Pd-Catalyzed Direct Arylations of Heteroaromatics using Aryl Sulfonates

Significance

Reported is a palladium-catalyzed direct arylation of heteroarenes (benzoxazole, oxazole, caffeine, 1,2,3-triazole) with aryl tosylates. The first examples of direct arylation using mesylates as arylating reagents are also described. This cross-coupling involves the use of Pd(OAc)₂/X-Phos as a catalytic system and K₂CO₃ as a base. In the case of benzoxazole, the addition of a catalytic amount of t-BuCO₂H improves the coupling. The scope of the reaction has been studied with electron-rich and electron-poor aryl tosylates and mesylates to give products in 58-99% yields. Single examples of an ortho-substituted aryl tosylate and an alkenyl tosylate were also described.