Using amide conformation to 'project' the stereochemistry of an (-)-ephedrine-derived oxazolidine: A pair of pseudoenantiomeric chiral amido-phosphine ligands

Protection of a tertiary 2-formylbenzamide as an (-)-ephedrine-derived oxazolidine both forces 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.