- A flexible approach to azasugars: asymmetric total syntheses of (+)-castanospermine, (+)-7-deoxy-6-epi-castanospermine, and (+)-1-epi- castanospermine
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The asymmetric total synthesis of natural azasugars (+)-castanospermine, (+)-7-deoxy-6-epI-castanospermine, and synthetic (+)-1-epi-castanospermine has been accomplished in nine to ten steps from a common chiral building block (S)-8. The method features a powerful chiral relay strategy consisting of a highly diastereoselective vinylogous Mukaiyama-type reaction with either chiral or achiral aldehydes (≥ 95% de; de = diastereomeric excess) and a diastereodivergent reduction of tetramic acids, which allows formation of three continuous stereogenic centers with high diastereo-selectivities. The method also provides a flexible access to structural arrays of 5-(α-hydroxyalkyl) tetramic acids, such as 17/34, and 5-(α-hydroxyalkyl)-4-hydroxyl-2- pyrrolidinones, such as 18 and 25/35 a. The method constitutes the first realization of the challenging chiral synthons A and D and thus of the conceptually attractive retrosynthetic analysis shown in Scheme 1 in a highly enantioselective manner.
- Liu, Gang,Wu, Tian-Jun,Ruan, Yuan-Ping,Huang, Pei-Qiang
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supporting information; experimental part
p. 5755 - 5768
(2010/08/19)
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- New and concise approach to (R)-α-lipoic acid
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A concise enantiospecific synthesis of (S)-6,8-bis(methylsulfonyloxy)- octanoic acid (2), a ready precursor of (R)-(+)-α-lipoic acid (1), is reported. The key step of the synthesis is the coupling of the tosylate derived from (R)-malic acid with phenylpro
- Wei, Zhen,Lan, Hong-Qiao,Zheng, Jian-Feng,Huang, Pei-Qiang
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experimental part
p. 691 - 701
(2009/07/18)
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- Stereoselection in radical cyclization of β-alkoxyvinyl sulfoxides: Synthesis of tetrahydrofuranyl allyl carbinols
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Equation presented. Tetrahydrofuranyl allyl carbinols may be prepared stereoselectively via radical cyclization of β-alkoxyvinyl sulfoxides, Pummerer rearrangement, and reaction with allylstannane.
- Keum, Gyochang,Kang, Soon Bang,Kim, Youseung,Lee, Eun
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p. 1895 - 1897
(2007/10/03)
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- Towards the diastereoselective functionalization of non-racemic acetal derivatives of η6-arylcarbonyl complexes of tricarbonylchromium
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(S)-Butane-1,2,4-triol (2) has been investigated as a potential chiral auxiliary for the formation of non-racemic acetals derived from η6-arylcarbonyl complexes of tricarbonylchromium. Predominantly the cis dioxan (5) was formed from benzaldehyde, leading to preparation of the η6-Cr(CO)3 complex (16), and of the derived complexes (23) and (24). Lithiation-electrophile quenching of these complexes gave a mixture of products arising from ortho and benzylic functionalization. Reaction of acetophenone, or of the η6-Cr(CO)3 complexes (45) or (46), with either the triol (2) or its tris(silyl) ether (15) under conditions of kinetic or thermodynamic control gave an inseparable mixture of acetals.
- Kendall, Jackie D.,Woodgate, Paul D.
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p. 1083 - 1096
(2007/10/03)
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- An enantiocontrolled synthesis of pyrrolizidines, (-)-platynecine and (-)-hadinecine
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Trisubstituted allylic alcohols 13 and 14 have been converted into a single isomeric trans-oxazoline 16 via an intramolecular iodoamidation of the corresponding trichloroacetimidates, which have been elaborated into (-)-platynecine 1 and(-)-hadinecine 2 via a common intermediate pyrrolizidine.
- Kang, Sung Ho,Kim, Geun Tae,Yoo, Yong Sang
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p. 603 - 606
(2007/10/03)
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- Stereoselective syntheses and reactions of chiral oxygenated α,β-unsaturated-γ- and δ-lactones
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The syntheses of the chiral α,β-unsaturated lactones (+)-5, (-)-6, (+)-8, (+)-9, and (+)-10 have been efficiently achieved from readily available starting materials. The lactone (+)-5 has been synthesized in 7 steps from (R,R)-dimethyl tartrate (38-43% overall yield). The use of (+)-5 in formal syntheses of natural (+)-asperlin 4 and advanced intermediates for (+)-olguine 2 are also reported. The lactone (-)-6 has been prepared in 5 steps from (R)-malic and (44-50% overall yield). It can be a useful precursor for the syntheses of branched chain and deoxy nucleoside analogues. The preparation of (-)-6 constitutes formal syntheses of natural (+)-eldanolide 53 and the (+)-Geissman-Waiss lactone 54 (an intermediate for the syntheses of a variety of pyrrolizidine alkaloids). The lactones (+)-8, (+)-9 and (+)-10 have been synthesized from 3,4-di-O-acetyl-L-rhamnal 58. The highly diastereoselective transformations of (+)-9 and (+)-10, through sequential conjugate nucleophilic addition and enolate reaction, into densely functionalized chiral γ-lactones 12 are also reported. Copyright (C) Elsevier Science Ltd.
- Sanchez-Sancho, Francisco,Valverde, Serafin,Herradon, Bernardo
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p. 3209 - 3246
(2007/10/03)
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