Highly Diastereoselective Conjugate Addition of Lithium Dialkylamides to α,β-Unsaturated Esters Having a Chiral Center at the γ-Position
摘要:
The conjugate addition of lithium amides 2 to tert-butyl 4-(OR)-substituted-2-pentenoates 1 produced a mixture of the syn-and anti-amino esters (3 and 4) in high yields. Sterically bulky OR groups, such as trityloxy and tert-butyldiphenylsilyloxy, gave the syn diastereomer 3 either exclusively or predominantly. The syn-selectivity may be explained by a modified Felkin-Anh model. The use of tert-butyldimethylsilyloxy as an OR group afforded a nearly 1:1 mixture of diastereoisomers, and the use of the smallest MeO group produced a 63:37 mixture of the syn 3 and anti isomer 4. The presence of Me group at the alpha-position (C-2 position) of the enoate enhanced the syn diastereoselectivity up to 100%; the conjugate addition to tert-butyl 4-methoxy-2-methyl-2-pentenoate (17) gave the syn-isomer 18 exclusively. This enhancement may be explained by the combination of chelation and allylic strain model 19 in which the smallest H orients inside to avoid an allylic strain. A phenyl group at the gamma-position enhanced the anti selectivity in the case of gamma-alkoxy-alpha,beta-enoates such as isopropyl 4-[(tert-butyldimethylsilyl)oxy]-4-phenyl-2-buteonoate (20), and in the case of gamma-alkyl-alpha,beta-enoates such as tert-butyl 4-phenyl-2-pentenoate (27).
Highly Diastereoselective Conjugate Addition of Lithium Dialkylamides to α,β-Unsaturated Esters Having a Chiral Center at the γ-Position
摘要:
The conjugate addition of lithium amides 2 to tert-butyl 4-(OR)-substituted-2-pentenoates 1 produced a mixture of the syn-and anti-amino esters (3 and 4) in high yields. Sterically bulky OR groups, such as trityloxy and tert-butyldiphenylsilyloxy, gave the syn diastereomer 3 either exclusively or predominantly. The syn-selectivity may be explained by a modified Felkin-Anh model. The use of tert-butyldimethylsilyloxy as an OR group afforded a nearly 1:1 mixture of diastereoisomers, and the use of the smallest MeO group produced a 63:37 mixture of the syn 3 and anti isomer 4. The presence of Me group at the alpha-position (C-2 position) of the enoate enhanced the syn diastereoselectivity up to 100%; the conjugate addition to tert-butyl 4-methoxy-2-methyl-2-pentenoate (17) gave the syn-isomer 18 exclusively. This enhancement may be explained by the combination of chelation and allylic strain model 19 in which the smallest H orients inside to avoid an allylic strain. A phenyl group at the gamma-position enhanced the anti selectivity in the case of gamma-alkoxy-alpha,beta-enoates such as isopropyl 4-[(tert-butyldimethylsilyl)oxy]-4-phenyl-2-buteonoate (20), and in the case of gamma-alkyl-alpha,beta-enoates such as tert-butyl 4-phenyl-2-pentenoate (27).
Acyclic stereoselection. 40. Steric effects, as well as .sigma.*-orbital energies, are important in diastereoface differentiation in additions to chiral aldehydes
作者:Eric P. Lodge、Clayton H. Heathcock
DOI:10.1021/ja00245a027
日期:1987.5
Etude desreactions d'aldolisation de deux series d'aldehydes chiraux avec l'enolate de lithium de la pinacolone
练习曲 d'aldolisation de deux series d'aldehydes chiraux avec l'enolate delithium de la pinacolone
Preparation of 2-methoxy-1-alkanols and 2-methoxy-1-alkanals
申请人:DU PONT
公开号:US02555950A1
公开(公告)日:1951-06-05
Boche, Gernot; Bosold, Ferdinand; Lohrenz, John C. W., Chemische Berichte, 1993, vol. 126, # 8, p. 1873 - 1886
作者:Boche, Gernot、Bosold, Ferdinand、Lohrenz, John C. W.、Opel, Achim、Zulauf, Peter
DOI:——
日期:——
Factors affecting the regioselectivity in the rhodium-catalysed hydroformylation of vinyl ethers