Bifunctional Biphenyl-2-ylphosphine Ligand Enables Tandem Gold-Catalyzed Propargylation of Aldehyde and Unexpected Cycloisomerization

Despite extensive studies in gold
catalysis, σ-allenylgold
species have not been invoked as catalytic intermediates and their
reactivities not studied. This work reports for the first time they
are generated in situ and undergo nucleophilic addition to activated
aldehydes in a bifunctional phosphine ligand-enabled gold catalysis.
This development reveals a broad range of opportunities to achieve
propargylic C–H functionalization for the first time under
catalytic and mild conditions. The homopropargylic alcohols generated
undergo ligand-enabled cycloisomerizations involving an unexpected
silyl migration.