1.2.4- Triazole, 1-phenyl-, pyrolysis isoindole

On pyrolysis, 1-arylimidazoles rearrange to 2-arylimidazoles. In other systems pyrolysis causes more deep-seated changes. 1-Arylbenzotriazoles on pyrolysis or photolysis give carbazoles via intermediate nitrenes (see Section 3.4.1.2.1). 1-Phenyl-1,2,4-triazole (714) is pyrolyzed to isoindole... 

Synthesis of benzo[c]furans and isoindoles (181) is also possible by the addition of benzyne to the respective monocycles (178), followed by reduction (179 — 180) and pyrolysis. In an alternative procedure, (179) is reacted with 3,6-bis(2-pyridyl)-l,2,4,5-tetrazine, which affords (181) under far less vigorous conditions via a retro Diels-Alder reaction of the intermediate (182). 4-Phenyl-1,2,4-triazoles pyrolyze to form isoindoles (Section 3.4.3.12.2). 

A species which may be described either as an iminocarbene54 or a nitrile ylide (52) is formed by gas-phase pyrolysis of 1-phenyl-l,2,4-triazole (Eq. 14). The rearrangement, leading to isoindole, was rationalized in terms of a 1,5-phenyl shift followed by nitrogen extrusion from the 3ff-triazole 51.54... 

Isoindole has been detected (by trapping it with iV-phenylmaleimide) in the pyrolysis of 1-phenyl-1,2,4-triazole at 800°C (Section III,F).18... 

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