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Synthesis of Bis-Heterocyclic 1H-Imidazole 3-Oxides from 3-Oxido-1H-imidazole-4-carbohydrazides


Pieczonka, A M; Mloston, G; Heimgartner, H (2012). Synthesis of Bis-Heterocyclic 1H-Imidazole 3-Oxides from 3-Oxido-1H-imidazole-4-carbohydrazides. Helvetica Chimica Acta, 95(3):404-414.

Abstract

The reaction of 1H-imidazole-4-carbohydrazides 1, which are conveniently accessible by treatment of the corresponding esters with NH2NH2·H2O, with isothiocyanates in refluxing EtOH led to thiosemicarbazides (= hydrazinecarbothioamides) 4 in high yields (Scheme 2). Whereas 4 in boiling
aqueous NaOH yielded 2,4-dihydro-3H-1,2,4-triazole-3-thiones 5, the reaction in concentrated H2SO4 at room temperature gave 1,3,4-thiadiazol-2-amines 6. Similarly, the reaction of 1 with butyl isocyanate led to semicarbazides 7, which, under basic conditions, undergo cyclization to give 2,4-dihydro-3H-1,2,4-triazol-3-ones 8 (Scheme 3). Treatment of 1 with Ac2O yielded the diacylhydrazine derivatives 9 exclusively, and the alternative isomerization of 1 to imidazol-2-ones was not observed (Scheme 4). It is
important to note that, in all these transformations, the imidazole N-oxide residue is retained. Furthermore, it was shown that imidazole N-oxides bearing a 1,2,4-triazole-3-thione or 1,3,4-thiadiazol-2-amine moiety undergo the S-transfer reaction to give bis-heterocyclic 1H-imidazole-2-thiones 11 by treatment with 2,2,4,4-tetramethylcyclobutane-1,3-dithione (Scheme 5).

The reaction of 1H-imidazole-4-carbohydrazides 1, which are conveniently accessible by treatment of the corresponding esters with NH2NH2·H2O, with isothiocyanates in refluxing EtOH led to thiosemicarbazides (= hydrazinecarbothioamides) 4 in high yields (Scheme 2). Whereas 4 in boiling
aqueous NaOH yielded 2,4-dihydro-3H-1,2,4-triazole-3-thiones 5, the reaction in concentrated H2SO4 at room temperature gave 1,3,4-thiadiazol-2-amines 6. Similarly, the reaction of 1 with butyl isocyanate led to semicarbazides 7, which, under basic conditions, undergo cyclization to give 2,4-dihydro-3H-1,2,4-triazol-3-ones 8 (Scheme 3). Treatment of 1 with Ac2O yielded the diacylhydrazine derivatives 9 exclusively, and the alternative isomerization of 1 to imidazol-2-ones was not observed (Scheme 4). It is
important to note that, in all these transformations, the imidazole N-oxide residue is retained. Furthermore, it was shown that imidazole N-oxides bearing a 1,2,4-triazole-3-thione or 1,3,4-thiadiazol-2-amine moiety undergo the S-transfer reaction to give bis-heterocyclic 1H-imidazole-2-thiones 11 by treatment with 2,2,4,4-tetramethylcyclobutane-1,3-dithione (Scheme 5).

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Department of Chemistry
Dewey Decimal Classification:540 Chemistry
Language:English
Date:March 2012
Deposited On:18 Apr 2012 07:09
Last Modified:05 Apr 2016 15:45
Publisher:Verlag Helvetica Chimica Acta
ISSN:0018-019X
Funders:European Social Fund HUMAN – BEST INVESTMENT! , co-funded by the European Union.
Publisher DOI:https://doi.org/10.1002/hlca.201100470
Permanent URL: https://doi.org/10.5167/uzh-61480

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