Asymmetric synthesis of tertiary thiols and thioethers

• Jonathan Clayden and
• Paul MacLellan

Beilstein J. Org. Chem. 2011, 7, 582–595, doi:10.3762/bjoc.7.68

• opening of epoxides in hindered systems [18][19][20][21][22][23], with most examples of the latter occurring at quaternary carbon atoms which are part of ring systems [18][19][20][21][22], and in particular in steroids [18][19][20]. For example, the thiol-containing androgen 19 is prepared in 71% yield by

Oxidative allylic rearrangement of cycloalkenols: Formal total synthesis of enantiomerically pure trisporic acid B

• Silke Dubberke,
• Muhammad Abbas and
• Bernhard Westermann

Beilstein J. Org. Chem. 2011, 7, 421–425, doi:10.3762/bjoc.7.54

• resolution; natural products; oxidative rearrangement; pig liver esterase (PLE); trisporic acid B; Introduction The generation of chiral, non-racemic compounds bearing a stereogenic quaternary carbon centre is of great interest [1][2][3][4][5][6][7][8]. Therefore, much effort has been directed towards the

Recent advances in carbocupration of α-heterosubstituted alkynes

• Ahmad Basheer and
• Ilan Marek

Beilstein J. Org. Chem. 2010, 6, No. 77, doi:10.3762/bjoc.6.77

• α-alkoxyalkynes. Carbocupration of substituted α-alkoxyalkynes. Formation of the branched isomer. Formation of the linear isomer. Carbocupration of O-alkynyl carbamates. Carbocupration of ynamines. Carbocupration of ynamide. Formation of aldol products possessing stereogenic quaternary carbon

Shelf-stable electrophilic trifluoromethylating reagents: A brief historical perspective

• Norio Shibata,
• Andrej Matsnev and
• Dominique Cahard

Beilstein J. Org. Chem. 2010, 6, No. 65, doi:10.3762/bjoc.6.65

• ]thiophenium salts have also demonstrated high ability for trifluoromethylation of β-ketoesters and dicyanoalkylidenes to yield the trifluoromethylated products with a quaternary carbon center, even if the substrates have a rather unreactive acyclic system. In this review, we wish to briefly provide a

Synthesis of (3R,5R)-harzialactone A and its (3R,5S)-isomer

• Gowravaram Sabitha,
• Rangavajjula Srinivas,
• Sukant K. Das and
• Jhillu S. Yadav

Beilstein J. Org. Chem. 2010, 6, No. 8, doi:10.3762/bjoc.6.8

• quaternary carbon in the downfield region (98.7 ppm). Deprotection of the benzyl group using Li/liq. NH3 gave alcohol 10. Oxidation of alcohol 10 under Swern conditions and further oxidation of the resulting aldehyde using NaH2PO4, NaClO2 in DMSO/H2O furnished the target hydroxylactone (3R,5R)-1 as reported

• confirms the presence of δ-lactone in (3R,5S)-2. The anti relationship of two hydroxyl groups was studied in compound 12. In the 13C NMR of 12, the acetonide methyl groups resonated at 24.9 and 34.2 ppm indicating a 1,3-anti-relationship that was further substantiated by the appearance of the quaternary

• carbon in the downfield region (100.5 ppm) [7]. In conclusion, a stereoselective synthesis of natural (+)-(3R,5R)-harzialactone A and its nonnatural stereoisomer (3R,5S) has been accomplished. Natural harzialactone A (1), and its (3R,5S)-isomer (2). Retrosynthesis of harzialactone A (1). Synthesis of

A review of new developments in the Friedel–Crafts alkylation – From green chemistry to asymmetric catalysis

• Magnus Rueping and
• Boris J. Nachtsheim

Beilstein J. Org. Chem. 2010, 6, No. 6, doi:10.3762/bjoc.6.6

• formation of a quaternary carbon atom was possible. Although the product was isolated in lower yields (Scheme 17). Subsequently this method was expanded to other nucleophiles, such as 1,3-diketones [60]. Mirroring the Bi(OTf)3-catalyzed method, Hua et al. developed a BiCl3-catalyzed synthesis of 1,1

The development and evaluation of a continuous flow process for the lipase- mediated oxidation of alkenes

• Charlotte Wiles,
• Marcus J. Hammond and
• Paul Watts

Beilstein J. Org. Chem. 2009, 5, No. 27, doi:10.3762/bjoc.5.27

• obtained were consistent with the literature. The following abbreviations are used to report NMR spectroscopic data; s = singlet, d = doublet, t = triplet, br s = broad singlet, q = quartet, dd = double doublet, dt = doublet of triplets, m = multiplet and C0 = quaternary carbon. Analysis of samples by Gas

Synthesis of new C^α-tetrasubstituted α-amino acids

• Andreas A. Grauer and
• Burkhard König

Beilstein J. Org. Chem. 2009, 5, No. 5, doi:10.3762/bjoc.5.5

• aryl group [3][4]. These building blocks if compared to natural α-amino acids show more constrained conformations and are stereochemically stable due to the quaternary carbon centre [5]. By the use of such amino acids, even short peptide sequences can be made to adopt stable secondary structures like β

Cimicifoetisides A and B, two cytotoxic cycloartane triterpenoid glycosides from the rhizomes of Cimicifuga foetida, inhibit proliferation of cancer cells

• Li-Rong Sun,
• Chen Qing,
• Yan-Li Zhang,
• Shu-Yu Jia,
• Zhong-Rong Li,
• Shen-Ji Pei,
• Ming-Hua Qiu,
• Michael L. Gross and
• Samuel X. Qiu

Beilstein J. Org. Chem. 2007, 3, No. 3, doi:10.1186/1860-5397-3-3

• the triterpene aglycone. A characteristic ketalic quaternary carbon signal was observed at δC 112.0 (s, C-16) together with two oxygen-bearing methine signals at δC 80.3 (d, C-15) and 90.2 (d, C-24). Two carbons were assigned to an acetyl group [δC 170.2 and 21.4], and these spectra also showed a set

• methylene signals (δH 0.22 and 0.46) and the methylene carbons at δC 32.3 (C-1) and δC 26.3 (C-11), a methylene carbon at δC 48.7 (C-8); between H-3 (δH 3.44) and methyl carbon signals at δC 25.4 (C-29) and δC 15.3 (C-30); between H-23 (δH 4.75) and the quaternary carbon signal at δC 112.0 (C-16); between H

• -24 (δH 3.77) and the quaternary carbon signals at δC 112.0 (C-16) and δC 71.0 (C-25), the methine carbon signal at δC 71.3 (C-23), the methylene carbon signal at δC 38.2 (C-22) and the methyl carbon signals at δC 27.2 (C-26) and 25.4 (C-27). Additionally, the methyl signals at δH 1.44 (Me-26)/δH 1.47