An efficient method for the carbonylation of (hetero) aryl pentafluorobenzenesulfonates and triflates under exceptionally mild conditions using palladium/dicobalt octacarbonyl [Pd/Co2(CO)8] has been developed. Besides acting as carbon monoxide (CO) source, Co2(CO)8 enhances the reaction rate by accelerating the CO insertion through an in situ generated bimetallic palladium cobalt tetracarbonyl [Pd‐Co(CO)4] complex. Under the optimized reaction condition, carbonylation of a wide range of activated and deactivated, as well as sterically hindered and heteroaromatic, substrates proceeded efficiently at room temperature. The high chemoselectivity and improved synthesis of biologically relevant Isoguvacine and Lazabemide intermediates highlights its scope as a valuable synthetic method. The generality of this protocol was further extended to other electrophiles (bromides, chlorides and tosylates).magnified image

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Reactions. -The coupling of pentafluorobenzenesulfonates and aryl boronic acids proceeds under mild conditions to give a wide range of biaryls including hindered ortho-substituted derivatives. The process exhibits high chemoselectivity over tosylates, mesylates, and chlorides as shown for substrates (IVd-f). The scope of the synthetic protocol is further extended to alkyl boronic acids. -(JOSEPH, J. T.; SAJITH, A. M.; NINGEGOWDA, R. C.; NAGARAJ, A.; RANGAPPA, K. S.; SHASHIKANTH*, S.; Tetrahedron Lett. 56 (2015) 36, 5106-5111, http://dx.