Alkylation and aldol reactions of acyl derivatives of N-1-(1′-naphthyl)ethyl-O-tert-butylhydroxylamine: asymmetric synthesis of α-alkoxy-, α-substituted-β-alkoxy- and α,β-dialkoxyaldehydes
摘要:
Treatment of a range of O-protected glycolate derivatives of the chiral auxiliary N-1-(1'-naphthyl)ethyl-O-tert-butylhydroxylamine with KHMDS in the presence of 18-crown-6 followed by addition of an alkyl halide generates alpha-substituted derivatives with very high levels of diastereoselectivity. Alternatively, reaction of the potassium enolate of a propanoate or O-protected glycolate derivative of N-1-(1'-naphthyl)ethyl-O-tert-butylhydroxylamine with a range of aldehydes gives syn-aldol products with high levels of diastereoselectivity. These adducts may be reductively cleaved with LiAlH(4) to give enantiopure alpha-alkoxy-, alpha-substituted-beta-alkoxy- and alpha,beta-dialkoxyaldehydes in good yield. (C) 2010 Elsevier Ltd. All rights reserved.
The Chiral Auxiliary <i>N</i>-1-(1′-Naphthyl)ethyl-<i>O</i>-<i>tert</i>-butylhydroxylamine: A Chiral Weinreb Amide Equivalent
作者:Alexander N. Chernega、Stephen G. Davies、Christopher J. Goodwin、David Hepworth、Wataru Kurosawa、Paul M. Roberts、James E. Thomson
DOI:10.1021/ol901174t
日期:2009.8.6
The chiral auxiliary N-1-(1'-naphthyl)ethyl-O-tert-butylhydroxylamine is readily prepared from N-hydroxyphthalimide in four steps, with resolution giving access to both enantiomers in >98% ee, on a multigram (>25 g) scale. Conversion to a range of N-acyl derivatives, followed by highly diastereoselective alkylation (>= 94% de) gives the corresponding chiral, 2-substituted derivatives as single diastereoisomers (>98% de) after chromatography. Reductive cleavage with LlAlH(4) allows direct access to chiral aldehydes, and treatment with MeLi gives chiral methyl ketones in excellent enantiopurity (>= 94% ee). The auxiliary can be recovered in >98% ee and recycled.
Alkylation and aldol reactions of acyl derivatives of N-1-(1′-naphthyl)ethyl-O-tert-butylhydroxylamine: asymmetric synthesis of α-alkoxy-, α-substituted-β-alkoxy- and α,β-dialkoxyaldehydes
作者:Alexander N. Chernega、Stephen G. Davies、Ai M. Fletcher、Christopher J. Goodwin、David Hepworth、R. Shyam Prasad、Paul M. Roberts、Edward D. Savory、Andrew D. Smith、James E. Thomson
DOI:10.1016/j.tet.2010.03.105
日期:2010.6
Treatment of a range of O-protected glycolate derivatives of the chiral auxiliary N-1-(1'-naphthyl)ethyl-O-tert-butylhydroxylamine with KHMDS in the presence of 18-crown-6 followed by addition of an alkyl halide generates alpha-substituted derivatives with very high levels of diastereoselectivity. Alternatively, reaction of the potassium enolate of a propanoate or O-protected glycolate derivative of N-1-(1'-naphthyl)ethyl-O-tert-butylhydroxylamine with a range of aldehydes gives syn-aldol products with high levels of diastereoselectivity. These adducts may be reductively cleaved with LiAlH(4) to give enantiopure alpha-alkoxy-, alpha-substituted-beta-alkoxy- and alpha,beta-dialkoxyaldehydes in good yield. (C) 2010 Elsevier Ltd. All rights reserved.