An improved asymmetric nitroolefination of α-alkyl-γ- and δ-lactones with modified nitroenamines
摘要:
New chiral nitroenamines 4a, b were found to be very effective for asymmetric nitroolefination of alpha-alkyl-gamma- and delta-lactones. The enantiomeric excess of the product ran up to 99%. A possible chelation model for the transition state of the asymmetric nitroolefination was discussed.
An efficient asymmetric synthesis of nitroolefinic lactones with chiral nitroenamines possessing bulky chiral leaving groups
作者:Xiaowu Yang、Rui Wang
DOI:10.1016/s0957-4166(97)00452-7
日期:1997.10
An efficient asymmetric nitroolefination of enolates 4a-c, 5 afforded multifunctional group nitroolefinic lactones 7a-e and 8a,b containing stereogenic quaternary carbon centers using bulky chiral nitroenamines 1a,b–3a,b as chiral auxiliaries. Studies on the effect of the bulkiness of leavinggroup showed that bulky nitroenamines 1a,b gave higher ees and yields than those of the less bulky 2a,b–3a
New chiral nitroenamines 4a,b having (S)-2-t-butyldimethylsiloxymethylpyrrolidine as an auxiliary were found to be very effective for asymmetric nitroolefination of alpha-alkyl-gamma- and delta-lactones. The enantiomeric excess of the product increased remarkably in the reaction with gamma-lactones compared with previous nitroenamines 1a,b. A possible chelation model for the transition state of the asymmetric nitroolefination is discussed.
On the reactivity of some 2-methyleneindolines with β-nitroenamines, α-nitroalkenes, and 1,2-diaza-1,3-butadienes
A study of the behaviour of some electron-rich 2-methyleneindolines (1-3) with different electron-poor reagents (formation of new carbon-carbon and nitrogen-carbon bonds) has furnished interesting results from both synthetic and the mechanistic viewpoints. Enamines 1-3 have been reacted with the beta-nitroenamines 4-7 (reaction CeCl3 center dot 7H(2)O promoted), giving the polymethine dyes 14-23. The same bases 1-3 have been nitroalkylated with the nitroolefins 8-10, furnishing the indolines 24-32, and the diastereoselectivity of the reaction has been thoroughly investigated. The most unexpected results derived from the first example of reaction of Fischer's bases with 1,2-diaza-1,3-butadienes. In fact, with 11-13, the 'unknown' indoline spirodihydropyrroles 33-40 were formed. Their structures were unambiguously assigned, and we determined, as an example, that of 33 by X-ray analysis. (c) 2006 Elsevier Ltd. All rights reserved.
Direct asymmetric synthesis of quaternary carbon centers by the addition-elimination process: nitroolefination of .alpha.-substituted .delta.-lactones