DIASTEREOSELECTIVITY IN THE PREPARATION OF BETA-SILYL ESTERS FROM ALPHA-BETA-UNSATURATED ESTERS AND AMIDES ATTACHED TO CHIRAL AUXILIARIES

The conjugate addition of the phenyldimethylsilyl-cuprate reagent to cinnamate and crotonate esters and amides 1 of various known chiral auxiliaries, a-e, is diastereoselective. The sense of the diastereoselectivity of silyl-cuprate addition to the esters 1b-d, 8 and 9 is different from established precedent based on carbon-cuprates, but is normal for silyl-cuprate addition to the amide 1a, the imides 1e and 21, and the oxazolidine 6. The chiral auxiliary e gives the best results of those tested. and the silicon-containing group can be removed from the chiral auxiliary using alkoxide ion in aprotic media, making available beta-silyl esters 27-29 of high enantiomeric excess, with recovery of the chiral auxiliary 30.