α,β-Disubstituted allylzincs with alkoxycarbonyl as the β-substituent, generated via an umpolung of in situ generated π-allylpalladium by transmetallation with diethylzinc, react with benzaldehyde at the most substituted allylic terminus to provide syn-γ-butyrolactones 4 exclusively, while those with electron-donating Me, i-Pr, or OMOM as the β-substituents react at both allylic termini to give mixtures of syn-2, anti-2 and Z-3. α,β,γ-Trisubstituted allylzincs provide Z,anti-adducts 5 exclusively.