Photochemistry of Vinyl Halides. Heterocycles from Reaction of Photogenerated Vinyl Cations with Azide Anion

Article abstract of DOI:10.1021/jo00199a003

Irradiation of 1,2,2-tris(p-methoxyphenyl)vinyl bromide (1a-Br) and tetrabutylammonium azide in acetonitrile afforded 1,1,3,4,6,6-hexakis(p-methoxyphenyl)-2,5-diaza-1,3,5-hexatriene (2a).Formation of 2a suggests the presence of azirine 3a as a reactive intermediate and a route to synthesis of heterocycles in combination with azirine photochemistry.Irradiation of α-arylvinyl halides 1 and tetrabutylammonium azide in acetonitrile in the presence of dimethyl fumarate gave 1-pyrrolidine derivatives 5.When the irradiation was performed in acetone, oxazoline derivatives 6 were obtained.The reaction of vinyl halides 1 with azide anion took place succesfully even in a two phase system, i.e., water-methylene chloride-tetrabutylammonium halide as a phase-transfer catalyst.In addition, photolysis of 2,2-bis(p-methoxyphenyl)-1-phenylvinyl bromide (1f-Br) in a two-phase system led to the formation of the β-aryl rearranged pyrrolines 5f.This results indicates strong evidence for the intervention of vinyl cations in the photochemical reaction of the vinyl halide 1 and azide anion.The mechanistic points on the photochemical substitution and the scope and limitation of the reaction are discussed.