Enantioselective Synthesis of α-Arylated Allene Ketones Through Sequential Bismuth(V)-mediated Arylation and Organocatalytic Protonation.

Triarylbismuth(V)-mediated arylation represents an important approach for synthesizing a wide range of α-arylated ketones and enol derivatives. Since the seminal work by Barton and colleagues in the 1980s, these C─C bond-forming transformations have been extensively explored. Despite significant progress, asymmetric variants of these reactions have yet to be developed. In this study, we document a sequential reaction consisting of bismuth-mediated α-arylation of allene ketones and an enantioselective protonation of α-arylated alkynyl ketones, leveraging the isomerization between allenyl and alkynyl intermediates. Our approach relies on a reversible/irreversible isomerization sequence comprising three distinct stages. The process initiates with the generation of enolates through reversible isomerization, followed by oxidative arylation and a subsequent enantioselective, irreversible isomerization to yield α-arylated allenones. Both experimental results and theoretical studies support our mechanistic proposal. The sequential bismuth(V)-mediated arylation and enantioselective proton transfer is conceptually significant, as coupling bismuth chemistry with asymmetric catalysis may open new avenues for organobismuth(V) chemistry in enantioselective transformations and extend its utility in synthetic organic chemistry.