Synthesis of o‑Alkenylated 2‑Arylbenzoxazoles via Rh-Catalyzed Oxidative Olefination of 2‑Arylbenzoxazoles: Scope Investigation, Structural Features, and Mechanism Studies

2-Arylbenzazoles are promising molecules for potential applications in medicine and material areas. Efficient protocols for direct regioselective functionalization of 2-arylbenzoxazoles are in high demand. Herein, we disclose a general method for selective ortho-olefination of 2-arylbenzo­[d]­oxazoles with alkenes enabled by versatile Cp*Rh­(III) in high yields. This protocol features broad functional group tolerance and high regioselectivity. Intermolecular competition studies and kinetic isotope effect experiments imply that the oxidative olefination process occurs via an electrophilic C–H activation pathway. The molecular structure of the m-fluoro-substituted olefination product confirms regioselective C–H activation/olefination at the more hindered site in cases where the meta F atom or heteroatom substituent existed. Apparent torsion angles were observed in the structures of mono- and bis-olefination products, which resulted in distinct different chemical shifts of olefinic protons. Additionally, two gram-scale reactions and further transformation experiments demonstrate that this method is practical for synthesis of ortho-alkenylated 2-arylbenzoxazole derivatives.