Palladium-Catalyzed Preparation of Vinylallenes from 2-Bromo-1,3,5-trienes via an Alkylidene-π-allylpalladium-Mediated Formal S_N2‘ ‘ Pathway

Abstract

[Structure: see text] A novel Pd-catalyzed reaction to prepare conjugated vinylallenes from 2-bromo-1,3,5-triene and a soft nucleophile via a formal SN2" pathway was developed. The reaction proceeds via alkylidene-pi-allylpalladium and allenyl-pi-allylpalladium intermediates, and a dynamic process involving the two palladium intermediates played important roles in determining the selectivity of the Pd-catalyzed reaction. The reaction was extended to an asymmetric counterpart, and an axially chiral vinylallene was obtained with up to 81% ee.