of oxazolines and bisoxazolines.
Scheme 48: Tandem, one-pot syntheses of various polycyclic heterocycles.
Scheme 49: Synthesis of 1,2-dihydroquinolines via skeletal reorganisation of oxetanes.
Scheme 50: Synthesis of benzoindolines and 2,3-dihydrobenzofurans and their derivatisations.
Scheme 51: Synthesis of polysubstituted 1,4-dioxanes.
Scheme 52: Preparation of various lactones via ring opening of oxetane-carboxylic acids 219.
Scheme 53: Tsuji-Trost allylation/ring opening of 3-aminooxetanes.
Scheme 54: Arylative skeletal rearrangement of 3-vinyloxetan-3-ols to 2,5-dihydrofurans.
Scheme 55: Reductive opening of oxetanes using catalytic Mg–H species.
Scheme 56: Opening of oxetanes by silyl ketene acetals.
Scheme 57: Rhodium-catalysed hydroacylation of oxetanes.
Scheme 58: Generation of radicals from oxetanes mediated by a vitamin B12-derived cobalt catalyst.
Scheme 59: Reductive opening of oxetanes by B–Si frustrated Lewis pairs.
Scheme 60: Zirconocene-mediated reductive opening of oxetanes.
Scheme 61: Enantioselective syntheses of small and medium-size rings using chiral phosphoric acids.
Scheme 62: Asymmetric synthesis of 2,3-dihydrobenzo[b]oxepines catalysed by a chiral scandium complex.
Scheme 63: Enantioselective synthesis of 1,3-bromohydrins under a chiral squaramide catalysis.
Scheme 64: Enantioselective opening of 2-aryl-2-ethynyloxetanes by anilines.
Scheme 65: Ru-catalysed insertion of diazocarbonyls into oxetanes.
Scheme 66: Ring expansion of oxetanes by stabilised carbenes generated under blue light irradiation.
Scheme 67: Expansion of oxetanes via nickel-catalysed insertion of alkynyltrifluoroborates.
Scheme 68: Nickel-catalysed expansion of oxetanes into ε-caprolactones.
Scheme 69: Expansion of oxetanes via cobalt-catalysed carbonyl insertion.
Scheme 70: Gold-catalysed intramolecular 1,1-carboalkoxylation of oxetane-ynamides.
Scheme 71: Expansion of oxetanes by stabilised sulphoxonium ylides.
Scheme 72: Cu-catalysed ring expansion of 2-vinyloxetanes by diazoesters.
Scheme 73: Total synthesis of (+)-oxetin.
Scheme 74: Total synthesis of racemic oxetanocin A.
Scheme 75: Total synthesis of (−)-merrilactone A.
Scheme 76: Total synthesis of (+)-dictyoxetane.
Scheme 77: Total synthesis of ent-dichrocephone B.
Scheme 78: Total synthesis of (−)-mitrephorone A.
Scheme 79: Total synthesis of (−)-taxol.
Recent advances and future challenges in the bottom-up synthesis of azulene-embedded nanographenes
- Bartłomiej Pigulski
Beilstein J. Org. Chem. 2025, 21, 1272–1305, doi:10.3762/bjoc.21.99
- (Scheme 24). Further heating on the Au(111) surface led to products with partial skeletal rearrangement, driven by intramolecular structural strain. Both nanographenes, 186 and 187, contain six formal azulene subunits and exhibit nearly planar geometry. However, theoretical analysis of NICS values
Graphical Abstract
Figure 1: a) Stone–Wales (red) and azulene (blue) defects in graphene; b) azulene and its selected resonance ...
Figure 2: Examples of azulene-embedded 2D allotropic forms of carbon: a) phagraphene and b) TPH-graphene.
Scheme 1: Synthesis of non-alternant isomers of pyrene (2 and 6) using dehydrogenation.
Scheme 2: Synthesis of non-alternant isomer 9 of benzo[a]pyrene and 14 of benzo[a]perylene using dehydrogenat...
Scheme 3: Synthesis of azulene-embedded isomers of benzo[a]pyrene (18 and 22) inspired by Ziegler–Hafner azul...
Figure 3: General strategies leading to azulene-embedded nanographenes: a) construction of azulene moiety in ...
Scheme 4: Synthesis of biradical PAHs possessing significant biradical character using oxidation of partially...
Scheme 5: Synthesis of dicyclohepta[ijkl,uvwx]rubicene (29) and its further modifications.
Scheme 6: Synthesis of warped PAHs with one embedded azulene subunit using Scholl-type oxidation.
Scheme 7: Synthesis of warped PAHs with two embedded azulene subunits using Scholl oxidation.
Scheme 8: Synthesis of azulene-embedded PAHs using [3 + 2] annulation accompanied by ring expansion.
Scheme 9: Synthesis of azulene-embedded isomers of linear acenes using [3 + 2] annulation accompanied by ring...
Scheme 10: Synthesis of azulene-embedded PAHs using intramolecular C–H arylation.
Scheme 11: Synthesis of azulene-embedded isomers of acenes using intramolecular C–H arylation.
Scheme 12: Synthesis of azulene-embedded PAHs using intramolecular condensations.
Scheme 13: Synthesis of azulene-embedded PAH 89 using palladium-catalysed [5 + 2] annulation.
Scheme 14: Synthesis of azulene-embedded PAHs using oxidation of substituents around the azulene core.
Scheme 15: Synthesis of azulene-embedded PAHs using the oxidation of reactive positions 1 and 3 of azulene sub...
Scheme 16: Synthesis of azulene-embedded PAHs using intramolecular C–H arylation.
Scheme 17: Synthesis of an azulene-embedded isomer of terylenebisimide using tandem Suzuki coupling and C–H ar...
Scheme 18: Synthesis of azulene embedded PAHs using a bismuth-catalyzed cyclization of alkenes.
Scheme 19: Synthesis of azulene-embedded nanographenes using intramolecular cyclization of alkynes.
Scheme 20: Synthesis of azulene-embedded graphene nanoribbons and azulene-embedded helicenes using annulation ...
Scheme 21: Synthesis of azulene-fused acenes.
Scheme 22: Synthesis of non-alternant isomer of perylene 172 using Yamamoto-type homocoupling.
Scheme 23: Synthesis of N- and BN-nanographenes with embedded azulene unit(s).
Scheme 24: On-surface synthesis of azulene-embedded nanographenes from benzenoid precursors via dehydrogenatio...
Scheme 25: On-surface synthesis of azulene-embedded nanographenes from benzenoid precursors.
Scheme 26: On-surface synthesis of azulene-embedded nanoribbons.
