Air-Stable CpCoI-Phosphite-Fumarate Precatalyst in Cyclization Reactions: Comparing Different Methods of Energy Supply

The robust Co-I precatalyst [CpCo(P{OEt}(3))(trans-MeO2CHC=CHCO2Me)] was investigated in cyclotrimerizations, furnishing benzenes and pyridines from triynes, diynes and nitriles, comparing the influence of different ways of energy supply; namely, irradiation and conventional (thermal) or microwave heating. The precatalyst was found to work under all conditions, including the possibility to catalyze cyclotrimerizations at room temperature under photochemical conditions at longer reaction times. Performance of the reactions in a microwave reactor proved to be the most time-efficient way to rapidly assemble the expected reaction products; however, careful selection of reaction conditions can be required. The synthesis of pyridines and isoquinolines successfully involved the utilization of versatile functionalized nitriles, affording structurally interesting reaction products. Comparison with the known and often applied precatalyst CpCo(CO)(2) demonstrated the significantly higher reactivity of the CpCoI-phosphite-olefin precatalyst.