Accelerated transmetallation in Stille couplings effected by chelation to the palladium

The relative reactivities of vinylstannanes 2a,b and 4a,b in a Stille coupling with vinyl bromide were studied under a variety of conditions. Vinyl bromide coupled with the sterically hindered vinylstannane 2a preferentially compared to the less hindered stannane 2b when PdCl₂(CH₃CN)₂ was employed as a catalyst. Coordination of the nitrogen of the imine protecting group to the palladium is proposed to account for this rate acceleration.Geoffrey T. Crisp, Markus G. Gebaue