Chemo-enzymatic total synthesis: current approaches toward the integration of chemical and enzymatic transformations
- Ryo Tanifuji and
- Hiroki Oguri
Beilstein J. Org. Chem. 2024, 20, 1693–1712, doi:10.3762/bjoc.20.151
- hybrid syntheses of cotylenol (1) and brassicicenes [19]. The key oxidative allylic rearrangement was conducted enzymatically, while the skeletal rearrangement originally mediated by P450 enzymes in the biosynthetic pathway was achieved through chemical transformation. Hence, this strategy can be
- of scaffold 6 yield a series of intermediates and natural products, including cotylenol (1) and brassicicenes I and B (9 and 10), as well as brassicicene O (12), which possesses a distinct scaffold resulting from a skeletal rearrangement. To the core scaffold 6, the P450 enzymes, BscB and BscC
- skeletal rearrangement, providing the distinct skeleton of 11 via carbocation C. This rearrangement involves the preferential migration of an alkenyl group in C to the carbocation, followed by deprotonation at C18 to form an exo-olefin. β-face-selective hydroxylation at C12 in 11 by the P450 enzyme BscG
Graphical Abstract
Scheme 1: Targeted natural products and key enzymatic transformations in the chemo-enzymatic total syntheses ...
Scheme 2: Biosynthetic pathway to brassicicenes in Pseudocercospora fijiensis [14]. (A) Cyclization phase catalyz...
Scheme 3: Chemo-enzymatic total synthesis of cotylenol (1) and brassicicenes. (A) Chemical cyclization phase....
Scheme 4: (A) Biosynthetic pathway for trichodimerol (2) in Penicillium chrysogenum. (B) Chemo-enzymatic tota...
Scheme 5: (A) Proposed biosynthetic pathway for chalcomoracin (3) in Morus alba. (B) Outline of the biosynthe...
Scheme 6: (A) Chemo-enzymatically synthesized natural products by using the originally identified MaDA. (B) M...
Scheme 7: Proposed biosynthetic mechanism of tylactone (4) in Streptomyces fradiae.
Scheme 8: (A) Chemical synthesis and cascade enzymatic transformations of cyclization precursors. (B) Late-st...
Scheme 9: Proposed biosynthetic mechanism of saframycin A (5) in Streptomyces lavendulae.
Scheme 10: (A) Chemo-enzymatic total synthesis of saframycin A (5) and jorunnamycin A (103). (B) Chemo-enzymat...
Skeletal rearrangement of 6,8-dioxabicyclo[3.2.1]octan-4-ols promoted by thionyl chloride or Appel conditions
- Martyn Jevric,
- Julian Klepp,
- Johannes Puschnig,
- Oscar Lamb,
- Christopher J. Sumby and
- Ben W. Greatrex
Beilstein J. Org. Chem. 2024, 20, 823–829, doi:10.3762/bjoc.20.74
- 10.3762/bjoc.20.74 Abstract A skeletal rearrangement of a series of 6,8-dioxabicyclo[3.2.1]octan-4-ols has been developed using SOCl2 in the presence of pyridine. An oxygen migration from C5 to C4 was observed when the C4 alcohols were treated with SOCl2/pyridine, giving a 2-chloro-3,8-dioxabicyclo[3.2.1
- the acetal in 3 and 6 to the neighbouring C4-position (Figure 1) [19][20]. A variety of products were reported resulting from fluorination as well as the skeletal rearrangement, with the reaction outcome highly substrate-dependent. A key finding in this work was that the configuration of the alcohol
- skeletal rearrangement (vide infra). Inclusion of the soft-nucleophile allyltrimethylsilane in the reaction of 10b to trap potential oxocarbenium ion intermediates also resulted in a complex mixture. During the isolation of the chloroalkyl ether products 11a–f, it was apparent that hydrolysis occurred
Graphical Abstract
Figure 1: Previous work on migration reactions in 6,8-dioxabicyclooctan-4-ols [18].
Scheme 1: Structures for 10a–c, preparation of 10d–f, and X-ray structure of 10e.
Scheme 2: Rearrangement reactions for 10a–f promoted by SOCl2.
Scheme 3: Reactions of allylic alcohols 15 and 18 with SOCl2.
Scheme 4: Appel reactions of dioxabicyclo[3.2.1]octan-4-ols 10a,e,f and 15.
Scheme 5: Some transformations for the skeletal rearrangement products 11a and 12a and X-ray structure for 24....
Figure 2: Mechanism for the rearrangement of 10, and Newman projection and the X-ray structure of 10d project...
Genome mining of labdane-related diterpenoids: Discovery of the two-enzyme pathway leading to (−)-sandaracopimaradiene in the fungus Arthrinium sacchari
- Fumito Sato,
- Terutaka Sonohara,
- Shunta Fujiki,
- Akihiro Sugawara,
- Yohei Morishita,
- Taro Ozaki and
- Teigo Asai
Beilstein J. Org. Chem. 2024, 20, 714–720, doi:10.3762/bjoc.20.65
- stereoisomers, ent-CPP and syn-CPP. Class II TCs can also generate further structural diversity through hydride shifts, methyl shifts, and/or skeletal rearrangement of the labdadienyl+ diphosphate intermediate which is formed by the initial bicyclization. Following this class II TC-mediated cyclization, class I
Graphical Abstract
Figure 1: LRDs in fungi. A) Chemical structures of representative fungal LRDs. B) Reactions catalyzed by sele...
Figure 2: Sequence analysis of AsPS and AsCPS. A) Biosynthetic gene clusters containing AsCPS and AsPS. B) Do...
Figure 3: GC–MS analysis of the A. oryzae transformant. A) TIC of the extracts obtained from AO-AsGGS/AsCPS/A...
Figure 4: GC–MS analysis of the enzymatic reactions. A) Extracted ion chromatograms (EICs) at m/z 272 of the ...
Figure 5: Characterization of CiCPS-PS. A) GC–MS analysis of the transformant expressing CiCPS-PS and AsGGS. ...
Perspectives on push–pull chromophores derived from click-type [2 + 2] cycloaddition–retroelectrocyclization reactions of electron-rich alkynes and electron-deficient alkenes
- Michio Yamada
Beilstein J. Org. Chem. 2024, 20, 125–154, doi:10.3762/bjoc.20.13
- to posit that the phenyl rings possess a degree of rotational freedom, thereby circumventing steric repulsions. The steric congestion surrounding TCBD moieties can also induce further skeletal rearrangement. For instance, the spatial constraints proximal to the surface of fullerene derivatives lead
Graphical Abstract
Scheme 1: Pathway of the [2 + 2] CA–RE reaction of an electron-rich alkyne with TCNE or TCNQ. EDG = electron-...
Scheme 2: Reaction pathway for DMA-appended acetylene and TCNEO.
Scheme 3: Pathway of the [2 + 2] CA–RE reaction between 1 and DCFs.
Scheme 4: Sequential double [2 + 2] CA–RE reactions between 1 and TCNE.
Scheme 5: Divergent chemical transformation pathways of TCBD 6.
Scheme 6: Synthesis of 12.
Scheme 7: [2 + 2] CA–RE reaction of 1 with 14. TCE = 1,1,2,2-tetrachloroethane.
Scheme 8: Autocatalytic model proposed by Nielsen et al.
Scheme 9: Synthesis of anthracene-embedded TCBD compound 19.
