Highly regioselective synthesis of trisubstituted allenes via lithiation of 1-aryl-3-alkylpropadiene, subsequent transmetalation, and Pd-catalyzed Negishi coupling reaction.

A novel methodology for the synthesis of trisubstituted allenes is reported. Lithiation of 1-aryl-3-alkylpropadienes and subsequent transmetalation with zinc bromide followed by Pd-catalyzed Negishi coupling reactions with halides afforded the corresponding trisubstituted allenes in a highly regioselective fashion with moderate to excellent yields. A plausible regioselective lithiation mechanism was proposed on the basis of deuterium labeling experiments.