Thermal reactions of aryl azides with trans-1,2-dibenzoyl- and trans-1,2-diacetyl-ethylene. Reactivity of 4,5-dibenzoyl- and 4,5-diacetyl-1-aryltriazolines

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Abstract
Thermal reactions of 4-substituted phenyl azides (1) with trans-1,2-dibenzoyl-(DBE) and trans-1,2-diacetyl-ethylene (DAE) have been investigated in benzene solution at room temperature and at 110 °C. These reactions lead to decomposition products of unstable 4,5-diacyl-1-aryltriazolines (14A and B) which have generally escaped isolation except in one case. At room temperature triazolines (14A and B) undergo formal elimination of an aldehyde moiety to give 4-acyltriazoles (3A and B), isomerization to diazo diones (15A and B) from which 1-arylamino-1,2-diacylethylenes (2A and B) are eventually formed, and oxidation to diacyltriazoles (10A and B). At 110 °C 1-arylamino-2,2diacylethylenes (12A and B) and N-aryl-N-vinylamides (13A and B), the rearrangement products occurring via aryl-group migration, are preferentially produced. Under these conditions varying amounts of pyrrolidines (11A and B) also occur. These compounds (11A and B) are ascribed to cycloaddition reactions of azomethine glides resulting from ring opening of intermediate aziridines (16A and B) with DBE or DAE. However, decomposition of triazolines (14A and B) in the presence of triethylamine leads exclusively to the enamines (2A and B). The possible reaction mechanisms involved in the formation of the observed products are discussed.

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