Scheme 10: Sequence of the [2 + 2] CA–RE reaction between dibenzo-fused cyclooctyne or cyclooctadiyne and TCNE...
Scheme 11: [2 + 2] CA–RE reaction between the CPP derivatives and TCNE. THF = tetrahydrofuran.
Scheme 12: [2 + 2] CA–RE reaction between ethynylfullerenes 31 and TCNE and subsequent thermal rearrangement.
Scheme 13: Pathway of the [2 + 2] CA–RE reaction between TCNE and 34, followed by additional skeletal transfor...
Scheme 14: Synthesis scheme for heterocycle 38 from the reaction between TCNE and 1 in water and a surfactant.
Scheme 15: Synthesis scheme of the CDA product 41.
Scheme 16: Synthesis of rotaxanes 44 and 46 via the [2 + 2] CA–RE reaction.
Scheme 17: Synthesis of a CuI bisphenanthroline-based rotaxane 50.
Figure 1: Structures of the chiral push–pull chromophores 51–56.
Figure 2: Structures of the axially chiral TCBD 57 and DCNQ 58 bearing a C60 core.
Figure 3: Structures of the axially chiral SubPc–TCBD–aniline conjugates 59 and 60 and the subporphyrin–TCBD–...
Figure 4: Structures of 63 and the TCBD 64.
Figure 5: Structures of the fluorophore-containing TCBDs 65–67.
Figure 6: Structures of the fluorophore-containing TCBDs 68–72.
Figure 7: Structures of the urea-containing TCBDs 73–75.
Figure 8: Structures of the fullerene–TCBD and DCNQ conjugates 76–79 and their reference compounds 80–83.
Figure 9: Structures of the ZnPc–TCBD–aniline conjugates 84 and 85.
Figure 10: Structures of the ZnP–PCBD and TCBD conjugates 86–88.
Figure 11: Structures of the porphyrin-based donor–acceptor conjugates (89–104).
Figure 12: Structures of the porphyrin–PTZ or DMA conjugates 105–112.
Figure 13: Structures of the BODIPY–Acceptor–TPA or PTZ conjugates 113–116.
Figure 14: Structures of the corrole–TCBD conjugates 117 and 118.
Figure 15: Structure of the dendritic TCBD 119.
Figure 16: Structures of the TCBDs 120–126.
Figure 17: Structures of the precursor 127 and TCBDs 128–130.
Figure 18: Structures of 131–134 utilized for BHJ OSCs.
Synthesis of imidazo[4,5-e][1,3]thiazino[2,3-c][1,2,4]triazines via a base-induced rearrangement of functionalized imidazo[4,5-e]thiazolo[2,3-c][1,2,4]triazines
- Dmitry B. Vinogradov,
- Alexei N. Izmest’ev,
- Angelina N. Kravchenko,
- Yuri A. Strelenko and
- Galina A. Gazieva
Beilstein J. Org. Chem. 2023, 19, 1047–1054, doi:10.3762/bjoc.19.80
- [2,3-c][1,2,4]triazines was synthesized via a cascade sequence of hydrolysis and skeletal rearrangement of imidazo[4,5-e]thiazolo[2,3-c][1,2,4]triazin-7(8H)-ylidene)acetic acid esters in methanol upon treatment with excess KOH. Imidazo[4,5-e]thiazolo[3,2-b][1,2,4]triazin-6(7H)-ylidene)acetic acid
- esters are also suitable substrates for the reaction. In this case hydrolysis and thiazole ring expansion were accompanied with the change of the thiazolotriazine junction type from thiazolo[3,2-b][1,2,4]triazine to thiazino[2,3-c][1,2,4]triazine. Keywords: N,S-heterocycles; ring expansion; skeletal
- rearrangement; 1,3-thiazines; thiazolidine-4-ones; Introduction Nitrogen- and sulfur-containing heterocyclic compounds are widely represented in nature and used for the synthesis of biologically active substances. Among the 1,3-thiazine derivatives, promising compounds as antimicrobial and antiviral drugs
Graphical Abstract
Figure 1: Examples of natural and synthetic bioactive 1,3-thiazine and imidazothiazolotriazine derivatives wi...
Scheme 1: Base-induced transformations and rearrangements of functionalized imidazo[4,5-e]thiazolo[3,2-b]-1,2...
Scheme 2: Alkaline hydrolysis of esters 1a,b. aDetermined by 1H NMR spectroscopy; bisolated yields.
Scheme 3: Synthesis of potassium imidazo[4,5-e][1,3]thiazino[2,3-c][1,2,4]triazine-7-carboxylates.
Scheme 4: Plausible rearrangement mechanism of imidazo[4,5-e]thiazolo[2,3-c][1,2,4]triazine 1d into imidazo[4...
Figure 2: 1H NMR spectra of the starting compound 1d (a) and the reaction mixture after 1.5 (b) and 4 (c) hou...
Scheme 5: Synthetic approaches to imidazo[4,5-e][1,3]thiazino[2,3-c][1,2,4]triazines 3a–d,j.
Scheme 6: Synthesis of imidazo[4,5-e][1,3]thiazino[2,3-c][1,2,4]triazine-7-carboxylic acids 5a–j.
Scheme 7: Synthesis of imidazo[4,5-e][1,3]thiazino[2,3-c][1,2,4]triazine-7-carboxylic acids 5k,m.
Scheme 8: Plausible path for the formation of products 9.
Figure 3: 1H NMR spectra of compounds 4a and 5a in DMSO-d6 in the region of 4.3–9.0 ppm.
Figure 4: 13C NMR GATED spectra of compounds 4a and 5a in DMSO-d6 in the region of 156.0–168.0 ppm.
Figure 5: General view of 5a in the crystal in thermal ellipsoid representation (p = 80%).
Bromination of endo-7-norbornene derivatives revisited: failure of a computational NMR method in elucidating the configuration of an organic structure
- Demet Demirci Gültekin,
- Arif Daştan,
- Yavuz Taşkesenligil,
- Cavit Kazaz,
- Yunus Zorlu and
- Metin Balci
Beilstein J. Org. Chem. 2023, 19, 764–770, doi:10.3762/bjoc.19.56
- , and assigned our product the structure (1R,2S,3R,4S,7r)-2,3,7-tribromobicyclo[2.2.1]heptane. To fit their revised structure, they proposed an alternative mechanism featuring a skeletal rearrangement without the intermediacy of a carbocation. Herein, we are not only confirming the structure originally
- bromonium ion 10, which is sterically feasable. However, after the backside attack by the bromide in 10, the resulting tribromo compound 3 undergoes an unprecedented skeletal rearrangement without a carbocation intermediate to give compound 7, their proposed alternative structure to 6. Wagner–Meerwein
- show any tendency to undergo a skeletal rearrangement, in fact with 75% it is the major product at 77 °C [4]. It is somewhat astonishing that the authors have overlooked this fact. Based on the detailed NMR arguments and experiments we presented above, supported by a sound mechanistic pathway we
Graphical Abstract
Scheme 1: Bromination of endo-7-bromonorbornene.
