Stereoselective functionalisation of SuperQuat enamides:: asymmetric synthesis of homochiral 1,2-diols and α-benzyloxy carbonyl compounds

Homochiral (E)- and (Z)-enamides derived from SuperQuat (S)-4-phenyl-5,5-dimethyl-oxazolidin-2-one Undergo highly diastereoselective epoxidation upon treatment with dimethyldioxirane. Subsequent epoxide opening will) meta-chlorobenzoic acid proceeds via a stereoselective S(N)1-type process, with retention of Configuration, to give the corresponding 1'-m-chlorobenzoly-2'-hydroxy derivatives. Treatment of the SuperQuat enamides with mCPBA effects this two-step transformation in one pot. Reductive cleavage of the isolated 1'm-chlorobenzoly-2'-hydroxy derivatives (>= 96% de) generates homochiral 1,2-diols in > 96% ee. Alternatively. regioselective lithiation of the enamide at Q F) with 'BuLi followed by reaction with an aromatic aldehyde and in Situ O-benzylation generates a 1'-(benzyloxyaryl-methyl) substituted enamide with high diastereoselectivity. Subsequent oxidative cleavage of the enamide C-C bond with NalO(4)/RuCl3 followed by methanolysis of the resultant N-acyl fragment furnishes all O-benzyl protected g-hydroxy methyl ester in high ee. (C) 2008 Elsevier Ltd. All rights reserved.