Combined Directed ortho and Remote Metalation-Suzuki Cross-Coupling Strategies. Efficient Synthesis of Heteroaryl-Fused Benzopyranones from Biaryl O-Carbamates

A concise synthesis of heteroaryl dibenzopyran ones 9a,b, 10a,b, 11a-c, and 12a-c has been achieved by the LDA-induced migration of heterobiaryl O-carbamates 18, 21, 25, and 30 which, in turn, were prepared in good yield using a combined directed ortho lithiation (DoM)-transition-metal-catalyzed Suzuki cross-coupling strategy. An efficient and general route to a wide variety of heterocycles including coumestans 19a,c and the previously unknown isothiocoumestan ring system 22b has been thereby achieved.