Figure 1: Structure 6 (our assignment) and structure 7 revised by Novitskiy and Kutateladze.
Figure 2: W or M orientaition in norbornane and the corresponding coupling constants.
Figure 3: The determined structure 6 by NMR experiments and the proposed structure 7 by computional NMR.
Figure 4: The normal and expanded 1H NMR spectra of compound 6.
Figure 5: γ-Gauche effects caused by bromine atoms in 3, 5, and 6.
Figure 6: NOE-Diff experiment. Double resonance experiment. Irradiation at the resonance frequency of protons...
Figure 7: NOE-Diff experiment. Irradiation at the resonance frequency of proton H7 (4.23 ppm).
Scheme 2: Our mechanism suggested for the formation of 6 [4].
Scheme 3: The mechanism suggested by Novitskiy and Kutateladze for the formation of 7 [3].
Figure 8: A) Molecular structure of the compound 6 with displacement ellipsoids drawn at the 30% probability ...
Transition-metal-catalyzed domino reactions of strained bicyclic alkenes
- Austin Pounder,
- Eric Neufeld,
- Peter Myler and
- William Tam
Beilstein J. Org. Chem. 2023, 19, 487–540, doi:10.3762/bjoc.19.38
Graphical Abstract
Figure 1: Ring-strain energies of homobicyclic and heterobicyclic alkenes in kcal mol−1. a) [2.2.1]-Bicyclic ...
Figure 2: a) Exo and endo face descriptions of bicyclic alkenes. b) Reactivity comparisons for different β-at...
Scheme 1: Ni-catalyzed ring-opening/cyclization cascade of heterobicyclic alkenes 1 with alkyl propiolates 2 ...
Scheme 2: Ni-catalyzed ring-opening/cyclization cascade of heterobicyclic alkenes 8 with β-iodo-(Z)-propenoat...
Scheme 3: Ni-catalyzed two- and three-component difunctionalizations of norbornene derivatives 15 with alkyne...
Scheme 4: Ni-catalyzed intermolecular three-component difunctionalization of oxabicyclic alkenes 1 with alkyn...
Scheme 5: Ni-catalyzed intermolecular three-component carboacylation of norbornene derivatives 15.
Scheme 6: Photoredox/Ni dual-catalyzed coupling of 4-alkyl-1,4-dihydropyridines 31 with heterobicyclic alkene...
Scheme 7: Photoredox/Ni dual-catalyzed coupling of α-amino radicals with heterobicyclic alkenes 30.
Scheme 8: Cu-catalyzed rearrangement/allylic alkylation of 2,3-diazabicyclo[2.2.1]heptenes 47 with Grignard r...
Scheme 9: Cu-catalyzed aminoboration of bicyclic alkenes 1 with bis(pinacolato)diboron (B2pin2) (53) and O-be...
Scheme 10: Cu-catalyzed borylalkynylation of oxabenzonorbornadiene (30b) with B2pin2 (53) and bromoalkynes 62.
Scheme 11: Cu-catalyzed borylacylation of bicyclic alkenes 1.
Scheme 12: Cu-catalyzed diastereoselective 1,2-difunctionalization of oxabenzonorbornadienes 30 for the synthe...
Scheme 13: Fe-catalyzed carbozincation of heterobicyclic alkenes 1 with arylzinc reagents 74.
Scheme 14: Co-catalyzed addition of arylzinc reagents of norbornene derivatives 15.
Scheme 15: Co-catalyzed ring-opening/dehydration of oxabicyclic alkenes 30 via C–H activation of arenes.
Scheme 16: Co-catalyzed [3 + 2] annulation/ring-opening/dehydration domino reaction of oxabicyclic alkenes 1 w...
Scheme 17: Co-catalyzed enantioselective carboamination of bicyclic alkenes 1 via C–H functionalization.
Scheme 18: Ru-catalyzed cyclization of oxabenzonorbornene derivatives with propargylic alcohols for the synthe...
Scheme 19: Ru-catalyzed coupling of oxabenzonorbornene derivatives 30 with propargylic alcohols and ethers 106...
Scheme 20: Ru-catalyzed ring-opening/dehydration of oxabicyclic alkenes via the C–H activation of anilides.
Scheme 21: Ru-catalyzed of azabenzonorbornadiene derivatives with arylamides.
Scheme 22: Rh-catalyzed cyclization of bicyclic alkenes with arylboronate esters 118.
Scheme 23: Rh-catalyzed cyclization of bicyclic alkenes with dienyl- and heteroaromatic boronate esters.
Scheme 24: Rh-catalyzed domino lactonization of doubly bridgehead-substituted oxabicyclic alkenes with seconda...
Scheme 25: Rh-catalyzed domino carboannulation of diazabicyclic alkenes with 2-cyanophenylboronic acid and 2-f...
Scheme 26: Rh-catalyzed synthesis of oxazolidinone scaffolds 147 through a domino ARO/cyclization of oxabicycl...
Scheme 27: Rh-catalyzed oxidative coupling of salicylaldehyde derivatives 151 with diazabicyclic alkenes 130a.
Scheme 28: Rh-catalyzed reaction of O-acetyl ketoximes with bicyclic alkenes for the synthesis of isoquinoline...
Scheme 29: Rh-catalyzed domino coupling reaction of 2-phenylpyridines 165 with oxa- and azabicyclic alkenes 30....
Scheme 30: Rh-catalyzed domino dehydrative naphthylation of oxabenzonorbornadienes 30 with N-sulfonyl 2-aminob...
Scheme 31: Rh-catalyzed domino dehydrative naphthylation of oxabenzonorbornadienes 30 with arylphosphine deriv...
Scheme 32: Rh-catalyzed domino ring-opening coupling reaction of azaspirotricyclic alkenes using arylboronic a...
Scheme 33: Tandem Rh(III)/Sc(III)-catalyzed domino reaction of oxabenzonorbornadienes 30 with alkynols 184 dir...
Scheme 34: Rh-catalyzed asymmetric domino cyclization and addition reaction of 1,6-enynes 194 and oxa/azabenzo...
Scheme 35: Rh/Zn-catalyzed domino ARO/cyclization of oxabenzonorbornadienes 30 with phosphorus ylides 201.
Scheme 36: Rh-catalyzed domino ring opening/lactonization of oxabenzonorbornadienes 30 with 2-nitrobenzenesulf...
Scheme 37: Rh-catalyzed domino C–C/C–N bond formation of azabenzonorbornadienes 30 with aryl-2H-indazoles 210.
Scheme 38: Rh/Pd-catalyzed domino synthesis of indole derivatives with 2-(phenylethynyl)anilines 212 and oxabe...
Scheme 39: Rh-catalyzed domino carborhodation of heterobicyclic alkenes 30 with B2pin2 (53).
Scheme 40: Rh-catalyzed three-component 1,2-carboamidation reaction of bicyclic alkenes 30 with aromatic and h...
Scheme 41: Pd-catalyzed diarylation and dialkenylation reactions of norbornene derivatives.
