Vinyl azides in heterocyclic synthesis. Part 4. Thermal and photochemical decomposition of azidocinnamates containing ortho-cycloalkenyl substituents

Abstract

Thermolysis of azidocinnamates containing ortho-cycloalkenyl substituents leads to isoquinolines and benzazepines formed by interception of the azide, or derived vinylnitrene, by the neighbouring double bond, the stability of the azide varying with the ring size of the cyclic alkene substituent. The cycloheptenyl (1a) and cyclopentenyl (1c) azides decompose at room temperature by intramolecular cycloaddition of the azide to the double bond to give products derived from the corresponding triazoline intermediates (9) and (22). Some n.m.r. spectroscopic evidence for the triazoline (9) is obtained. The cyclohexenyl azide (1b) is more stable, and hence requires the decomposition to be carried out at higher temperatures, where the azirine–vinylnitrene products, indole (15) and aziridine (14), are formed in competition with the isoquinoline (12) and the benzazepine (13). Photochemical decomposition of the azides (1b,c) gives tetracyclic cyclopropanes (26) formed by intramolecular cycloaddition of the cyclic alkene to iminocarbene intermediates.