Mechanistic Investigation of Rh^I–Catalyzed Cycloisomerization of Benzylallene-Internal Alkynes via C–H Activation

Treatment of the benzylallene-internal alkynes with [RhCl­(CO)2]2 effected a cycloisomerization via a Csp2–H bond activation to produce the tricyclo­[9.4.0.03,8]­pentadecapentaene skeleton. The reaction mechanism via formation of the rhodabicyclo[4.3.0] intermediates and σ-bond metathesis between the Csp2–H bond on the benzene ring and the Csp2–RhIII bond was proposed. In addition, a plausible alternative mechanism for the previously reported cycloisomerization of the benzylallene-terminal alkynes could also be proposed.