Formation of an exceptionally stable ketene during phototransformations of bicyclo[2.2.2]oct-5-en-2-ones having mixed chromophores

• Asitanga Ghosh

Beilstein J. Org. Chem. 2020, 16, 2297–2303, doi:10.3762/bjoc.16.190

• distribution of these photoproducts may be wavelength dependent [7]. In order to investigate the photoreaction of such enones, we observed a complete 1,2-acyl shift (1,2-AS) photoproduct formation when 1a–h have been irradiated (Scheme 1) [14][16]. We also observed that such a rearrangement took place very

• , the photorearrangement route is selectively from the α,β-enone part and we confirmed that the irradiation follows a type B rearrangement (Scheme 2) [16]. Another interesting set of competitive 1,5-(C–O) acyl shift rearrangements (formation of vinyl ketene) with that of 1,2-AS were observed when

Synthetic approaches to bowl-shaped π-conjugated sumanene and its congeners

• Shakeel Alvi and
• Rashid Ali

Beilstein J. Org. Chem. 2020, 16, 2212–2259, doi:10.3762/bjoc.16.186

Reactions of 3-aryl-1-(trifluoromethyl)prop-2-yn-1-iminium salts with 1,3-dienes and styrenes

• Thomas Schneider,
• Michael Keim,
• Bianca Seitz and
• Gerhard Maas

Beilstein J. Org. Chem. 2020, 16, 2064–2072, doi:10.3762/bjoc.16.173

• analogous to 21 could be isolated [56]. A cationic 1,5-cylization converts 21 into cyclopentene 22, from which fulvene 19 is formed by deprotonation and a formal 1,4-shift of the NMe2 group. The details of this rearrangement are not known, an N,N-dimethyldihydropyrrolium intermediate may be involved

Syntheses of spliceostatins and thailanstatins: a review

• William A. Donaldson

Beilstein J. Org. Chem. 2020, 16, 1991–2006, doi:10.3762/bjoc.16.166

• ] was followed by a 3-O-vinylation. A thermal 3,3-sigmatropic Claisen rearrangement of 62 gave the cis-2,6-disubstituted dihydropyran 63, which upon sequential Wittig olefination with 2-(triphenylphosporanylidene)propanal and then methylenetriphenylphosphorane yielded the diene 64. The removal of the di

• with a 6:1 diastereoselectivity. The Red-Al reduction of 94, protection of the 2° alcohol, and reduction of the enoate to an allylic alcohol were prerequisites for the stereoselective 2,3-sigmatropic selenoxide rearrangement to generate 95. Further protecting group manipulation and Johnson–Lemieux

Selective preparation of tetrasubstituted fluoroalkenes by fluorine-directed oxetane ring-opening reactions

• Clément Q. Fontenelle,
• Thibault Thierry,
• Romain Laporte,
• Emmanuel Pfund and
• Thierry Lequeux

Beilstein J. Org. Chem. 2020, 16, 1936–1946, doi:10.3762/bjoc.16.160

• olefination or defluorination reactions or a sigmatropic rearrangement, but these approaches are limited and do not allow the synthesis of tetrasubstituted fluoroalkenes with good control of their geometry [18][19][20][21]. In order to develop a selective synthesis for tetrasubstituted fluoroalkenes we

• Smiles rearrangement occurred leading to fluoroethylene and benzothiazolone. Therefore, its benzylation was explored under acidic conditions with benzyl trichloroacetimidate (1.5 equiv) and a catalytic amount of trifluoromethanesulfonic acid. This gave benzyl ether 7 as a 2.5:1 mixture with N

• already reported in the literature from oxetane-containing α,β-unsaturated carbonyl derivatives through a Lewis acid-catalyzed rearrangement [31]. When the previous conditions (HBr/AcOH) were tried (3.5 h, 0 °C to 20 °C), hydroxymethyllactone 14 (87%, Table 4, entry 1) was the main product with traces of

Synthesis and highly efficient light-induced rearrangements of diphenylmethylene(2-benzo[b]thienyl)fulgides and fulgimides

• Vladimir P. Rybalkin,
• Sofiya Yu. Zmeeva,
• Lidiya L. Popova,
• Valerii V. Tkachev,
• Andrey N. Utenyshev,
• Olga Yu. Karlutova,
• Alexander D. Dubonosov,
• Vladimir A. Bren,
• Sergey M. Aldoshin and
• Vladimir I. Minkin

