alpha,beta-Disubstituted allylzincs with alkoxycarbonyl as the beta-substituent, generated via an umpolung of in situ generated pi-allylpalladium by transmetallation with diethylzinc, react with benzaldehyde at the most substituted allylic terminus to provide syn-gamma-butyrolactones 4 exclusively, while those with electron-donating Me, i-Pr, or OMOM as the beta-substituents react at both allylic termini to give mixtures of syn-2, anti-2 and Z-3. alpha,beta,gamma-Trisubstituted allylzincs provide Z,anti-adducts 5 exclusively. (C) 1998 Elsevier Science Ltd. All rights reserved.