Photoreactions of α-amino ketones derived from heterocyclic secondary amines

Abstract

The photochemical behaviour of N-phenacyl nitrogen heterocycles varies with the size of the heterocyclic ring. U.v. irradiation of 1-phenacylindoline and 2,3,3-trimethyl-1-phenacylindoline resulted in type-II fission to give acetophenone and indole or 2,3,3-trimehyl-3H-indole, respectively. Indole was also produced, along with 2,3-diphenylbutane-2,3-diol, when indoline was irradiated with acetophenone. Both 1-phenacyl- and 1-(2-oxocyclohexyl)-1,2,3,4-tetrahydroquinoline underwent type-II cyclisation to azetidinol derivatives; fission was a minor process. In contrast, on irradiation of 5,6-dihydro-5-phenacylphenanthridine, type-II fission occurred to give acetophenone and phenanthridine. Irradiation of 2,3,4,5-tetrahydro-1-phenacyl-1H-benz[b]azepine resulted in direct homolysis of the N–CH₂CO bond to yield 2,3,4,5-tetrahydro-1H-benz[b]azepine as the major product.