Rapid Formation of Fluoren-9-ones via Palladium-Catalyzed External Carbon Monoxide-Free Carbonylation

A Pd-catalyzed carbonylation reaction for the synthesis of fluoren-9-ones from 2-halogenated biphenyls using phenyl formate as a carbon monoxide surrogate was achieved. The combined use of cesium carbonate and o-anisic acid resulted in a remarkable rate enhancement, where the reaction was complete within 3 min in some cases. Mechanistic studies indicated that the turnover-limiting step of the reaction was the C-H bond-cleaving step or the oxidative addition step, depending on the substrate used.