Scheme 42: Three-component Pd-catalyzed arylalkynylation reactions of bicyclic alkenes.
Scheme 43: Three-component Pd-catalyzed arylalkynylation reactions of norbornene and DFT mechanistic study.
Scheme 44: Pd-catalyzed three-component coupling N-tosylhydrazones 236, aryl halides 66, and norbornene (15a).
Scheme 45: Pd-catalyzed arylboration and allylboration of bicyclic alkenes.
Scheme 46: Pd-catalyzed, three-component annulation of aryl iodides 66, alkenyl bromides 241, and bicyclic alk...
Scheme 47: Pd-catalyzed double insertion/annulation reaction for synthesizing tetrasubstituted olefins.
Scheme 48: Pd-catalyzed aminocyclopropanation of bicyclic alkenes 1 with 5-iodopent-4-enylamine derivatives 249...
Scheme 49: Pd-catalyzed, three-component coupling of alkynyl bromides 62 and norbornene derivatives 15 with el...
Scheme 50: Pd-catalyzed intramolecular cyclization/ring-opening reaction of heterobicyclic alkenes 30 with 2-i...
Scheme 51: Pd-catalyzed dimer- and trimerization of oxabenzonorbornadiene derivatives 30 with anhydrides 268.
Scheme 52: Pd-catalyzed Catellani-type annulation and retro-Diels–Alder of norbornadiene 15b yielding fused xa...
Scheme 53: Pd-catalyzed hydroarylation and heteroannulation of urea-derived bicyclic alkenes 158 and aryl iodi...
Scheme 54: Access to fused 8-membered sulfoximine heterocycles 284/285 via Pd-catalyzed Catellani annulation c...
Scheme 55: Pd-catalyzed 2,2-bifunctionalization of bicyclic alkenes 1 generating spirobicyclic xanthone deriva...
Scheme 56: Pd-catalyzed Catellani-type annulation and retro-Diels–Alder of norbornadiene (15b) producing subst...
Scheme 57: Pd-catalyzed [2 + 2 + 1] annulation furnishing bicyclic-fused indanes 281 and 283.
Scheme 58: Pd-catalyzed ring-opening/ring-closing cascade of diazabicyclic alkenes 130a.
Scheme 59: Pd-NHC-catalyzed cyclopentannulation of diazabicyclic alkenes 130a.
Scheme 60: Pd-catalyzed annulation cascade generating diazabicyclic-fused indanones 292 and indanols 294.
Scheme 61: Pd-catalyzed skeletal rearrangement of spirotricyclic alkenes 176 towards large polycyclic benzofur...
Scheme 62: Pd-catalyzed oxidative annulation of aromatic enamides 298 and diazabicyclic alkenes 130a.
Scheme 63: Accessing 3,4,5-trisubstituted cyclopentenes 300, 301, 302 via the Pd-catalyzed domino reaction of ...
Scheme 64: Palladacycle-catalyzed ring-expansion/cyclization domino reactions of terminal alkynes and bicyclic...
Scheme 65: Pd-catalyzed carboesterification of norbornene (15a) with alkynes, furnishing α-methylene γ-lactone...
Synthesis of functionalized imidazo[4,5-e]thiazolo[3,2-b]triazines by condensation of imidazo[4,5-e]triazinethiones with DMAD or DEAD and rearrangement to imidazo[4,5-e]thiazolo[2,3-c]triazines
- Alexei N. Izmest’ev,
- Dmitry B. Vinogradov,
- Natalya G. Kolotyrkina,
- Angelina N. Kravchenko and
- Galina A. Gazieva
Beilstein J. Org. Chem. 2021, 17, 1141–1148, doi:10.3762/bjoc.17.87
- based on the sequential condensation of imidazo[4,5-e]-1,2,4-triazine-3-thiones 3 with DMAD or DEAD and skeletal rearrangement of linear imidazo[4,5-e]thiazolo[3,2-b]-1,2,4-triazines 4 into isomeric imidazo[4,5-e]thiazolo[2,3-с]-1,2,4-triazines 5 having an angular structure. Results and Discussion We
- of imidazo[4,5-e]thiazolo[3,2-b]triazines with carbonyl compounds, namely, aromatic aldehydes and isatins, are capable of skeletal rearrangement of the thiazolotriazine system proceeding in methanol upon treatment with KOH and resulting in the corresponding isomeric imidazo[4,5-e]thiazolo[2,3-c
- 40% KOH aqueous solution resulted in a skeletal rearrangement of the tricyclic system, which, however, was accompanied by reesterification with methanol and partial hydrolysis of the ester group. As a result, the methyl ester 5a was obtained in 66% yield (Scheme 3). Rearrangement of 1,3-dimethyl- and
Graphical Abstract
Figure 1: Biologically active compounds having thiazolidin-4-one and thiazolo-1,2,4-triazine units.
Scheme 1: Regioselectivity of the cyclization of 3-thioxo-1,2,4-triazin-5-ones 1 with DMAD (A) and general co...
Scheme 2: Synthesis of imidazo[4,5-e]thiazolo[3,2-b]triazine derivatives 4a–n by the reaction of imidazo[4,5-...
Scheme 3: Reaction of imidazo[4,5-e]thiazolo[3,2-b]triazine 4h with aqueous KOH.
Scheme 4: Rearrangement of imidazo[4,5-e]thiazolo[3,2-b]triazines 4a–n into imidazo[4,5-e]thiazolo[2,3-c]tria...
Scheme 5: One-pot synthesis of compounds 5a,b,h,i from imidazo[4,5-e]triazines 3a,b.
Scheme 6: Plausible mechanism of the formation and the rearrangement of compounds 4 into isomers 5.
Figure 2: 1H NMR spectra of compounds 4h and 5h in DMSO-d6 in the region of 3.5–8.8 ppm.
Figure 3: X-ray crystal structure of compound 5i.
CF3-substituted carbocations: underexploited intermediates with great potential in modern synthetic chemistry
- Anthony J. Fernandes,
- Armen Panossian,
- Bastien Michelet,
- Agnès Martin-Mingot,
- Frédéric R. Leroux and
- Sébastien Thibaudeau
Beilstein J. Org. Chem. 2021, 17, 343–378, doi:10.3762/bjoc.17.32
Graphical Abstract
Figure 1: Stabilizing interaction in the CF3CH2+ carbenium ion (top) and structure of the first observable fl...
Scheme 1: Isodesmic equations accounting for the destabilizing effect of the CF3 group. ΔE in kcal⋅mol−1, cal...
Scheme 2: Stabilizing effect of fluorine atoms by resonance electron donation in carbenium ions (δ in ppm).
Scheme 3: Direct in situ NMR observation of α-(trifluoromethyl)carbenium ion or protonated alcohols. Δδ = δ19...
Scheme 4: Reported 13C NMR chemical shifts for the α-(trifluoromethyl)carbenium ion 10c (δ in ppm).
Scheme 5: Direct NMR observation of α-(trifluoromethyl)carbenium ions in situ (δ in ppm).
