Synthesis of alkynyl-substituted camphor derivatives and their use in the preparation of paclitaxel-related compounds

• M. Fernanda N. N. Carvalho,
• Rudolf Herrmann and
• Gabriele Wagner

Beilstein J. Org. Chem. 2017, 13, 1230–1238, doi:10.3762/bjoc.13.122

• formed propargyl group is isomerized to an allene moiety, obviously due to the excess of the strongly basic lithium salt [35]. This unexpected monosubstitution remains unexplained and is not applicable as basis for a general selective synthesis of monoalkynylcamphor derivatives. Alkynes can also be

Nucleophilic and electrophilic cyclization of N-alkyne-substituted pyrrole derivatives: Synthesis of pyrrolopyrazinone, pyrrolotriazinone, and pyrrolooxazinone moieties

• Işıl Yenice,
• Sinan Basceken and
• Metin Balci

Beilstein J. Org. Chem. 2017, 13, 825–834, doi:10.3762/bjoc.13.83

• formation of 12d. Since the central carbon atom of an allene unit is more electropositive, the carbon atom can undergo an attack by the amide nitrogen atom to form a six-membered ring. In the case of 7a–c, the formation of allenic intermediates is out of question [15]. Based on our experimental results, we

• and methylene protons in 13c and 16 with the relevant carbon atoms (from the HMBC spectrum). Single-crystal X-ray structure of 12c shown with 40% probability displacement ellipsoids. The structure of allene 17 formed during the reaction of 7d with a base. Single-crystal X-ray structure of 19c shown

Unusual reactions of diazocarbonyl compounds with α,β-unsaturated δ-amino esters: Rh(II)-catalyzed Wolff rearrangement and oxidative cleavage of N–H-insertion products

• Valerij A. Nikolaev,
• Jury J. Medvedev,
• Olesia S. Galkina,
• Ksenia V. Azarova and
• Christoph Schneider

Beilstein J. Org. Chem. 2016, 12, 1904–1910, doi:10.3762/bjoc.12.180

• colleagues showed that similar reactions can be extended to compounds with triple bonds and allene fragments [14]. Recently we have shown that the catalytic decomposition of diazomalonates and other diazoesters using Rh(II)- and Cu(II)-complexes in the presence of α,β-unsaturated δ-(N-aryl)amino esters 1

Modular synthesis of the pyrimidine core of the manzacidins by divergent Tsuji–Trost coupling

• Sebastian Bretzke,
• Stephan Scheeff,
• Felicitas Vollmeyer,
• Friederike Eberhagen,
• Frank Rominger and
• Dirk Menche

Beilstein J. Org. Chem. 2016, 12, 1111–1121, doi:10.3762/bjoc.12.107

• imines, carbonyls or allene homologs. The resulting homologated nucleophile 8 may then be trapped in an intramolecular fashion by a π-allyl complex, which may concomitantly form from 6 through activation of the homoallylic functionality with a suitable transition metal catalyst. According to this concept

Catalytic asymmetric synthesis of biologically important 3-hydroxyoxindoles: an update

• Bin Yu,
• Hui Xing,
• De-Quan Yu and
• Hong-Min Liu

Beilstein J. Org. Chem. 2016, 12, 1000–1039, doi:10.3762/bjoc.12.98

• corresponding products were found to have improved diastereoselectivities. Phenols with electron-withdrawing groups failed to afford the expected products under the same conditions. Mechanistically, Ga(OTf)3 may activate the allene and phenol substrates simultaneously via the bidentate model. In contrast, the

• spirocyclic 2,5-dihydrofuran was obtained in 98% yield when the π acid AuCl3 (5 mol %) was used. AuCl3 may coordinate one of the allene double bonds via a monodentate model. The phenol substrate did not participate in this reaction. In 2013, Ji and co-workers described the I2-catalyzed construction of pyrrolo

Solving the puzzling competition of the thermal C²–C⁶ vs Myers–Saito cyclization of enyne-carbodiimides

• Anup Rana,
• Mehmet Emin Cinar,
• Debabrata Samanta and
• Michael Schmittel

Beilstein J. Org. Chem. 2016, 12, 43–49, doi:10.3762/bjoc.12.6

• approach for the diradical species and the transition states (TSs) connecting them while the restricted method was used for closed shell species. The BLYP functional was chosen for computation because the benchmark studies done by Schreiner showed good applicability of BLYP for the enyne-allene system [3

