Intermolecular hydroaminations via strained (E)-cycloalkenes

A photoinduced procedure for the intermolecular hydroamination of alkenes using azoles is described. This reaction occurs in modest to good yield for 6- and 7-membered cyclic alkenes. Upon irradiation at 254 nm in the presence of methyl benzoate and a small amount of triflic acid as an additive (20 mol %), imidazoles, pyrazoles, triazoles, and tetrazole can react with the alkene to afford complex Markovnikov adducts. The proposed mechanism involves photoisomerization to generate highly strained (E)-cycloalkene intermediates and (E)-cycloalkene protonation followed by reaction with the azole nucleophile. Alkene isomerization was found to be a competing side reaction under these conditions.