Scheme 6: Illustration of the ion pair solvolysis mechanism for sulfonate 13f. YOH = solvent.
Figure 2: Solvolysis rate for 13a–i and 17.
Figure 3: Structures of allyl triflates 18 and 19 and allyl brosylate 20. Bs = p-BrC6H4SO2.
Figure 4: Structure of tosylate derivatives 21.
Figure 5: a) Structure of triflate derivatives 22. b) Stereochemistry outcomes of the reaction starting from (...
Scheme 7: Solvolysis reaction of naphthalene and anthracenyl derivatives 26 and 29.
Figure 6: Structure of bisarylated derivatives 34.
Figure 7: Structure of bisarylated derivatives 36.
Scheme 8: Reactivity of 9c in the presence of a Brønsted acid.
Scheme 9: Cationic electrocyclization of 38a–c under strongly acidic conditions.
Scheme 10: Brønsted acid-catalyzed synthesis of indenes 42 and indanes 43.
Scheme 11: Reactivity of sulfurane 44 in triflic acid.
Scheme 12: Solvolysis of triflate 45f in alcoholic solvents.
Scheme 13: Synthesis of labeled 18O-52.
Scheme 14: Reactivity of sulfurane 53 in triflic acid.
Figure 8: Structure of tosylates 56 and 21f.
Scheme 15: Resonance forms in benzylic carbenium ions.
Figure 9: Structure of pyrrole derivatives 58 and 59.
Scheme 16: Resonance structure 60↔60’.
Scheme 17: Ga(OTf)3-catalyzed synthesis of 3,3’- and 3,6’-bis(indolyl)methane from trifluoromethylated 3-indol...
Scheme 18: Proposed reaction mechanism.
Scheme 19: Metal-free 1,2-phosphorylation of 3-indolylmethanols.
Scheme 20: Superacid-mediated arylation of thiophene derivatives.
Scheme 21: In situ mechanistic NMR investigations.
Scheme 22: Proposed mechanisms for the prenyltransferase-catalyzed condensation.
Scheme 23: Influence of a CF3 group on the allylic SN1- and SN2-mechanism-based reactions.
Scheme 24: Influence of the CF3 group on the condensation reaction.
Scheme 25: Solvolysis of 90 in TFE.
Scheme 26: Solvolysis of allyl triflates 94 and 97 and isomerization attempt of 96.
Scheme 27: Proposed mechanism for the formation of 95.
Scheme 28: Formation of α-(trifluoromethyl)allylcarbenium ion 100 in a superacid.
Scheme 29: Lewis acid activation of CF3-substituted allylic alcohols.
Scheme 30: Bimetallic-cluster-stabilized α-(trifluoromethyl)carbenium ions.
Scheme 31: Reactivity of cluster-stabilized α-(trifluoromethyl)carbenium ions.
Scheme 32: α-(Trifluoromethyl)propargylium ion 122↔122’ generated from silyl ether 120 in a superacid.
Scheme 33: Formation of α-(trifluoromethyl)propargylium ions from CF3-substituted propargyl alcohols.
Scheme 34: Direct NMR observation of the protonation of some trifluoromethyl ketones in situ and the correspon...
Scheme 35: Selected resonance forms in protonated fluoroketone derivatives.
Scheme 36: Acid-catalyzed Friedel–Crafts reactions of trifluoromethyl ketones 143a,b and 147a–c.
Scheme 37: Enantioselective hydroarylation of CF3-substituted ketones.
Scheme 38: Acid-catalyzed arylation of ketones 152a–c.
Scheme 39: Reactivity of 156 in a superacid.
Scheme 40: Reactivity of α-CF3-substituted heteroaromatic ketones and alcohols as well as 1,3-diketones.
Scheme 41: Reactivity of 168 with benzene in the presence of a Lewis or Brønsted acid.
Scheme 42: Acid-catalyzed three-component asymmetric reaction.
Scheme 43: Anodic oxidation of amines 178a–c and proposed mechanism.
Scheme 44: Reactivity of 179b in the presence of a strong Lewis acid.
Scheme 45: Trifluoromethylated derivatives as precursors of trifluoromethylated iminium ions.
Scheme 46: Mannich reaction with trifluoromethylated hemiaminal 189.
Scheme 47: Suitable nucleophiles reacting with 192 after Lewis acid activation.
Scheme 48: Strecker reaction involving the trifluoromethylated iminium ion 187.
Scheme 49: Reactivity of 199 toward nucleophiles.
Scheme 50: Reactivity of 204a with benzene in the presence of a Lewis acid.
Scheme 51: Reactivity of α-(trifluoromethyl)-α-chloro sulfides in the presence of strong Lewis acids.
Scheme 52: Anodic oxidation of sulfides 213a–h and Pummerer rearrangement.
Scheme 53: Mechanism for the electrochemical oxidation of the sulfide 213a.
Scheme 54: Reactivity of (trifluoromethyl)diazomethane (217a) in HSO3F.
Figure 10: a) Structure of diazoalkanes 217a–c and b) rate-limiting steps of their decomposition.
Scheme 55: Deamination reaction of racemic 221 and enantioenriched (S)-221.
Scheme 56: Deamination reaction of labeled 221-d2. Elimination products were formed in this reaction, the yiel...
Scheme 57: Deamination reaction of 225-d2. Elimination products were also formed in this reaction in undetermi...
Scheme 58: Formation of 229 from 228 via 1,2-H-shift.
Scheme 59: Deamination reaction of 230. Elimination products were formed in this reaction, the yield of which ...
Scheme 60: Deamination of several diazonium ions. Elimination products were formed in these reactions, the yie...
Scheme 61: Solvolysis reaction mechanism of alkyl tosylates.
Scheme 62: Solvolysis outcome for the tosylates 248 and 249 in HSO3FSbF5.
Figure 11: Solvolysis rate of 248, 249, 252, and 253 in 91% H2SO4.
Scheme 63: Illustration of the reaction pathways. TsCl, pyridine, −5 °C (A); 98% H2SO4, 30 °C (B); 98% H2SO4, ...
Scheme 64: Proposed solvolysis mechanism for the aliphatic tosylate 248.
Scheme 65: Solvolysis of the derivatives 259 and 260.
Scheme 66: Solvolysis of triflate 261. SOH = solvent.
Scheme 67: Intramolecular Friedel–Crafts alkylations upon the solvolysis of triflates 264 and 267.
Scheme 68: α-CF3-enhanced γ-silyl elimination of cyclobutyltosylates 270a,b.
Scheme 69: γ-Silyl elimination in the synthesis of a large variety of CF3-substituted cyclopropanes. Pf = pent...
Scheme 70: Synthetic pathways to 281. aNMR yields.
Scheme 71: The cyclopropyl-substituted homoallylcyclobutylcarbenium ion manifold.
Scheme 72: Reactivity of CF3-substituted cyclopropylcarbinyl derivatives 287a–c. LG = leaving group.
Scheme 73: Reactivity of CF3-substituted cyclopropylcarbinyl derivatives 291a–c.
