title: Synthesis of o-Alkenylated 2-Arylbenzoxazoles via Rh-Catalyzed Oxidative Olefination of 2-Arylbenzoxazoles: Scope Investigation, Structural Features, and Mechanism Studies.
abstract: 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.
authors.affiliation: Department of Chemistry, Fudan University , 220 Handan Road, Shanghai 200433, China.
authors.forename: Quan
authors.initials: Q
authors.lastname: Zhou
authors.affiliation: Department of Chemistry, Fudan University , 220 Handan Road, Shanghai 200433, China.
authors.forename: Jing-Fan
authors.initials: JF
authors.lastname: Zhang
authors.affiliation: Department of Chemistry, Fudan University , 220 Handan Road, Shanghai 200433, China.
authors.forename: Hui
authors.initials: H
authors.lastname: Cao
authors.affiliation: Department of Chemistry, Fudan University , 220 Handan Road, Shanghai 200433, China.
authors.forename: Rui
authors.initials: R
authors.lastname: Zhong
authors.affiliation: Department of Chemistry, Fudan University , 220 Handan Road, Shanghai 200433, China.
authors.forename: Xiu-Feng
authors.identifier: 0000-0001-7513-4650
authors.initials: XF
authors.lastname: Hou