Beilstein J. Org. Chem. 2020, 16, 1820–1829, doi:10.3762/bjoc.16.149

• undergo an irreversible transformation leading to decoloration of their solutions. This rearrangement with the formation of the dihydronaphthalene core appeared to be by 2–3 orders of magnitude more efficient than for the known diphenylmethylene(aryl(hetaryl))fulgides. The molecular structures of E- and Z

• -isomers and of products of the photoinduced rearrangement completed by 1,5-H shift reaction, 3a,4-dihydronaphtho[2,3-c]furans(pyrroles) C, were established based on the data of 1H and 13C NMR spectroscopy and X-ray diffraction studies. Keywords: benzo[b]thiophene; fulgide; fulgimide; photorearrangement

• photochromic properties of 2-benzo[b]thienylfulgides [22]. UV irradiation of acetonitrile solutions of these compounds results in the electrocyclic hexatriene–cyclohexadiene rearrangement of the ring-opened isomers O into the colored ring-closed ones C (Scheme 1) which exhibit enhanced spectral characteristics

Microwave-assisted efficient one-pot synthesis of N²-(tetrazol-5-yl)-6-aryl/heteroaryl-5,6-dihydro-1,3,5-triazine-2,4-diamines

• Moustafa Sherief Moustafa,
• Ramadan Ahmed Mekheimer,
• Saleh Mohammed Al-Mousawi,
• Mohamed Abd-Elmonem,
• Hesham El-Zorba,
• Afaf Mohamed Abdel Hameed,
• Tahany Mahmoud Mohamed and
• Kamal Usef Sadek

Beilstein J. Org. Chem. 2020, 16, 1706–1712, doi:10.3762/bjoc.16.142

• the synthesis of 6-substituted-N2-aryl-1,6-dihydro-1,3,5-triazine-2,4-diamines via the reaction of aromatic amines, cyanoguanidine, and ketones which afforded the corresponding 1-aryl-1,6-dihydro-6-substituted-1,3,5-triazine-2,4-diamines in 21–56% yields followed by Dimroth rearrangement utilizing

• cyanoguanidine 5 to the formed Schiff’s base (route c). Product 4 was the sole isolable product as under reflux in pyridine as base, compound 8 well undergoes a Dimroth rearrangement forming the more thermodynamically stable product 4 [33]. We established route c, as the formation of the Schiff base is more

Rearrangement of o-(pivaloylaminomethyl)benzaldehydes: an experimental and computational study

• Csilla Hargitai,
• Györgyi Koványi-Lax,
• Tamás Nagy,
• Péter Ábrányi-Balogh,
• András Dancsó,
• Gábor Tóth,
• Judit Halász,
• Angéla Pandur,
• Gyula Simig and
• Balázs Volk

Beilstein J. Org. Chem. 2020, 16, 1636–1648, doi:10.3762/bjoc.16.136

• , and to explain the observed product distributions and structural variances in the dimer-like products. Studies on the transformation of unsubstituted o-(pivaloylaminomethyl)benzaldehyde under similar conditions were presented as well. Keywords: DFT calculations; NMR; reaction mechanism; rearrangement

• case of isoindoles is that the attack of water at cation 19 and subsequent ring opening did not happen here. DFT calculations The proposed mechanism of the 1→2 rearrangement (Scheme 4) was investigated in detail by DFT level quantum chemical computations using the Gaussian 09 program package [19

• ), respectively, was also investigated by DFT level quantum chemical calculations with the same parameters as in the case of the 1→2 rearrangement. The racemic RS and RR forms were taken into consideration, and the computations showed that the formation of the RS compound required an energy investment of ΔG#4e

Azidophosphonium salt-directed chemoselective synthesis of (E)/(Z)-cinnamyl-1H-triazoles and regiospecific access to bromomethylcoumarins from Morita–Baylis–Hillman adducts

• Soundararajan Karthikeyan,
• Radha Krishnan Shobana,
• Kamarajapurathu Raju Subimol,
• J. Helen Ratna Monica and
• Ayyanoth Karthik Krishna Kumar

Beilstein J. Org. Chem. 2020, 16, 1579–1587, doi:10.3762/bjoc.16.130

• initiates the allylic rearrangement and thereby facilitates the removal of the crucial phosphonium oxide. The outcome of this process is the structurally relevant azido moiety IIIa, which then undergoes a 1,3-dipolar cycloaddition with the copper acetylide IVa to furnish the 1,4-disubstituted 1,2,3

