Photochemical reactions Curtius rearrangement

Acyl azides are well-known compounds. Their role in the thermal Curtius rearrangement, a reaction that apparently does not involve a nitrene, will be discussed in subsection 8.3.2. Photochemical decomposition of acyl azides elidts nitrene reactivity. In particular, intramolecular C-H-insertion reactions have been observed, but not usually in high 5deld. ... 

The synthesis of 4,5-difluoroimidazole has also been described by Kirk using a photochemical Schiemann reaction (Scheme 59) [74]. Curtius rearrangement of the acyl azide, prepared in two steps from ethyl 4-fluoroimidazole-5-carboxylate via hydrazide, afforded the key intermediate Boc-protected 5-fluoroimidazol-4-carboxylate. In situ Boc deprotection followed by diazotization of the amine and photolysis of the diazonium tetrafluoroborate afforded 4,5-difluoroimidazole. 

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