Copper-Catalysed Asymmetric Conjugate Addition of Organometallic Reagents to Linear Enones
作者:Simon M.W Bennett、Stephen M Brown、Anthony Cunningham、Michael R Dennis、James P Muxworthy、Michael A Oakley、Simon Woodward
DOI:10.1016/s0040-4020(00)00140-x
日期:2000.4
Methods for enantioselective 1,4-addition of main-group organometallics to linearenones are overviewed. Thiourethane and thioether 1,1′-binaphthyl-based ligands are effective for copper-catalysed 1,4-addition of ZnEt2 and AlR3 (R=Me, Et) to trans-alkyl-3-en-2-ones; enantioselectivities of up to 72% e.e. are attained. In comparison 1,4-addition of ZnEt2 to 2-cyclohexenone proceeds in up to 77% e.e
A kinetic analysis of the asymmetric addition of trimethylsilyl cyanide to benzaldehyde using three aluminium based catalysts has been carried out. All three catalysts displayed rate equations, which were first order in trimethylsilyl cyanide concentration and zero order in benzaldehyde concentration. The results are consistent with a common mechanism for effective asymmetric catalysis of cyanohydrin synthesis, involving combined activation of the aldehyde by a Lewis acid and activation of the trimethylsilyl cyanide by a Lewis base. The mechanistic analysis was also applied to a magnesium-based catalyst system to demonstrate its general applicability. (C) 2010 Elsevier Ltd. All rights reserved.
A new methodology for the stereoselective synthesis of 4-substituted butenolides: Asymmetric Michael addition reaction of 2-(trimethylsilyloxy)furans to oxazolidinone enoates
作者:Hiroshi Kitajima、Katsuji Ito、Tsutomu Katsuki
DOI:10.1016/s0040-4020(97)10152-1
日期:1997.12
Chiral Lewis acid promoted Michael addition of 2-(trimethylsilyloxy)furans to oxazolidinone enoates (2) in the presence of hexafluoroisopropanol proceeded stereoselectively to give 4-substituted butenolides in good yields. A 1:1 complex prepared in situ from Sc(OTf)(3) and 3,3'-bis(diethylaminomethyl)-1,1'-bi-2-naphthol 5b showed excellent anti-selectivity and moderate enantioselectivity, while Cu(OTf)(2)-bis(oxazoline) complex exhibited excellent enantioselectivity and moderate to good anti-selectivity. (C) 1997 Elsevier Science Ltd.