Ruthenium (II) Catalyzed C(sp2)−H Bond Alkenylation of 2‐Arylbenzo[d]oxazole and 2‐Arylbenzo[d]thiazole with Unactivated Olefins.

Functionalization of the bio‐relevant heterocycles 2‐arylbenzo[d]oxazole and 2‐arylbenzo[d]thiazole has been achieved through Ru(II)‐catalyzed alkenylation with unactivated olefins leading to selective formation of the mono‐alkenylated products. This approach has a broad substrate scope with respect to the coupling partners, affords high yields, and works for gram scale synthesis using a readily available Ru‐based catalyst. Mechanistic studies reveal a C−H activation pathway for the dehydrogenative coupling leading to the alkenylation. However, the results of the ESI‐MS‐guided deuterium kinetic isotope effect studies indicate that the C−H activation stage may not be the rate‐determining step of the reaction. The use of a radical scavenging agent such as TEMPO did not show any detrimental effect on the reaction outcome, eliminating the possibility of the involvement of a free‐radical pathway. [ABSTRACT FROM AUTHOR]