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Aqueous Asymmetric Mukaiyama Aldol Reaction Catalyzed by Chiral Gallium Lewis Acid with Trost‐Type Semi‐Crown Ligands
Author(s) -
Li HuiJing,
Tian HongYu,
Wu YanChao,
Chen YongJun,
Liu Li,
Wang Dong,
Li ChaoJun
Publication year - 2005
Publication title -
advanced synthesis and catalysis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.541
H-Index - 155
eISSN - 1615-4169
pISSN - 1615-4150
DOI - 10.1002/adsc.200505089
Subject(s) - chemistry , aldol reaction , enol , lewis acids and bases , silylation , silyl enol ether , organic chemistry , acetal , lewis acid catalysis , catalysis , enol ether , benzaldehyde , substituent , enantioselective synthesis , medicinal chemistry
Abstract The combination of Ga(OTf) 3 with chiral semi‐crown ligands ( 1a – e ) generates highly effective chiral gallium Lewis acid catalysts for aqueous asymmetric aldol reactions of aromatic silyl enol ethers with aldehydes. A ligand‐acceleration effect was observed. Water is essential for obtaining high diastereoselectivity and enantioselectivity. The p ‐phenyl substituent in aromatic silyl enol ether ( 2 h ) plays an important role and increases the enantioselectivity up to 95% ee. Although aliphatic silyl enol ethers provided low enantioselectivities and silylketene acetal is easily hydrolyzed in aqueous alcohol, the aldol reactions of silylketene thioacetal ( 12 ) with aldehydes in the presence of gallium‐Lewis acid catalysts give the β‐hydroxy thioester with reasonable yields and high diastereo‐ (up to 99 : 1) and enantioselectivities (up to 96% ee).