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Triazolines 24 . Permanganate‐catalyzed low temperature thermolysis of 5‐(4‐pyridyl) substituted 1,2,3‐triazolines
Author(s) -
Kadaba Pankaja K.,
Parmley Gordon,
Crooks Peter A.,
Agha Bushra
Publication year - 1993
Publication title -
journal of heterocyclic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.321
H-Index - 59
eISSN - 1943-5193
pISSN - 0022-152X
DOI - 10.1002/jhet.5570300505
Subject(s) - chemistry , potassium permanganate , permanganate , thermal decomposition , imine , anhydrous , catalysis , inorganic chemistry , yield (engineering) , benzene , aryl , organic chemistry , alkyl , materials science , metallurgy
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 1 H ‐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.