Cobalt-catalyzed ring expansion/ring opening of oxetanes using phosphine oxides as promoters under hydroformylation conditions

Abstract

Phosphine oxides, especially tricyclohexylphosphine oxide (P7), promote the cobalt catalyzed carbonylative ring expansion and reductive ring opening reaction of oxetanes under syngas atmosphere. Depending on the substrate structure and the stability of the carbocation intermediate either γ-lactones or primary alcohols are obtained in moderate to excellent yields. Syngas proved to play a crucial role for the catalyst activity and its stability in this process. Green solvents with high sustainability rankings, such as dimethyl carbonate (DMC), can be used in replacement of traditional solvents. The optimized conditions for both procedures were substrate (1 mmol), Co2(CO)8 (2 mol%), DMC (2 mL), 100 °C, gas phase – CO/H2 (1:1) 40 atm, 24 h resulting in the yields of 56–94% in the ring expansion, and 65–94% in the ring opening of oxetanes.