Isocyanates carbonylnitrenes

Photolysis of carbonyl azides gives rise to two types of reactions. The photo-Curtius rearrangement proceeds to form isocyanate. In addition, bimolecidar trapping products, typical of the reactions of singlet carbonylnitrenes, are also observed. 

The yields of the isocyanates produced upon photolysis of benzoyl azide (R=Ph, 31b) and its pam-methoxy, para-chloro and meta- uoro derivatives were found to be in the range of 40-50% in both inert solvents and in solvents that intercept acylnitrenes. Similar results were obtained for 2-naphthoyl azide (35). Irradiation of 35 in cyclohexane at room temperature produces isocyanate (36, -45%), A-cyclohexyl-2-naphthamide - the product of 2-naphthoylnitrene (37) insertion (-50%), and a trace (<1%) of 2-naphthamide (38). Therefore, it was concluded that carbonylnitrenes (R-CO-N) do not rearrange to isocyanates (R-N=C=0) at a rate that is competitive with their capture by trapping agents. ... 

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