THF Solvent as a Proton Shuttle in the AuCl3-Catalyzed Cycloisomerization of a Bromoallenyl Ketone: A Mechanistic DFT Study

The solvent effect on the regiochemistry of the AuCl3-catalyzed cycloisomerization of a bromoallenyl ketone was evaluated by DFT calculations, which provided theoretical rationale for the original experimental findings from the Gevorgyan group. Upon the generation of the gold carbenoid intermediate from cyclization of the allene precursor, the tetrahydrofuran solvent could act as a proton shuttle to assist the 1,2-H migration to afford the 2-bromofuran product. This solvent-involved pathway is lower in energy than the 1,2-Br migration and thus leads to a solvent-controlled switch of regioselectivity in the reaction concerned.