POLYFUNCTIONALIZED PYRROLIDINES BY STEREOSELECTIVE 1,3-DIPOLAR CYCLOADDITION OF AZOMETHINE YLIDES TO CHIRAL ENONES

The cycloaddition reactions of chiral alpha,beta-unsaturated ketones substituted by alkoxy or amino groups in the gamma-position to azomethine ylides (obtained from glycine imines) were investigated in the presence of a base, LiBr and AgOAc. High regioselectivities were observed in most cases, resulting in the formation of a single diastereomer, particularly if a DBU/AgOAc catalyst system was employed. The influence of reaction conditions and olefin structure on the stereoselectivity of the reaction was investigated, and models rationalizing stereocontrol are proposed. In addition, an interesting deconjugation reaction of acetals derived from gamma,delta-dihydroxy alpha,beta-unsaturated enones or esters is described.