Recent applications of ring-rearrangement metathesis in organic synthesis

• Sambasivarao Kotha,
• Milind Meshram,
• Priti Khedkar,
• Shaibal Banerjee and
• Deepak Deodhar

Beilstein J. Org. Chem. 2015, 11, 1833–1864, doi:10.3762/bjoc.11.199

• /allene cycloaddition, discovered by Himbert and Henn were found to undergo a RRM in a facile manner in the presence of catalyst 6 to produce complex polycyclic lactams. In this regard, the required building block 319 was obtained from compound 318 by cycloaddition reaction. A variety of complex molecular

Reaction of allene esters with Selectfluor/TMSX (X = I, Br, Cl) and Selectfluor/NH₄SCN: Competing oxidative/electrophilic dihalogenation and nucleophilic/conjugate addition

• A. Srinivas Reddy and
• Kenneth K. Laali

Beilstein J. Org. Chem. 2015, 11, 1641–1648, doi:10.3762/bjoc.11.180

• additions in halofunctionalization with TMSX/Selectfluor and thiocyanation reactions with NH4SCN/Selectfluor. These competing pathways are influenced by the nature of the anion, allene structure, and the choice of solvent. Keywords: allene esters; oxidative electrophilic dihalogenation/conjugate addition

• order to examine a possible influence of the structure of the allenoate on the product distribution, allene esters 2–6 were synthesized (Figure 1). The reactions of ethyl allenoate (2) with TMSBr, TMSI and with NH4SCN were studied in the presence of Selectfluor in MeCN and DMF (Scheme 5). With TMSBr and

• , especially in reactions with TMSI/Selectfluor (see Scheme 10), appears consistent with stabilization of the incipient allenyl cation in the oxidative/electrophilic pathway. Allene esters synthesized for this study. Reaction of benzyl allenoate (1) with TMSBr with and without Selectfluor (E/Z designations, as

Why base-catalyzed isomerization of N-propargyl amides yields mostly allenamides rather than ynamides

• Armando Navarro-Vázquez

Beilstein J. Org. Chem. 2015, 11, 1441–1446, doi:10.3762/bjoc.11.156

• propargyl bromide (Scheme 1) [6][7]. Subsequent base-catalyzed isomerization of N-propargyl compound 2 leads to allenamide 3. Whereas in some particular cases the reaction leads to the final N-alkynyl product, in most cases, the reaction stops at the allene stage and does not further progress even when

Synthesis of γ-hydroxypropyl P-chirogenic (±)-phosphorus oxide derivatives by regioselective ring-opening of oxaphospholane 2-oxide precursors

• Iris Binyamin,
• Shoval Meidan-Shani and
• Nissan Ashkenazi

Beilstein J. Org. Chem. 2015, 11, 1332–1339, doi:10.3762/bjoc.11.143

• may possess further functionalities in addition to the phosphorus center such as the γ-hydroxypropyl group which results from the ring opening and π-donor moieties such as aryl, allyl, propargyl and allene which originates from the Grignard reagent. Keywords: chirogenic phosphorus; Grignard reagents

• . Further heating did not provide higher conversion. Following hydrolytic work-up and flash chromatographic purification the product was identified as allene 5f, rather than acetylene 5h, due to propargyl–allene rearrangement (Scheme 5). Most characteristic are the 13C NMR chemical shift of HC=C=CR at

• formed regioselectivly. Synthesis of acetylene and allene phosphine oxides. Synthesis of γ-hydroxypropyl (±)-phosphinatesa and related compounds. Synthesis of γ-hydroxypropyl (±)-phosphine oxidesa. Supporting Information Supporting Information File 66: Experimental details, characterization data and 1H

Selected synthetic strategies to cyclophanes

• Sambasivarao Kotha,
• Mukesh E. Shirbhate and
• Gopalkrushna T. Waghule

Beilstein J. Org. Chem. 2015, 11, 1274–1331, doi:10.3762/bjoc.11.142

• reacted with azetidine-2,3-diones 176 under eco-friendly reaction conditions to generate bis(allene) 177. Compound 177 was then converted into bis(dihydrofuran) 178 by using AuCl3. Macrocyclization of 178 was carried out by using a Ru(II) or Ru(III) catalyst to generate 179 as a mixture of E/Z isomers

