ENANTIOSELECTIVE CONJUGATE ADDITIONS OF SILYLKETENE ACETALS TO 2-CARBOXYCYCLOPENTENONES PROMOTED BY CHIRAL TI COMPLEXES

The conjugate addition of silylketeneacetals to 2-carbalkoxycyclopente nones 1 promoted by TADDOL . TiCl2 complexes was studied. The reaction s are highly syn selective. The enantioselectivity depends on the size of the substrate ester group, with the methyl ester 1b being more ena ntioselective than the ethyl ester 1a. E.c. up to 47% are achieved. Th e absolute configuration of the major product was established by chemi cal correlation to the known (+)-isodchydroiridodiol. The reaction of representative doubly activated alkenes was studied: good results were obtained with cyclopentenones and gamma-butenolides. (C) 1997 Publish ed by Elsevier Science Ltd.