Asymmetric allylic alkylation of Morita–Baylis–Hillman carbonates with α-fluoro-β-keto esters

• Lin Yan,
• Zhiqiang Han,
• Bo Zhu,
• Caiyun Yang,
• Choon-Hong Tan and
• Zhiyong Jiang

Beilstein J. Org. Chem. 2013, 9, 1853–1857, doi:10.3762/bjoc.9.216

• nucleophiles, have been successfully developed. A series of important fluorinated adducts, with chiral quaternary carbon centres containing a fluorine atom, was achieved in good yields (up to 93%), with good to excellent enantioselectivities (up to 96% ee) and moderate diastereoselectivities (up to 4:1 dr

• enantioselectivities [38]. Notably, the reaction between an achiral fluorocarbon nucleophile with MBH carbonates, to afford compounds with chiral quaternary carbon centres bearing a fluorine atom, remains a formidable task. Since 2009, we developed a highly enantioselective and diastereoselective guanidine-catalyzed

• compounds with chiral quaternary carbon centres containing a fluorine atom. Results and Discussion In the preliminary experiments, we investigated the reaction of α-fluoro-β-ketoester 1a with MBH carbonate 2a as the model substrate, in the presence of several commercially available Cinchona alkaloids as

Organocatalyzed enantioselective desymmetrization of aziridines and epoxides

• Ping-An Wang

Beilstein J. Org. Chem. 2013, 9, 1677–1695, doi:10.3762/bjoc.9.192

• producing γ-amino acid derivatives with one stereogenic quaternary carbon has been independently developed by Dixon [42] and Jørgensen’s group [43]. Dixon and co-workers discovered that OC-16 bearing bulky substituents both on the 9-O atom and the bridgehead nitrogen afforded excellent enantioselectivity of

A construction of 4,4-spirocyclic γ-lactams by tandem radical cyclization with carbon monoxide

• Mitsuhiro Ueda,
• Yoshitaka Uenoyama,
• Nozomi Terasoma,
• Shoko Doi,
• Shoji Kobayashi,
• Ilhyong Ryu and
• John A. Murphy

Beilstein J. Org. Chem. 2013, 9, 1340–1345, doi:10.3762/bjoc.9.151

• ; iodoaryl allyl azides; tandem radical cyclization; Introduction 4,4-Spirocyclic oxindole γ-lactams containing a quaternary carbon center are key structures for the synthesis of biologically active natural products and the related analogues [1][2][3][4]. Therefore, the development of an efficient synthesis

Lanostane- and cycloartane-type triterpenoids from Abies balsamea oleoresin

• Serge Lavoie,
• Charles Gauthier,
• Jean Legault,
• Sylvain Mercier,
• Vakhtang Mshvildadze and
• André Pichette

Beilstein J. Org. Chem. 2013, 9, 1333–1339, doi:10.3762/bjoc.9.150

• methylene and three sp3 methine groups, three sp3 quaternary carbon atoms, one sp2 methylene and three sp2 methine groups, and seven sp2 quaternary carbon atoms. A 1H–1H COSY experiment provided correlations from H2-1 to H2-2, H-6 to H-5 and H-7, H2-11 to H-9 and H2-12, H2-15 to H2-16 and H-20 to H3-21 and

Cascade radical reaction of substrates with a carbon–carbon triple bond as a radical acceptor

• Hideto Miyabe,
• Ryuta Asada and
• Yoshiji Takemoto

Beilstein J. Org. Chem. 2013, 9, 1148–1155, doi:10.3762/bjoc.9.128

• stereoselectively. Particularly, the substrate 16 having a phenyl group gave the intermediate linear π-radical. Thus, the capture of linear vinyl radical with atom-transfer reagent would be influenced by the steric hindrance around the quaternary carbon atom [43]. Conclusion We have shown the cascade radical