Novel carbocationic rearrangements of 1-styrylpropargyl alcohols

• Christine Basmadjian,
• Fan Zhang and
• Laurent Désaubry

Beilstein J. Org. Chem. 2015, 11, 1017–1022, doi:10.3762/bjoc.11.114

• be envisioned that this compound results from the rearrangement of an allene oxide (Scheme 5). Interestingly the dipropargylic alcohol 9 afforded the rearranged allylic ether 20 as the only isolated product (entry 6, Table 1). In order to improve the yields of these reactions and gain insight in the

Chiroptical properties of 1,3-diphenylallene-anchored tetrathiafulvalene and its polymer synthesis

• Masashi Hasegawa,
• Junta Endo,
• Seiya Iwata,
• Toshiaki Shimasaki and
• Yasuhiro Mazaki

Beilstein J. Org. Chem. 2015, 11, 972–979, doi:10.3762/bjoc.11.109

• , Chiba 275-0016, Japan 10.3762/bjoc.11.109 Abstract A novel tetrathiafulvalene dimer, bridged by a chiral 1,3-diphenylallene framework, has been prepared as an optically active compound having strong chiroptical properties. Although a chiral allene bearing strong electron-donating group(s) often

• undergoes slow photoracemization even in daylight, the present allene is totally configurationally stable under ordinary conditions. Each isomer possesses pronounced chiroptical properties in its ECD spectra reflecting the chiral allene framework. Moreover, the elongation of the chiral main chain was also

• carried out by direct C–H activation of the TTF unit, and the chiroptical properties of the resulting polymer were also investigated. Keywords: allene; axial chirality; chiroptical properties; redox; tetrathiafulvalene; Introduction Recently, there has been a growing interest in chiral π-conjugated

Anionic sigmatropic-electrocyclic-Chugaev cascades: accessing 12-aryl-5-(methylthiocarbonylthio)tetracenes and a related anthra[2,3-b]thiophene

• Laurence Burroughs,
• John Ritchie,
• Mkhethwa Ngwenya,
• Dilfaraz Khan,
• William Lewis and
• Simon Woodward

Beilstein J. Org. Chem. 2015, 11, 273–279, doi:10.3762/bjoc.11.31

• , stepwise synthesis of a family of acene derivatives from various acyclic precursors is normally very step intensive. The prevalence of these issues in the synthesis of substituted tetracenes caused Lin [14], building on the anthracycline natural product work of Saá [15], to introduce a 1,2-bis-allene

• and the mixture allowed to come to ambient temperature. This resulted in the smooth formation of allene 14. In particular, the presence of allenic and C=O signals in the 13C NMR spectrum at 212.1 and 188.5 ppm and the absence of any alkyne C≡C resonances in the region δC 80–90 are indicative of this

• rapid access to mono sulfur-containing acenes, and is applicable to small scale library synthesis. Only low cost reagents are required and otherwise difficult to synthesise hindered 1,3,4,12-tetrasubstituted species can be made straightforwardly. Use of bis-allene intermediates 2 for rapid access to

2-(1-Hydroxypropyn-2-yl)-1-vinylpyrroles: the first successful Favorsky ethynylation of pyrrolecarbaldehydes

• A. V. Ivanov,
• V. S. Shcherbakova,
• I. A. Ushakov,
• L. N. Sobenina,
• O. V. Petrova,
• A. I. Mikhaleva and
• B. A. Trofimov

Beilstein J. Org. Chem. 2015, 11, 228–232, doi:10.3762/bjoc.11.25

• acetylene–allene isomerization of the secondary acetylenic alcohols 2a–j formed. The reaction is carried out at atmospheric pressure (acetylene flow, 7–10 °C, 2–4 h). The yields of hydroxypropynylpyrroles 2a–j range from 53–94% (Table 1). The reaction was monitored by GLC and was stopped after complete

• of isolated yields is attributable not only to the difference in the reactivity of aldehydes 1a–j, but also to the propensity of the product to undergo acetylene–allene isomerization to give the polymerizable vinyl ketones [21]. As seen from Table 1, the reaction tolerates a wide scope of pyrrole-2

Chiral phosphines in nucleophilic organocatalysis

• Yumei Xiao,
• Zhanhu Sun,
• Hongchao Guo and
• Ohyun Kwon

Beilstein J. Org. Chem. 2014, 10, 2089–2121, doi:10.3762/bjoc.10.218

• electron-deficient imines with allenes. On the other hand, the rigid bridged [2.2.1] bicyclic chiral phosphine A3 appears to be an excellent catalyst for allene/imine [3 + 2] annulation. With a chiral phosphine-catalyzed [3 + 2] annulation of an indole-derived imine and an γ-ethylallenoate as the key step

