Organic photochemical reactions-V. Photorearrangement of anthranils into azepines

Article abstract of DOI:10.1016/0040-4020(69)80041-4

The photolysis of anthranils (III) led to ring enlargement with the formation of 3-acyl-2-methoxy-3H-azepines (IV). The reaction in ether containing water or amines yielded the corresponding 2-oxo- or 2-amino-3H-azepines (V or VII). On the other hand, photolysis of some 7-substituted 3-phenylanthranils (IX and XIII) gave the corresponding 9-acridanone derivatives (X and XIV). A hypothetical scheme (anthranil → nitrene → azirene → azepine) similar to that proposed by Huisgen and Appl for the analogous ring enlargement of phenylazide is applicable to the anthranil rearrangement. By UV and IR spectroscopic methods, the last step was proved to involve a dark reaction of an intermediate (probably azirene species) with protic solvents.