S-, P-stabilized bromoallenes for modular allenylborylation of alkenes

Simultaneously forming a carbon-carbon and a carbon-heteroatom bond in a single step through transition metal-catalyzed alkene difunctionalization strategy has emerged as a powerful tool for synthetic organic chemistry. Due to the uncontrollable reactivity, direct cross-coupling with bromoallenes as the building blocks for the selective allenation and borylation remains challenging. We herein report a new type of S- and P-stabilized bromoallenes for palladium-catalyzed modular allenation and borylation of alkenes to the divergent synthesis of multiply functionalized allenes in a highly regio- and diastereoselective manifold. The reaction features broad substrate scope and wide functional group compatibility, thus providing a straightforward method to install allenyl and boryl groups across alkenes. Control experiments highlight the crucial importance of S-, P-stabilization for the oxidative insertion of Pd-species into the allenyl-Br bond. The facile syntheses of bioactive allenic steroids and exocyclic allenes demonstrate the synthetic utility of this protocol.