PHOTOLYTIC RING-EXPANSIONS OF 4-AZIDOQUINOLINES AND 6-AZIDODIAZINES: SOME UNEXPECTED AZEPINE RING-OPENING REACTIONS

Article abstract of DOI:10.1016/S0040-4020(01)89775-1

Photolysis of 6-azidoquinazoline in MeOH-KOMe-dioxan yields 8,9-dihydro-5,7-dimethoxy-5H-pyrimido<5,4-c>azepine (5) which on acid hydrolysis ring-opens to the pyrimidine-carbaldehyde (7).The mechanism of formation of this unexpected dimethoxypyrimido-azepine is discussed and related to previous similar results involving 6-azido-2,3-dihydrofuro- and 6-azido-2,3-dihydrothieno<2,3-b>quinolines. In contrast, 6-azidoquinoxaline and 6-azido-2-chloro-4-methylquinoline on photolysis under similar conditions undergo ring expansion to the expected pyrazino<2,3-c>- and pyrido<3,2-c>azepines (22a) and (17) respectively.However, photolysis of the latter azide in MeOH-dioxan yields the 3-(2-pyridyl)propenonitrile derivative (18) in a reaction analogous to that undergone by 6-azidophenazine.