Ruthenium(II)-Catalyzed Regioselective-Controlled Allenylation/Cyclization of Benzimides with Propargyl Alcohols

A ruthenium­(II)-catalyzed cyclization of benzimidates with substituted propargyl alcohols to provide 3,4-disubstituted 1-alkoxy isoquinolines in a highly selective manner via the C–H allenylation is described. The proposed reaction mechanism of the ruthenium­(II)-catalyzed cyclization reaction is strongly supported by the isolation of the key ruthenacycle intermediate, deuterium-labeling studies, and detailed DFT calculations including the transition states.