Tyrosines, ring expansion

The ring expansion of phenyl azides on irradiation and the concomitant ring expansion to a didehydroazepine and subsequent trapping provides a useful synthetic route to a variety of azepine systems. Thus irradiation of695, with a variety of/7-substituents, occurs readily in THF/water to yield the azepinones 696. Interest in the influence of other substituents on this process has been recorded in the study of the reactions of 3- and 4-nitrophenyl azides" ". This work has illustrated the profound effect that substituents can have on the reaction. Ring expansion is also observed for a tyrosine derivative". Irradiation of 697 in excess diethylamine brings above the exclusive conversion into 698 76. 

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