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

Photolysis of 6-azidoquianazoline in MeOH-KOMe-dioxan yields 8,9-dihydro-5,7-dimethoxy-5H-pyrimido[5,4-]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-23-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,-c3- and pyrido[3,2-c]azepines (22a) and (17) respectively. However, photolysis of the latter oxide in MeOH-dioxan yields the 3-(2-pyridyl)propenonitrile derivative (18) in a reaction analogous to that undergone by 6-azidophenazine. © 1990.