Reaction of Ph3P+C-HR with R1CHO at -78 Deg yielded Ph3P+CHRCHR1O- (I). Subsequent addn. of BuLi gave Ph3P+C-RCHR1O- Li+ (II). Reaction of II with HCl and hydrolysis with tert-BuOK gave .apprx.80% RCH:CHR1 (R = Et, Ph, or C5H11; R1 = Me, Et, or C5H11). When the reaction was performed in the presence of LiClO4, nearly pure trans isomer was obtained, while in the absence of Li salts reaction was not stereoselective, indicating that Li salts favored the threo form of I. Na salts had a similar effect. [on SciFinder (R)]