. . . . "Suitable ylids include those having the formula: ##STR4## wherein X and Y are H, alkyl, aryl, halogen, carbonyl, CO.sub.2--R, OR, NH.sub.2, SR where R=hydrogen, alkyl, aryl, acetyl; and L is a leaving group capable of being expelled upon migration of the alkyl group from the organoborane to the ylid during the homologation reaction." . .