Indole from 1-phenyl-1,2,4-triazole

The 1-azirines obtained from the vapor phase pyrolysis of 4,5-disubstituted 1-phthalimido-1,2,3-triazoles (157) have been found to undergo further thermal reactions (71CC1S18). Those azirines which contain a methyl group in the 2-position of the ring are cleaved to nitriles and phthalimidocarbenes, whereas those azirines which possess a phenyl substituent in the 2-position rearrange to indoles. 

Hydroxymethylene)-2-phenyl-5(4//)-oxazolone 392, obtained from 404, can be used to prepare indoles 408, pyrazoles 409, and fused 1,2,4-triazoles 411 by reaction with phenyUiydrazines or heteroaryIhydrazines. ° Selected examples are shown in Scheme 7.132. 

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