Li a-(dimethylamino)alkoxides resulting from the nucleophilic addn. of an organolithium reagent to DMF are basic enough to deprotonate alkyltriphenylphosphonium salts suspended in THF. The aldehydes, liberated by the spontaneous decompn. of the resulting a-amino alcs. (hemi-aminals), undergo a Wittig reaction with the simultaneously generated P ylides to afford olefins in excellent overall yields. This in situ method offers the unique advantage in its applicability to labile aldehydes which otherwise would become prey to (Z/E)-isomerization or self-condensation processes. [on SciFinder (R)]