Using amide conformation to ‘project’ the stereochemistry of an (−)-ephedrine-derived oxazolidine: a pair of pseudoenantiomeric chiral amido-phosphine ligands
作者:Jonathan Clayden、Lai Wah Lai、Madeleine Helliwell
DOI:10.1016/s0957-4166(01)00110-0
日期:2001.4
Protection of a tertiary 2-formylbenzamide as an (-)-ephedrine-derived oxazolidine both Fords the amide's stereogenic Ar-CO axis to adopt one of two possible diastereoisomeric conformations and protects the formyl group from attack during amide ortho-lithiation. By functionalising the amide in the 6-position, reactive sites (such as -CHO, -SR, -PR2 groups) may be introduced which fall under the stereochemical influence, relayed by the amide: of the (-)-ephedrine-derived oxazolidine. This 'projection' of stereochemistry is exemplified by a pair of amido-phosphines. members of the first ever class of non-biaryl atropisomeric ligands, which are made functionally pseudoenantiomeric by the intervention of either one or two amide groups between the (-)-ephedrine-derived oxazolidine and the PPh2 group. The pseudoenantiomeric amido-phosphines promote the palladium-catalysed asymmetric allylation of dimethyl malonate in 82 and -53% e.e., respectively. (C) 2001 Published by Elsevier Science Ltd.