Arylnitrenes: A synthetic approach towards amino-imino-azepines

Abstract

<p>The chemistry of substituted phenylnitrenes was investigated to discern the mechanism and factors involved in the preparation of 3H-dihydroazepines. Synthetic utility of this phenylnitrene reaction was explored through the photolysis of a series of non-symmetric phenylazides. Phenylnitrene production via the photolysis or thermolysis of phenylazides as well as through the deoxygenation of aryl-nitro compounds was compared. Results indicated the photolysis reaction was superior in yielding azepine products. The intermediates involved in the ring expansion reaction of the phenylnitrenes were computer modelled using a semi-empirical molecular orbital calculation that aided in the prediction of the observed product yields. In addition, the azirine intermediates derived from the photolysis of diamido-phenylazides were chemically trapped in situ confirming their presence in the complicated phenylnitrene mechanism. Kinetic data from the chemical trapping of the intermediates formed from the photolysis of 3-acetamido-4-trifluoroacetamido-phenylazide showed the azirine intermediate was formed directly from the singlet phenylnitrene. The didehydroazepine intermediate was formed from the azirine intermediate and not directly from the singlet phenylnitrene. The computational data were used to determine the substituents necessary to preferentially yield the desired azepine product. Finally, in an attempt to synthesize an amino-imino-azepine, 4,5-substituted 3H-dihydroazepines were synthesized selectively from 3,4-substituted phenylazides. However, attempts at oxidizing and/or deprotecting the 3H-dihydroazepines failed because of the harsh reaction conditions employed.</p>