Heterogeneous photocatalysis in flow chemical reactors

• Christopher G. Thomson,
• Ai-Lan Lee and
• Filipe Vilela

Beilstein J. Org. Chem. 2020, 16, 1495–1549, doi:10.3762/bjoc.16.125

An overview on disulfide-catalyzed and -cocatalyzed photoreactions

• Yeersen Patehebieke

Beilstein J. Org. Chem. 2020, 16, 1418–1435, doi:10.3762/bjoc.16.118

• give the four-membered ring intermediate 29. Finally, the rearrangement of the four-membered intermediate provides the diketone 30 as the product (Scheme 8). In 2017, Wang and co-workers reported an oxidative cleavage of aromatic alkenes at ambient temperature with visible-light irradiation, using

• generates the active species Mes–Acr–Me*. Then, the single-electron oxidation of the deprotonated carboxylic acid 52 with Mes–Acr–Me* results in the formation of an acyloxyl radical 53. The subsequent rearrangement of the radical 53 gives a carbon-centered radical 54 and carbon dioxide. The phenyl thiyl

Recent synthesis of thietanes

• Jiaxi Xu

Beilstein J. Org. Chem. 2020, 16, 1357–1410, doi:10.3762/bjoc.16.116

• underwent a thermal rearrangement to generate tricyclic isobenzofurans 313 through the ring-cleavage of the thietanes. It was assumed that the rearrangement was assisted through participation of the oxygen lone-pair electrons [17] (Scheme 57). The silicon-containing phenyl triphenylsilyl thioketone (316

• -haloalkyl)thiiranes: A thiirane–thietane rearrangement took place upon the interaction of (1-haloaklyl)thiiranes 398 with hard and weak nucleophiles (:Nu−) in the presence of a base. It was an efficient method for the preparation of 3-substituted thietanes 400 from (1-haloalkyl)thiiranes 398 through an

The charge-assisted hydrogen-bonded organic framework (CAHOF) self-assembled from the conjugated acid of tetrakis(4-aminophenyl)methane and 2,6-naphthalenedisulfonate as a new class of recyclable Brønsted acid catalysts

• Svetlana A. Kuznetsova,
• Alexander S. Gak,
• Yulia V. Nelyubina,
• Vladimir A. Larionov,
• Han Li,
• Michael North,
• Vladimir P. Zhereb,
• Alexander F. Smol'yakov,
• Artem O. Dmitrienko,
• Michael G. Medvedev,
• Igor S. Gerasimov,
• Ashot S. Saghyan and
• Yuri N. Belokon

Beilstein J. Org. Chem. 2020, 16, 1124–1134, doi:10.3762/bjoc.16.99

• nondirectional forces in the crystal whilst leaving the directional hydrogen bonds still present so that the framework remained heterogeneous. Notably, simple organic cages that exhibit guest-induced “breathing” and selective gas separation have been reported [29][39][40][41]. The reversible rearrangement of the

Fluorinated phenylalanines: synthesis and pharmaceutical applications

• Laila F. Awad and
• Mohammed Salah Ayoup

Beilstein J. Org. Chem. 2020, 16, 1022–1050, doi:10.3762/bjoc.16.91

• ‑hydroxy-β-aminophenylalanine esters [75][76] 152a–d using XtalFluor-E. The reaction also included an aziridinium ion rearrangement as the key step. Deprotection of the resultant β-fluoro-α-amino acid esters 153a–d afforded the corresponding enantiopure anti-β-fluorophenylalanines 154a–d in good yield and

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

Recent applications of porphyrins as photocatalysts in organic synthesis: batch and continuous flow approaches

• Rodrigo Costa e Silva,
• Luely Oliveira da Silva,
• Aloisio de Andrade Bartolomeu,
• Timothy John Brocksom and
• Kleber Thiago de Oliveira

Beilstein J. Org. Chem. 2020, 16, 917–955, doi:10.3762/bjoc.16.83

• superoxide radical anion by a reductive quenching and the rearrangement of the hydroperoxide intermediate [41]. The heterogeneous protocol using MOF porphyrins was significantly faster than the corresponding homogeneous photocatalysis, which was attributed to higher photostability of the porphyrins as MOF

• photooxygenation reactions were described using TPP as photocatalyst. We have described a study on endoperoxydations followed by rearrangement to yield naphthoquinones starting from α-naphthols and using porphyrins as photocatalysts (Scheme 36) [23]. Eleven examples were described from mg to g-scale reactions, and

