THE DIASTEREOSELECTIVE SYNTHESIS OF ESTER-FUNCTIONALIZED ALKENES THROUGH THE STEREOCONTROLLED CONJUGATE ADDITION (MICHAEL REACTION) OF PROCHIRAL ENOLATES TO CHIRAL ALPHA-METHYLENE BETA-LACTONES AND THERMAL DECARBOXYLATION OF THE RESULTING ALPHA-SUBST

摘要

The conjugate addition of ester and ketone enolates to alpha-methylene beta-lactones 1 and 2 proceeds with high stereocontrol of the newly formed chiral centers. The beta-lactones 3-8 with ester functionalities in the alpha-side chain were obtained in good yields from the addition of ester enolates, while the dispiro-beta-lactones 9-11 were formed in the addition of acetophenone and propiophenone enolates. The decarboxylation of the resulting ester-functionalized beta-lactones produced quantitatively the corresponding gamma,delta-unsaturated esters 12-17 with complete retention of the initial beta-lactone geometry. This unprecedented two-step sequence, i.e. Michael addition followed by decarboxylation, constitutes the first stereoselective synthesis of ester-functionalized, (E)-configurated alkenes, in which the synthetic potential of the alpha-methylene beta-lactones as allene equivalents is advantageously utilized. [References: 48]