Intramolecular Cyclizations of Vinyl-Substituted N,N-Dialkyl Arylamines Enabled by Borane-Assisted Hydride Transfer

Catalytic amounts of B(C 6 F 5 ) 3 have been found to be able to promote the intramolecular cyclization of vinyl-substituted N, N -dialkyl arylamines to afford nitrogen-containing heterocycles. Our mechanistic studies indicate the reaction is initiated by abstraction of an α-hydride from an N -alkyl substituent by B(C 6 F 5 ) 3, which is followed by cyclization, and is concluded by delivery of the hydride to the cyclic cationic intermediate. The dual roles of B(C 6 F 5 ) 3, first as an oxidant and then as a hydride-carrying reductant, have enabled a rare redox-neutral cyclization process between a sp 3 carbon and an electron-rich olefin without using a transition metal or an external oxidant.