Triazolines24. Permanganate-catalyzed low temperature thermolysis of 5-(4-pyridyl) substituted 1,2,3-triazolines

Autor: Gordon Parmley, Pankaja K. Kadaba, Bushra J. Agha, Peter A. Crooks
Rok vydání: 1993
Předmět:
Zdroj: Journal of Heterocyclic Chemistry. 30:1191-1195
ISSN: 1943-5193
0022-152X
DOI: 10.1002/jhet.5570300505
Popis: Potassium permanganate oxidation of 1-aryl-5-(4-pyridyl)-1,2,3-triazolines I in a benzene-water two-phase system using the phase-transfer catalyst tetrabutylammonium chloride yields the corresponding 1H-1,2,3-tri-azoles II. However, when the reaction is run in a single phase in anhydrous benzene alone, the products are not triazoles, but imines III that can normally be obtained only by high-temperature thermolysis of the tri-azolines. The presence of both potassium permanganate and tetrabutylammonium chloride to yield the benzene soluble tetrabutylammonium permanganate ion pair appears essential for imine formation, although only in catalytic amounts. Thus a reaction pathway is proposed, which involves the initial coordination of the pyridyl nitrogen with the manganese atom of the permanganate ion leading to IV, followed by loss of nitrogen and regeneration of the permanganate ion via the dihydropyridine intermediates, V and VI, to yield the enamine VII, which tautomerizes to the imine III. Supportive evidence for the formation of IV is derived from the failure of 1,5-diaryl- and l-aryl-5-(3-pyridyl)triazolines to yield the respective imines; they lack the structural requirements necessary to comply with the proposed mechanism, and are recovered unchanged. Unlike the high temperature pyrolysis, the permanganate catalyzed low temperature thermolysis reactions provide cleaner products in better yields. Thus, the low temperature thermolysis may afford a route for the synthesis of clean samples of l-arylimino-l-ethyl-4-pyridines, especially when the triazolines are on hand.
Databáze: OpenAIRE
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