Molybdenum-Catalyzed Cross-Coupling of Benzyl Alcohols: Direct C-OH Bond Transformation via [2 + 2]-Type Addition and Elimination.

Traditional cross-couplings catalyzed by transition metal catalysts generally rely on the classic oxidative addition-transmetalation-reductive elimination process, which requires low-valent precious metals and an inert atmosphere and which initiates from carbon-alide or pesudo carbon-halide bonds. Herein, an unprecedented molybdenum-oxo-complex-catalyzed intermolecular cross-coupling of benzyl alcohols has been reported. Various alcohols including primary, secondary, and tertiary substrates can proceed efficiently under these conditions. Several functional groups sensitive to the low-valent transition metals, such as aryl halides, can be well tolerated. The mechanistic studies and DFT calculations suggest that an intramolecular concerted cyclization was involved in the reverse [2 + 2]-type elimination process.