Flash‐vacuum pyrolysis of 1‐acylbenzotriazole: Direct observation of cyclopenta‐2,4‐dienylidenemethaneimines by tandem mass spectrometry and low‐temperature infrared spectrometry

Abstract

A real-time analysis of the flash-vacuum pyrolysis products of 1-acetylbenzotriazole (1) and I-benzoylbenzotriazole (2) was performed by tandem mass spectrometry. In the temperature range 50(MOO0C, these compounds lose nitrogen, yielding N-acetyl-and N-benzoylcyclopenta-2,4-dienylidenemethaneimines (10 and 17, respectively). At higher pyrolysis temperatures, 1 gives 2-methylbenzoxazole, cyanocyclopentadiene, methylcyanocyclopentadiene(s), benzonitrile and ketene, which were identified by collision-activated dissociation mass spectrometry. Lowtemperature infrared experiments confirmed the pyrolytic transformation l(2) -+ lO(17) at mediated temperatures.

Chemical Activation in Azide and Nitrene Chemistry: Methyl Azide, Phenyl Azide, Naphthyl Azides, Pyridyl Azides, Benzotriazoles, and Triazolopyridines

“…The apparent absence of CA under mild FVT conditions is ascribed to the fact that the initial products are not nitriles but ketenimines 87 and 88, formed in a Wolff-type rearrangement. [68] The ketenimines cannot easily undergo any sigmatropic rearrangements. The tautomerization to cyanopyrroles is likely to take place during workup and/or during collisions with the walls of the pyrolysis tube, which would help dissipate the excess energy.…”

The chemistry of isatins: a review from 1975 to 1999

“…Ion a usually looses HCN, leading to a fulvene ion (ion b). An arene aziridine is also observed (ion c), which arises from a second loss of CO [544][545][546] . The ions b and c are also observed in the gas-phase pyrolysis of isatin 547 .…”

Formation of Cumulenes, Triple-Bonded, and Related Compounds by Flash Vacuum Thermolysis of Five-Membered Heterocycles

“…[27] While detection of the ketenimine 27 in FVT reactions has not been achieved, it has been accomplished by IR and mass spectrometry in the FVT of the acetyl and benzoyl derivatives at 500Ϫ600°C (32 Ǟ 33). [29] At higher temperatures, decomposition and rearrangement products are formed from the acetyl derivative; they include ketene, cyanocyclopentadiene 28/29, methylcyanocyclopentadiene, benzonitrile, and 2-methylbenzoxazole (34) (up to 24% yield). [29] The latter compound is also obtained in over 90% yield by FVT of the benzisoxazole 35.…”

“…[29] At higher temperatures, decomposition and rearrangement products are formed from the acetyl derivative; they include ketene, cyanocyclopentadiene 28/29, methylcyanocyclopentadiene, benzonitrile, and 2-methylbenzoxazole (34) (up to 24% yield). [29] The latter compound is also obtained in over 90% yield by FVT of the benzisoxazole 35. [30] There was no mention of ring-contraction products in this work.…”