Flash‐vacuum pyrolysis of nitroarylbenzotriazoles. A tandem mass spectrometry study

Abstract

Tandem mass spectrometry (MS/MS) has been applied to investigate the behaviour of 1‐(2‐nitrophenyl)benzotriazole [8] upon flash‐vacuum pyrolysis (FVP) conditions. Above 500°, 8 is pyrolyzed to give a mixture of 1‐nitrocarbazole [11], 1‐hydroxycarbazole [12] and carbazole [13] Under similar conditions, 2‐(2‐nitrophenyl) benzotriazole [9] appears to be more stable; it is however partially isomerized into 8 at high temperatures. Aza analogs of 8, like 1‐(2‐nitro‐4‐pyridyl) benzotriazole [10] also loose nitrogen above 500° to give a mixture of 1‐nitro‐3‐azacarbazole [19], 1‐hydroxy‐3‐azacarbazole [16] and 3‐azacarbazole [17].

Flash Vacuum Pyrolysis of Azides, Triazoles, and Tetrazoles

“…The same products are formed on FVP of 2-vinylbenzotriazole 459 above 650 °C, thereby suggesting the occurrence of a 1,5-sigmatropic rearrangement of 459 to 454 (eq ). Pyrolytic 1,5-shifts converting 2-ethylbenzotriazole and 2-(2-nitrophenyl)­benzotriazole to the corresponding 1-substituted benzotriazoles have been reported. , …”

“…Cyclizations of 1-(2-pyridyl)- and 1-(1-isoquinolyl)­benzotriazoles afford pyridobenzimidazoles (eqs and 90). 1-(2-Nitro-4-pyridyl)­benzotriazole affords 1-nitro-γ-carboline (1-nitro-3-azacarbazole), but partial loss of the nitro group also occurs, giving γ-carboline and 1-hydroxy-γ-carboline; 2-(2-nitrophenyl)­benzotriazole was found to isomerize in part to 1-(2-nitrophenyl)­benzotriazole …”

“…385 1-(2-Nitro-4-pyridyl)benzotriazole affords 1-nitro-γcarboline (1-nitro-3-azacarbazole), but partial loss of the nitro group also occurs, giving γ-carboline and 1-hydroxy-γ-carboline; 2-(2-nitrophenyl)benzotriazole was found to isomerize in part to 1-(2-nitrophenyl)benzotriazole. 386 FVP of 1-phenyltetrahydrobenzotriazole 445 at 590−630 °C results in cyclization to tetrahydrocarbazole 446 (17%) as well as Wolff-type rearrangement to the ketenimine 447, which was trapped with water to yield the corresponding N-phenylcyclopentanecarboxamide in 20% yield (eq 91). 387 5.3.3.…”

“…31 Pyrolytic 1,5-shifts converting 2-ethylbenzotriazole and 2-(2-nitrophenyl)benzotriazole to the corresponding 1substituted benzotriazoles have been reported. 386,396 FVP of The 2-methylpropenyl derivative 460 afforded the ketenimine Ph−NCCMe 2 461 as the major product at 650 °C, and no indole was formed. At higher temperatures, methacrylonitrile 464, 2-methylpropionitrile 463, and benzene were formed, and these compounds were also formed on pyrolysis of PhNCCMe 2 461 itself (Scheme 62).…”