In contrast to well-known transformations of vinyl azides via azirine intermediates or initiating at the alkene moiety, herein we report a Rh(I)-catalyzed coupling reaction of vinyl azides with isonitriles at the azide moiety to form active vinyl carbodiimide intermediates and following tandem cyclization with unsaturated compounds, such as alkynes and benzynes, to give different classes of azaheterocycles. Mechanistically, controlled experiments and DFT calculations disclose that Rh-nitrene is the vital species in the first coupling step, and the Rh(I) catalyst can also play an important role in the cyclization step of alkynes.
The electrophilic fluorination of unsaturated compounds provides a reliable approach to the generation of organofluorides, which are used widely in agrochemicals, pharmaceuticals, and other materials. Numerous active electrophilic fluorine reagents, such as the fluorine molecule (F 2 ) or xenon difluoride (XeF 2 ), have been applied in fluorination. However, these reagents suffer from their hazardous, toxic, corrosive, and poor selective properties, and the relatively weak electrophilicity of Selectfluor or N-fluorobenzenesulfonimide (NFSI) usually limits their broad applications. Herein, we disclose nitromethane (MeNO 2 ) as an efficient activator of Selectfluor and NFSI, as well as a stabilizer of carbocations.Therefore, the fluoro-azidation, fluoroamination, fluoroesterification of styrenes, and C-H fluorination of (hetero)arenes were well realized just by the facilitation of MeNO 2 . The mild reaction conditions and practicability made our current method a versatile protocol for accessing organofluorides.
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