The pyrolysis of 2-azidobenzoates. A new synthesis of carbazoles and other N-heterocycles

Abstract

The spray pyrolysis of aryl 2-azidobenzoates yields carbazoles, involving a rearrangement whereby the nitrogen of the product is attached to the aryl 1-carbon, a process involving a spiro 6-membered intermediate. When the aryl ortho-positions were both alkyl substituted the product was an acridan instead. With an ortho-carboxylate, acridone formation competed with that of carbazole. When the CO–O group of the substrate was replaced by O–CO, CO–S, CO–NPh, or SO₂–O the pyrolysis was ineffective. Benzyl 2-azidobenzoates, however, pyrolysed to yield 1-benzyl-2,1 -benzisoxazolones by an unprecedented C–O insertion reaction of the intermediate nitrene.