• , Lu and co-workers explored imine–allene [3 + 2] annulations catalyzed by a dipeptide-derived phosphine [68]. They identified the phosphine H12, a close analogue of H10, as the most suitable catalyst. In the presence of 5 mol % of H12, a wide range of alkylimines and various arylimines could be

Sacrolide A, a new antimicrobial and cytotoxic oxylipin macrolide from the edible cyanobacterium Aphanothece sacrum

• Naoya Oku,
• Miyako Matsumoto,
• Kohsuke Yonejima,
• Keijiroh Tansei and
• Yasuhiro Igarashi

Beilstein J. Org. Chem. 2014, 10, 1808–1816, doi:10.3762/bjoc.10.190

• should be routed through α-linolenic acid-derived allene oxide (Scheme 3) [16]. The addition of H2O to this intermediate gives α,β-unsaturated-γ-ketol, which accepts further oxidation at the α'-position, and macrolactonization of the resulting α',γ-ketodiol would yield 1. Similar, but rather simpler

• metabolites were found from corn [17][18]. However, they comprise a pair of enantiomers and thus should be generated non-enzymatically from α-linoleic acid-derived allene oxide. In contrast, 1 is optically active and is more likely to be produced by a sequence of enzymatic reactions. Sacrolide A (1) inhibited

Synthesis of rigid p-terphenyl-linked carbohydrate mimetics

• Maja Kandziora and
• Hans-Ulrich Reissig

Beilstein J. Org. Chem. 2014, 10, 1749–1758, doi:10.3762/bjoc.10.182

• -allene. The Lewis acid-induced rearrangement of this heterocycle provided the corresponding bicyclic 1,2-oxazine derivative that may be regarded as internally protected amino sugar analogue. After subsequent reduction of the carbonyl group, the resulting bicyclic compound was used for Suzuki cross

• ]-cyclization of D-isoascorbic acid-derived (Z)-nitrone 6 and lithiated TMSE-allene 5. Results and Discussion For our synthesis of new divalent carbohydrate mimetics we required 1,2-oxazine derivatives derived from (Z)-nitrone 6 and lithiated alkoxyallenes. The 4-bromophenyl group should allow transition metal

• observed. Due to the complexation of lithiated allene 9 to the nitrone 6 an exclusive formation of the two syn-1,2-oxazines 4 was observed. This result suggests that the configuration at C-2 of the dioxolane moiety has no influence on the stereochemical outcome of the reaction. The model suggested by

Multicomponent reactions in nucleoside chemistry

• Mariola Koszytkowska-Stawińska and
• Włodzimierz Buchowicz

Beilstein J. Org. Chem. 2014, 10, 1706–1732, doi:10.3762/bjoc.10.179

• nucleosides 93 were also prepared by this method. 7. The carbopalladation of dienes A reaction of an aryl halide, an unsaturated alkene (diene, allene), and an amine catalyzed by Pd(0) species, referred to as carbopalladation of dienes, results in the three-component assembly of an unsaturated amine (Scheme

4-Hydroxy-6-alkyl-2-pyrones as nucleophilic coupling partners in Mitsunobu reactions and oxa-Michael additions

• Michael J. Burns,
• Thomas O. Ronson,
• Richard J. K. Taylor and
• Ian J. S. Fairlamb

Beilstein J. Org. Chem. 2014, 10, 1159–1165, doi:10.3762/bjoc.10.116

• methodology, we explored the addition of hydroxypyrones to both an allene and an internal alkyne to furnish a trisubstituted enol ether. Addition of 4-hydroxy-6-methyl-2-pyrone (3a) to the terminal allene 8 under the optimised conditions proceeded smoothly to give the trans-trisubstituted enol ether 9 in 52

• desired product. The phacelocarpus 2-pyrones 1 and 2. Generalised O-functionalisation of 6-alkyl-4-hydroxy-2-pyrones 3. Synthesis of alkylated 2-pyrones 3b–e. Michael addition of 3a to allene 8 and internal alkyne 10. Synthesis of 2-pyronyl ethers 4a–l. Michael addition reaction optimisation. Synthesis of

Allenylphosphine oxides as simple scaffolds for phosphinoylindoles and phosphinoylisocoumarins

• G. Gangadhararao,
• Ramesh Kotikalapudi,
• M. Nagarjuna Reddy and
• K. C. Kumara Swamy

