Phosphorylide complexes, Li+[Ph3P+C-HR]X-, where R = H, alkyl, or alkoxy, gives very poor yields of olefins from aldehydes in the Wittig reaction. In the presence of 1.1 equivs. tert-BuOK the reaction is strongly accelerated. By this method methylenecyclohexane, styrene, w-methylstyrene, w,w-dimethylstyrene, 4-octene, 1-phenyl-1-hexene, and 1,1-diphenylethylene, resp., are prepd. in 60-91% yields by treating cyclohexanone, BzH, BzH, BzH, butyraldehyde, BzH, and BzPh, resp., at 22 Deg 0.5-15.0 h. It is postulated that the intermediate [Ph2P+CHRCH(O-Li+)R']X- reacts to give the K+ deriv., which dissocs. more easily to Ph3P+CHRCHO-R', necessary for the formation of I, which gives RCH:CHR' and Ph3PO. [on SciFinder (R)]