title: Novel photoreactions of 2-aza-1,4-dienes in the triplet excited state and via radical-cation intermediates. 2-aza-di-pi-methane rearrangements yielding cyclopropylimines and N-vinylaziridines.
abstract: Triplet-sensitized irradiation of 2-aza-1,4-dienes affords N-cyclopropylimines via 2-aza-di-pi-methane (2-ADPM) rearrangement pathways. In the case of the pentaphenyl-substituted azadiene 1, irradiation leads to formation of cyclopropylimine 2 as well as N-vinylaziridine 3. The transformations represent the first examples of di-pi-methane rearrangement reactions that yield three-membered heterocyclic products. SET-sensitized irradiation of 2-aza-1,4-dienes, by using 9,10-dicyanoanthracene (DCA) as an electron-acceptor sensitizer and biphenyl as cosensitizer, brings about regioselective formation of N-vinylaziridines. Under these conditions, azadiene 1 also affords cyclopropylimine 37, resulting from an aryl-di-pi-methane rearrangement. This result demonstrates that di-pi-methane reactions can also take place via radical-cation intermediates. In some instances, imine and olefin centered cation-radical intermediates, generated by SET-sensitized irradiation, undergo alternative reactions to produce isoquinoline and benzoazepine products.
authors.affiliation: Departamento de Quimica Organica I, Facultad de Ciencias Quimicas, Universidad Complutense, 28040-Madrid, Spain. darmesto@quim.ucm.es
authors.forename: Diego
authors.initials: D
authors.lastname: Armesto
authors.forename: Olga
authors.initials: O
authors.lastname: Caballero
authors.forename: Maria J
authors.initials: MJ
authors.lastname: Ortiz
authors.forename: Antonia R
authors.initials: AR
authors.lastname: Agarrabeitia
authors.forename: Mar
authors.initials: M
authors.lastname: Martin-Fontecha
authors.forename: M Rosario
authors.initials: MR
authors.lastname: Torres