Scheme 74: Superacid-promoted dimerization or TFP.
Scheme 75: Reactivity of TFP in a superacid.
Scheme 76: gem-Difluorination of α-fluoroalkyl styrenes via the formation of a “hidden” α-RF-substituted carbe...
Scheme 77: Solvolysis of CF3-substituted pentyne 307.
Scheme 78: Photochemical rearrangement of 313.
Figure 12: Structure of 2-norbornylcarbenium ion 318 and argued model for the stabilization of this cation.
Figure 13: Structures and solvolysis rate (TFE, 25 °C) of the sulfonates 319–321. Mos = p-MeOC6H4SO2.
Scheme 79: Mechanism for the solvolysis of 323. SOH = solvent.
Scheme 80: Products formed by the hydrolysis of 328.
Scheme 81: Proposed carbenium ion intermediates in an equilibrium during the solvolysis of tosylates 328, 333,...
On the mass spectrometric fragmentations of the bacterial sesterterpenes sestermobaraenes A–C
- Anwei Hou and
- Jeroen S. Dickschat
Beilstein J. Org. Chem. 2020, 16, 2807–2819, doi:10.3762/bjoc.16.231
- first instance, it seems difficult to parallel this for 2, but if for the first steps after ionisation to 2•+ a skeletal rearrangement to t2•+ and a hydrogen transfer to u2•+ are assumed, the parallelism of the fragmentation mechanisms becomes more obvious (Scheme 4C). Subsequent steps may include an
- a multistep process (Scheme 6A). Starting from 3•+, a hydride shift to n3•+ and skeletal rearrangement lead to o3•+. A subsequent hydrogen rearrangement of this primary radical yields the tertiary radical p3•+ that can undergo an α-fragmentation to q3•+, followed by hydrogen rearrangement to r3
Graphical Abstract
Figure 1: The structures of the bacterial sesterterpenes sestermobaraenes A–F (1–6) and sestermobaraol (7) fr...
Figure 2: Position-specific mass shift analyses for 1. Carbons that contribute fully to the formation of a fr...
Scheme 1: The EIMS fragmentation mechanisms for 1 explaining the formation of the fragment ions at m/z = 325,...
Scheme 2: The EIMS fragmentation mechanisms for 1 explaining the formation of fragment ions at m/z = 206 and ...
Figure 3: Position-specific mass shift analyses for 2. The carbons that contribute fully to the formation of ...
Scheme 3: The EIMS fragmentation mechanisms for 2 explaining the formation of the fragment ions at m/z = 325,...
Scheme 4: The EIMS fragmentation mechanisms for 2 explaining the formation of the fragment ions at m/z = 203 ...
Figure 4: The position-specific mass shift analyses for 3. Carbons that contribute fully to the formation of ...
Scheme 5: The EIMS fragmentation mechanisms for 3 explaining the formation of the fragment ions at m/z = 325,...
Scheme 6: The EIMS fragmentation mechanisms for 3 explaining the formation of the fragment ion at m/z = 206 a...
Accelerating fragment-based library generation by coupling high-performance photoreactors with benchtop analysis
- Quentin Lefebvre,
- Christophe Salomé and
- Thomas C. Fessard
Beilstein J. Org. Chem. 2020, 16, 982–988, doi:10.3762/bjoc.16.87
- preliminary quality control (QC) could be performed using a benchtop 60 MHz NMR machine (Figure 3). Structural information was obtained to corroborate mass spectrometry data, an important information when dealing with strained bicycles or spirocycles, which could be prone to skeletal rearrangement. If
Graphical Abstract
Scheme 1: One-day workflow for fragment-based library generation. QC: Quality control. MPLC: Medium-pressure ...
Figure 1: Top: high-power blue LED photoreactors. Bottom, from left to right: photoreactor OFF, ON, and ON th...
Figure 2: TLC–MS equipment: analysis of 5 reactions in 5 minutes.
Figure 3: Pre-QC validation by 60 MHz benchtop NMR.
Scheme 2: Scope of the fragment-based library generation: BCP-amines and azetidines. See Supporting Information File 1 for experimental de...
Scheme 3: Scope of the fragment-based library generation: pyrrolidines, piperidines and morpholines. See Supporting Information File 1 for...
An improved preparation of phorbol from croton oil
- Alberto Pagani,
- Simone Gaeta,
- Andrei I. Savchenko,
- Craig M. Williams and
- Giovanni Appendino
Beilstein J. Org. Chem. 2017, 13, 1361–1367, doi:10.3762/bjoc.13.133
- degradative studies had proved unable to address because of the tendency of phorbol to skeletal rearrangement and to its idiosyncratic chemical reactivity [6]. By this time, the medicinal use of croton oil had become obsolete, but interest had been rekindled by the discovery of its co-carcinogenic properties
Graphical Abstract
Figure 1: The major diterpene polyols from croton oil [phorbol (1a), 4α-phorbol (2), 4-deoxy-4α-phorbol (3a)]...
Evidencing an inner-sphere mechanism for NHC-Au(I)-catalyzed carbene-transfer reactions from ethyl diazoacetate
- Manuel R. Fructos,
- Juan Urbano,
- M. Mar Díaz-Requejo and
- Pedro J. Pérez
Beilstein J. Org. Chem. 2015, 11, 2254–2260, doi:10.3762/bjoc.11.245
- skeletal rearrangement of the [2 + 2] cycloaddition of 1,6-enynes [4] is shown in Scheme 1, where three different gold–carbene intermediates are involved in the possible transformations. A different reaction in which the formation of gold–carbene intermediates has been proposed arises from the interaction
- relative substrate:catalyst ratio, at a constant catalyst value. Bottom: Plots of kobs vs substrate concentration showing a direct correlation between both magnitudes. The experimental device for the measurement of N2 evolution. The Au(I)-catalyzed skeletal rearrangement of the [2 + 2] cycloaddition of 1,6
Graphical Abstract
Scheme 1: The Au(I)-catalyzed skeletal rearrangement of the [2 + 2] cycloaddition of 1,6-enynes that involves...
Scheme 2: The catalytic activity of IPrAuCl + NaBArF4 in the carbene-transfer reaction to styrene or methanol....
Scheme 3: The gold-promoted decarbenation reaction described by Echavarren and co-workers.
Scheme 4: (a) General representation of the metal-catalyzed carbene-transfer reaction (olefin cyclopropanatio...
Figure 1: Plot of evolved nitrogen with time for the reactions of EDA with styrene or methanol.
Figure 2: Top: Plots of evolved nitrogen with time for the reactions of EDA with styrene (left) or methanol (...
Scheme 5: The outer- and inner-sphere routes for this transformation.
Figure 3: The experimental device for the measurement of N2 evolution.