• conditions, a porphyrin-based protocol for endoperoxidation of the diene, followed by the Kornblum–DeLaMare rearrangement and further telescoped transformations. This protocol yields different classes of products such as furans, tropone, diketones and hydroxyenones, all of them starting from the

Aldehydes as powerful initiators for photochemical transformations

• Maria A. Theodoropoulou,
• Nikolaos F. Nikitas and
• Christoforos G. Kokotos

Beilstein J. Org. Chem. 2020, 16, 833–857, doi:10.3762/bjoc.16.76

• -butyl ketone (1) yields acetone (4) and propylene (3). Reaction (2) of Scheme 1 refers to a type II intramolecular rearrangement of crotonaldehyde (5) to 3-butenal (7). The triplet state energy donors were quenched by diacetyl and cis-2-butene. In 1970, Cocivera and Trozzollo studied the photolysis of

Preparation of 2-phospholene oxides by the isomerization of 3-phospholene oxides

• Péter Bagi,
• Réka Herbay,
• Nikolett Péczka,
• Zoltán Mucsi,
• István Timári and
• György Keglevich

Beilstein J. Org. Chem. 2020, 16, 818–832, doi:10.3762/bjoc.16.75

• Analytical Chemistry, University of Debrecen, H-4032 Debrecen, Hungary 10.3762/bjoc.16.75 Abstract A series of 1-substituted-3-methyl-2-phospholene oxides was prepared from the corresponding 3-phospholene oxides by double bond rearrangement. The 2-phospholene oxides could be obtained by heating the 3

• thermal conditions, in the presence of acids or bases or via the formation of chlorophosphonium salts. In our study, the 3-methyl-3-phospholene oxides were considered as model compounds, the double bond rearrangement of a 3-phospholene oxide and a 3,4-dimethyl-3-phospholene oxide was also investigated

• rearrangement, involving zwitterionic structure 11 via high energy and a four-membered ring transition state [TS(1→11)]. This stressed structure has a rigid, entropically unbeneficial transition. The second transition state [TS(11→4)] represents a significantly lower energy gap with a more comfortable five

Combining enyne metathesis with long-established organic transformations: a powerful strategy for the sustainable synthesis of bioactive molecules

• Valerian Dragutan,
• Ileana Dragutan,
• Albert Demonceau and
• Lionel Delaude

Beilstein J. Org. Chem. 2020, 16, 738–755, doi:10.3762/bjoc.16.68

• coordinated to the metallacarbene and cleaved (Scheme 3 (a)) and the formed alkylidene species is inserted into the alkyne unit through a metallacyclobutene intermediate. This metallacyclobutene, through the rearrangement to a vinyl metal-alkylidene (Scheme 3 (b)) and subsequent metathesis with the alkene

• on a Diels–Alder cycloaddition, an intramolecular Mitsunobu reaction, a [3,3]-sigmatropic rearrangement, and a ring-closing metathesis. As an alternative to this approach, Clark et al. [86] efficiently performed a sequential Ru-catalyzed enyne metathesis in combination with a hydroboration, and an

• of cyclopentene-1,4-diol that was obtained by the enzymatic desymmetrization of the corresponding diacetate, an enyne metathesis precursor was accessed by a Mitsunobu-type coupling reaction with propargylic amide. The ring-rearrangement metathesis (RRM) of this enyne precursor was carried out using

Recent advances in Cu-catalyzed C(sp³)–Si and C(sp³)–B bond formation

• Balaram S. Takale,
• Ruchita R. Thakore,
• Elham Etemadi-Davan and
• Bruce H. Lipshutz

Beilstein J. Org. Chem. 2020, 16, 691–737, doi:10.3762/bjoc.16.67

• rearrangement to form a C–Cu bond-containing intermediate 78 (Scheme 17A). The O–Cu intermediate 77 can be intercepted either by PhMe2SiBpin or methanol to give the silylated O-Bpin product 79 or silyl alcohol 80, respectively. Interestingly, it was eventually realized that the use of the NHC ligand is not

• intermediate. This species then undergoes [3,3]-sigmatropic rearrangement, positioning the allylic unit in a regio- and stereospecific manner, along with rearomatization to afford the products 357–360 (Scheme 57) [107]. The borylfluoromethylation of acrylamides, acrylates, and heteroaromatic-substituted alkenes

