Auto-tandem palladium/phosphine cooperative catalysis: synthesis of bicyclo[3.1.0]hexenes by selective activation of Morita-Baylis-Hillman carbonates

Herein we report a new palladium/phosphine cooperative catalytic system for the synthesis of bicyclo[3.1.0]hexene derivatives, particularly useful structural motifs in numerous biologically active entities. By application of our palladium/phosphine cooperative catalytic system, we accomplish the first selective intermolecular activation of Morita-Baylis-Hillman carbonates, where the phosphine species leads to a zwitterionic allylic ylide and the Pd catalyst generates a pi-allylpalladium complex. Experimental results indicate that both the Pd and phosphine play crucial roles in the sequential annulation reaction. This strategy opens up a new avenue for efficient and economical metal/Lewis base dual catalytic systems and provides valuable clues on solving the limitations of selective activation.