A facile synthesis of functionalized 7,8-diaza[5]helicenes through an oxidative ring-closure of 1,1’-binaphthalene-2,2’-diamines (BINAMs)
- Youhei Takeda,
- Masato Okazaki,
- Yoshiaki Maruoka and
- Satoshi Minakata
Beilstein J. Org. Chem. 2015, 11, 9–15, doi:10.3762/bjoc.11.2
- forming reaction resulted in much lower yield of 2a (Table 1, entry 2) while the skeletal rearrangement product was obtained as a main product (51% yield) [31], showing the obvious superiority of t-BuOCl as an oxidant. Encouraged by these results, a variety of chlorine-containing oxidants were tested to
Graphical Abstract
Scheme 1: Synthetic routes to 7,8-diaza[5]helicene.
Scheme 2: Oxidant-controlled transformations of BINAMs.
Scheme 3: Substrate scope of the oxidative ring-closure of BINAMs. Reaction conditions: 1 (0.1 mmol), t-BuOCl...
Scheme 4: Oxidative ring-closure of 3.
Scheme 5: A possible reaction pathway of the oxidative ring-closure of 1a.
Figure 1: UV–vis absorption spectra of 2a, 2b, 2d, and 2f.
Isotopic labelling studies for a gold-catalysed skeletal rearrangement of alkynyl aziridines
- Paul W. Davies,
- Nicolas Martin and
- Neil Spencer
Beilstein J. Org. Chem. 2011, 7, 839–846, doi:10.3762/bjoc.7.96
- aziridines into 2,4-disubstituted pyrroles. Two isotopomers of the expected skeletal rearrangement product were identified using 13C-labelling and led to a revised mechanism featuring two distinct skeletal rearrangements. The mechanistic proposal has been rationalised against the reaction of a range of 13C
- - and deuterium-labelled substrates. Keywords: 1,2-aryl shift; cycloisomerisation; gold; isotopic labelling; pyrrole; skeletal rearrangement; Introduction Gold-catalysed cycloisomerisation reactions have emerged as powerful methods to construct a diverse array of hetero- and carbocyclic motifs under
- other reports into π-acid promoted alkynyl aziridine cycloisomerisations without skeletal rearrangement [20][21][22][23]. Our working mechanism to explain this reaction divergence centred on the electrophilic activation of the alkyne in A triggering a ring-expansion to a common intermediate B from which
Graphical Abstract
Scheme 1: Gold-catalysed cycloisomerisations of aryl–alkynyl aziridine to pyrroles.
Scheme 2: Working mechanism to rationalise the formation of two regiosomeric pyrroles in the gold catalysed c...
Scheme 3: Bond fissions featured in the proposed mechanistic hypothesis and the initial mechanism probe.
Scheme 4: Preparation of D-labelled alkynyl aziridine 4. DMP = Dess–Martin periodinane.
Scheme 5: Reaction of deuterated alkynyl aziridine 4 in the skeletal rearrangement reaction.
Scheme 6: Preparation of 13C-enriched alkynyl aziridines.
Scheme 7: Cycloisomerisation of 11 in the skeletal rearrangement reaction.
Scheme 8: Cycloisomerisation of 11 to give 2,5-disubstituted pyrrole.
Scheme 9: Cycloisomerisation of 14 in the skeletal rearrangement reaction.
Scheme 10: Cycloisomerisation of 15 in the skeletal rearrangement reaction.
Scheme 11: Revised mechanism for the formation of 2,4-isomers by skeletal rearrangement.
Scheme 12: Synthesis of alkynyl aziridines 30 and 31.
Scheme 13: Electronic effects on the outcome of the skeletal rearrangement processes.
Scheme 14: Mechanistic rationale for the deuterium labelling study using Ph3PAuCl/AgOTf.
When cyclopropenes meet gold catalysts
- Frédéric Miege,
- Christophe Meyer and
- Janine Cossy
Beilstein J. Org. Chem. 2011, 7, 717–734, doi:10.3762/bjoc.7.82
- , the cyclopropene carbon atoms become directly linked to those of the alkyne with no skeletal rearrangement (Scheme 29) [26]. However, the substituents were found to exert an important influence on the outcome of the reaction. Indeed, the secondary propargylic alcohols 82a and 82b, in which the alkyne
Graphical Abstract
Scheme 1: General reactivity of cyclopropenes in the presence of gold catalysts.
Scheme 2: Cationic organogold species generated from cyclopropenone acetals.
Scheme 3: Rotation barriers around the C2–C3 bond (M06 DFT calculations).
Scheme 4: Au–C1 bond length in organogold species of type D.
Scheme 5: Gold-catalyzed addition of alcohols or water to cyclopropene 8.
Scheme 6: Gold-catalyzed addition of alcohols to cyclopropene 10.
Scheme 7: Mechanism of the gold-catalyzed addition of alcohols to cyclopropenes.
Scheme 8: Synthesis of tert-allylic ethers from cyclopropenes and allenes.
Scheme 9: Oxidation of the intermediate gold–carbene with diphenylsulfoxide.
Scheme 10: Gold, copper and Lewis acid-catalyzed reactions of cyclopropene 18.
Scheme 11: Mechanism of the Lewis acid-catalyzed reactions of cyclopropene 18.
Scheme 12: Gold-catalyzed rearrangement of vinylcyclopropenes 25.
Scheme 13: Gold-catalyzed rearrangement of cyclopropenes 27 to indenes 28.
Scheme 14: Gold-catalyzed rearrangement of cyclopropenes 29 to indenes 30.
Scheme 15: Gold-catalyzed rearrangement of cyclopropenyl ester 34a.
Scheme 16: Gold-catalyzed reactions of cyclopropenyl esters 34b–34d.
Scheme 17: Gold-catalyzed reactions of cyclopropenylsilane 34e.
Scheme 18: Gold-catalyzed rearrangement of cyclopropenylmethyl acetates.
Scheme 19: Mechanism of the gold-catalyzed rearrangement of cyclopropenes 39.
Scheme 20: Gold-catalyzed cyclopropanation of styrene with cyclopropene 8.
Scheme 21: Representative reactions of carbene precursors on gold metal.
Scheme 22: Intermolecular olefin cyclopropanation with gold carbenes generated from cyclopropenes.
Scheme 23: Gold-catalyzed formation of trienes from cyclopropenes and furans.
Scheme 24: Gold-catalyzed formation of trienes from cyclopropenes and furans.
Scheme 25: Gold-catalyzed formation of trienes from cyclopropenes and furans.
Scheme 26: Gold-catalyzed cycloisomerization of cyclopropene-ene 59.
Scheme 27: Gold-catalyzed cycloisomerization of substituted allyl cyclopropenyl carbinyl ethers 62a–62f.
Scheme 28: Gold-catalyzed cycloisomerization of cyclopropene-enes.
Scheme 29: Gold-catalyzed cycloisomerization of cyclopropene-ynes.
Scheme 30: Formation of products arising from a double cleavage process in the gold-catalyzed cycloisomerizati...
Scheme 31: Gold-catalyzed cycloisomerization of cyclopropene-ynes involving a double cleavage process.
Scheme 32: Gold-catalyzed reaction of cyclopropene-ynes, cyclopropene-enes and cyclopropene-allenes.