Asymmetric synthesis of a highly functionalized bicyclo[3.2.2]nonene derivative

• Toshiki Tabuchi,
• Daisuke Urabe and
• Masayuki Inoue

Beilstein J. Org. Chem. 2013, 9, 655–663, doi:10.3762/bjoc.9.74

• synthesis; C2-symmetry; catalysis; Diels–Alder reaction; Lewis acid; natural product; quaternary carbon; Introduction Ryanodine (Scheme 1) [1][2][3] is a potent modulator of the intracellular calcium release channels, known as ryanodine receptors [4][5]. Its complex architecture, including eight contiguous

Palladium-catalyzed dual C–H or N–H functionalization of unfunctionalized indole derivatives with alkenes and arenes

• Gianluigi Broggini,
• Egle M. Beccalli,
• Andrea Fasana and
• Silvia Gazzola

Beilstein J. Org. Chem. 2012, 8, 1730–1746, doi:10.3762/bjoc.8.198

• elimination. Palladium–pyridine systems were subsequently investigated with chiral ligands to catalyze enantioselective processes involving alkenylindoles. Several enantioselective indole annulations with formation of a stereogenic quaternary carbon atom were performed by using chiral oxazoline ligands with

Carbohydrate-auxiliary assisted preparation of enantiopure 1,2-oxazine derivatives and aminopolyols

• Marcin Jasiński,
• Dieter Lentz and
• Hans-Ulrich Reissig

Beilstein J. Org. Chem. 2012, 8, 662–674, doi:10.3762/bjoc.8.74

• quaternary carbon atoms in the 13C NMR spectrum evidenced the presence of the pyrrole structure. Finally, the HMBC experiment proved the proposed substitution pattern at the pyrrole ring. HRMS and elemental analysis allowed identification of 5 as a 2,3,4,5-tetrasubstituted pyrrole derivative. As shown in

Marilones A–C, phthalides from the sponge-derived fungus Stachylidium sp.

• Celso Almeida,
• Stefan Kehraus,
• Miguel Prudêncio and
• Gabriele M. König

Beilstein J. Org. Chem. 2011, 7, 1636–1642, doi:10.3762/bjoc.7.192

• correlations from 9’-H3 to C-2’, C-3’ and C-4’, and from methyl protons 8’-H3 and 10’-H3 to C-6’and C-7’, disclosing a geranyl fragment. Based on literature comparisons we established the configuration of Δ2’/3’ as E [11]. The aromatic quaternary carbon C-5 (δC 164.2) had a carbon resonance that indicated a

Translation of microwave methodology to continuous flow for the efficient synthesis of diaryl ethers via a base-mediated S_NAr reaction

• Charlotte Wiles and
• Paul Watts

Beilstein J. Org. Chem. 2011, 7, 1360–1371, doi:10.3762/bjoc.7.160

• spectra 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

One-pot Diels–Alder cycloaddition/gold(I)-catalyzed 6-endo-dig cyclization for the synthesis of the complex bicyclo[3.3.1]alkenone framework

• Boubacar Sow,
• Gabriel Bellavance,
• Francis Barabé and
• Louis Barriault

Beilstein J. Org. Chem. 2011, 7, 1007–1013, doi:10.3762/bjoc.7.114

• Boubacar Sow Gabriel Bellavance Francis Barabe Louis Barriault Department of Chemistry, 10 Marie Curie, University of Ottawa, Ottawa, Canada, K1N 6N5 10.3762/bjoc.7.114 Abstract The rapid synthesis of bicyclo[m.n.1]alkanone cores possessing quaternary carbon centers adjacent to a bridged ketone

When gold can do what iodine cannot do: A critical comparison

• Sara Hummel and
• Stefan F. Kirsch

Beilstein J. Org. Chem. 2011, 7, 847–859, doi:10.3762/bjoc.7.97

• stereocenters, including a quaternary carbon. As in the previous examples, the gold-catalyzed cyclization benefits strongly from a stabilizing substituent at C2 to direct the 6-endo mode of cyclization. Subsequent to the success of the gold-catalyzed cycloisomerization in trapping the developing carbocation

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