Asymmetric synthesis via norephedrine derived 2-alkenyloxazolidines

Abstract

The stereochemistry of the acid catalysed cyclization between N-protected norephedrine and α,β-unsaturated dimethyl acetals to give 2-alkenyloxazolidines is described. Such heterocycles, on the basis of their different formation and reactivity behaviour, are classified as electron rich or electron poor olefinic appendages. The mechanism and the factors determining the kinetic preference for the cis C-2/C-5 isomer is discussed. Experimental evidence together with theoretical considerations provide a reasonable rationalization for the observed selectivity of the conjugate addition. The addition of cuprates KC10, NaOCH 2 C 6 H 5, and (CH 3) 2 C=P(C 6 H 5) 3 to α,β-unsaturated esters, ketones and aldehydes with a chiral oxazolidine in γ position, occur with high stereoselectivity and yield. The corresponding adducts provide a useful tool for manipulation to more complex structures. © 1988 IUPAC