SuperQuat, (S)-4-benzyl-5,5-dimethyl-oxazolidin-2-one for the asymmetric synthesis of α-substituted-aldehydes
摘要:
Reduction of alpha -substituted-(S)-N-acyl-4-benzyl-5,5-dimethyl-oxazolidin-2-ones with DIBAL-H in CH2Cl2 affords alpha -substituted aldehydes with no loss of stereochemical integrity at their alpha -centre. (C) 2000 Elsevier Science Ltd. All rights reserved.
An easy access to enantio-enriched α-substituted aldehydes by carbolithiation of β-phenyl or β-silyl-α,β-ethylenic aldehydes, protected with the monolithioamide of a chiral diamine
作者:Nathalie Brémand、Pierre Mangeney、Jean F Normant
DOI:10.1016/s0040-4039(01)00034-x
日期:2001.3
Lithium amide derived from N,N,N'-trimethyl-l,2-diphenylethanediamine converts cinnamaldehyde to a lithium alkoxyamide which undergoes a regio- and stereoselective carbolithiation upon addition of various organolithiums. Subsequent hydrolysis or trapping with MeI delivers alpha -mono-, or alpha,beta -disubstituted 3-phenylpropanals with e.e.s of 76-96%. Extension to a silylated alpha -enal is possible. (C) 2001 Published by Elsevier Science Ltd.
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.