Beilstein J. Org. Chem. 2014, 10, 996–1005, doi:10.3762/bjoc.10.99

• the interemdiate allene [29]. Many other unusual transformations have also been reported recently [31]. In another reaction leading to phosphinoylindenone depicted in Scheme 1c, an intramolecular ene-reaction is possibly involved and in Scheme 1d the reaction led to phosphinoylisochromenes via

• deprotection of an allene intermediate under Lewis acid mediation [22]. In this context it was of interest to see, in a reaction like that shown in Scheme 1c, whether the introduction of an amide or a carboxylate ester in place of the –CHO group could lead to phosphinoyl-subtstituted indoles/isocoumarins via

• formed (Scheme 3). The presence of a doublet for PCH carbon at δ 48.3 with a 1J(P–C) value of 62.0 Hz reveals that the phosphorus moiety is attached to an sp3-hybridized carbon. On the other hand, in the reaction using the =CHMe allene 3m, two isomers in which the N–H proton moves to either the α-carbon

Silver and gold-catalyzed multicomponent reactions

• Giorgio Abbiati and
• Elisabetta Rossi

Beilstein J. Org. Chem. 2014, 10, 481–513, doi:10.3762/bjoc.10.46

• dealing with the use of BINAP–AgClO4 as a chiral catalyst in the same two-component reaction [98]. Higher enantioselectivities were rarely observed with SbF6− being the weaker coordinating counter ion. An interesting application of silver catalysis in the allene chemistry field has been recently proposed

• [2 + 2 + 1] cycloaddition of allenoates 84, dual activated olefins 85, and isocyanides 83 (Scheme 39). It is noteworthy, that only the external double bond of the allenic fragment is embedded in the final carbocyclic ring, whereas in the phosphine-catalyzed [3 + 2] cycloadditon process the allene

The Flögel-three-component reaction with dicarboxylic acids – an approach to bis(β-alkoxy-β-ketoenamides) for the synthesis of complex pyridine and pyrimidine derivatives

• Mrinal K. Bera,
• Moisés Domínguez,
• Paul Hommes and
• Hans-Ulrich Reissig

Beilstein J. Org. Chem. 2014, 10, 394–404, doi:10.3762/bjoc.10.37

• – discovered and mechanistically elucidated by Oliver Flögel – features a three-component reaction that employs alkoxyallenes, nitriles and carboxylic acids: upon treatment with n-butyllithium the allene is lithiated in α-position to the alkoxy moiety; the addition of a nitrile as electrophile to this highly

Synthesis of new enantiopure poly(hydroxy)aminooxepanes as building blocks for multivalent carbohydrate mimetics

• Léa Bouché,
• Maja Kandziora and
• Hans-Ulrich Reissig

Beilstein J. Org. Chem. 2014, 10, 213–223, doi:10.3762/bjoc.10.17

• enantiopure nitrones and lithiated TMSE-allene we prepared three 1,2-oxazine derivatives which underwent a highly stereoselective Lewis acid-induced rearrangement to give bicyclic products in good yield. Subsequent reductive transformations delivered a library of new poly(hydroxy)aminooxepane derivatives. The

• ]. The general approach is shown in Scheme 1: the chiral pool-derived nitrones A [29][30] undergo a [3 + 3]-cyclization with lithiated [2-(trimethylsilyl)ethoxy]allene (TMSE-allene) [31] as C-3 building block [32] to form the 3,6-dihydro-2H-1,2-oxazines B; subsequent Lewis acid-promoted reactions [23

• a Dondoni protocol [29]. This route allows the synthesis of enantiopure nitrone 3 in multi-gram scale. The enantiopure (Z)-configured nitrones 6, 8 and 3 were treated with in situ lithiated TMSE-allene at −78 °C furnishing the expected 1,2-oxazines syn-7 [37], syn-9 and syn-10 in high yields and

Garner’s aldehyde as a versatile intermediate in the synthesis of enantiopure natural products

• Mikko Passiniemi and
• Ari M.P. Koskinen

Beilstein J. Org. Chem. 2013, 9, 2641–2659, doi:10.3762/bjoc.9.300

• adduct in a good yield. We then turned to the lithiated nucleophile 31. In THF at −78 °C high diastereoselectivity (15:1 anti/syn) was obtained. Unfortunately, direct reduction of 32 to 59 produced allene as a byproduct, which forced us to modify the synthetic route. We have also successfully used (Z