• was observed. Due to the possibility of facile rearrangement of the former to the latter, it could not be concluded that a direct insertion of the aldehyde into the Cu–B bond is taking place. The enantioselective borylation of aliphatic aldehydes 448 was first reported in 2015 using CuCl/KO-t-Bu/(R

Synthesis of C₇₀-fragment buckybowls bearing alkoxy substituents

• Yumi Yakiyama,
• Shota Hishikawa and
• Hidehiro Sakurai

Beilstein J. Org. Chem. 2020, 16, 681–690, doi:10.3762/bjoc.16.66

• and optical properties were investigated by single crystal X-ray analysis and UV–vis spectroscopy. In the synthesis of dioxole derivative 5b, the regioisomer 5c was also produced. The yield of 5c was increased by increasing the reaction temperature, indicating that the rearrangement might involve the

• equilibrium between the Pd(IV) intermediates through C–H bond activation. Keywords: buckybowl; C70; rearrangement through C–H bond activation; Introduction The study of buckybowls, the bowl-shaped π-conjugated aromatic hydrocarbons corresponding to the fragments of fullerenes, pioneered by the works on

• expansion by Wagner–Meerwein rearrangement, followed by Pd-catalyzed annulation (Figure 1) [18]. An UV–vis spectroscopy study revealed that the electronic character of 1 rather resembled that of an indenopyrene moiety than that of benzopyrene. Our synthetic route allows to easily introduce substituents on

Regio- and stereoselective synthesis of new ensembles of diversely functionalized 1,3-thiaselenol-2-ylmethyl selenides by a double rearrangement reaction

• Svetlana V. Amosova,
• Andrey A. Filippov,
• Nataliya A. Makhaeva,
• Alexander I. Albanov and
• Vladimir A. Potapov

Beilstein J. Org. Chem. 2020, 16, 515–523, doi:10.3762/bjoc.16.47

• potassium selenocyanate proceeded via a rearrangement with ring expansion, leading to a six-membered 2,3-dihydro-1,4-thiaselenin-2-yl selenocyanate (kinetic product) which in turn underwent rearrangement with ring contraction to a 1,3-thiaselenol-2-ylmethyl selenocyanate (thermodynamic product). These

• -thiaselenole; nucleophilic addition; nucleophilic substitution; rearrangement; seleniranium intermediate; Introduction The regio- and stereoselective synthesis of organoselenium compounds based on selenium-centered electrophilic reagents has been one of the most important and effective directions in

• -dihydro-1,4-thiaselenines (up to 96% yields) – products of rearrangement with ring expansion, which in turn underwent rearrangement with ring contraction, forming a new family of 1,3-thiaselenoles in up to 99% yield. The article was included in the RSC themed web collection "The chemistry of Selenium

KOt-Bu-promoted selective ring-opening N-alkylation of 2-oxazolines to access 2-aminoethyl acetates and N-substituted thiazolidinones

• Qiao Lin,
• Shiling Zhang and
• Bin Li

Beilstein J. Org. Chem. 2020, 16, 492–501, doi:10.3762/bjoc.16.44

• nitrogen to benzyl bromide would form an ammonium intermediate C. The final product 3a would be produced after rearrangement and release of tert-butyl bromide. On the other hand, added I2 would react with intermediate B’ and lead to the thiazolidone compound 5a. Conclusion In summary, we have developed a

Recent advances in photocatalyzed reactions using well-defined copper(I) complexes

• Mingbing Zhong,
• Xavier Pannecoucke,
• Philippe Jubault and
• Thomas Poisson

Beilstein J. Org. Chem. 2020, 16, 451–481, doi:10.3762/bjoc.16.42

• -photocatalyzed intramolecular decarboxylative C–N coupling of NHP esters using an in situ-formed heteroleptic copper complex (Scheme 23) [38]. This protocol, a versatile alternative to the Curtius rearrangement, was applied to a large variety of substrates, including primary/secondary alkyl, cycloalkyl, and

Six-fold C–H borylation of hexa-peri-hexabenzocoronene

• Mai Nagase,
• Kenta Kato,
• Akiko Yagi,
• Yasutomo Segawa and
• Kenichiro Itami

Beilstein J. Org. Chem. 2020, 16, 391–397, doi:10.3762/bjoc.16.37

• functionalizing poorly soluble compounds, functionalized HBC is typically synthesized by dehydrogenative cyclization, which is called Scholl reaction, of precursors having solubilizing substituents [12][13]. However, the Scholl reaction sometimes causes unexpected rearrangement such as 1,2-aryl shift, and