LITHIUM DERIVATIVES FROM ENANTIOMERICALLY PURE 2-(2'-HALOETHYL) DIOXOLANES - FORMATION AND USE AS CHIRAL PROPANAL HOMOENOLATE SYNTHONS

Condensation of acetals of 3-chloro- and 3-bromopropanal with (-)-1,4- di-O-benzyI-L-threitol and (-)cis-2,3-bomanediol leads to the correspo nding 2-(2'-chloroethyl-)- and 2-(2'-bromoethyl)dioxolanes that were c onverted into the Li-derivatives by transhalometallation with t-butyll ithium in excellent yields. These chiral propanal homoenolates react w ith benzaldehyde and acetophenone yielding carbinols in moderate chemi cal yields and low diastereomeric excesses.