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Ring contraction of 1,3-diphenylbenzo[1,2,4]triazinyl radicals to 1,2-diphenylbenzimidazoles

Berezin, Andrey A. and Koutentis, Panayiotis A. 2014. Ring contraction of 1,3-diphenylbenzo[1,2,4]triazinyl radicals to 1,2-diphenylbenzimidazoles. Organic and Biomolecular Chemistry 12 (10) , pp. 1641-1648. 10.1039/C3OB42130A

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Reductive ring contraction of 1,3-diphenyl-1,4-dihydrobenzo[e][1,2,4]triazin-4-yls (Blatter's radicals) using zinc powder (2 equiv.) in acetic acid heated to ca. 118 °C gives 1,2-diphenylbenzimidazoles in high yield. 1,3-Diphenylbenzo[e][1,2,4]triazin-7(1H)-one and the zwitterionic tetraphenylhexaazaanthracene (TPHA) also undergo reductive ring contractions to give 1,2-diphenylbenzimidaz-6-ol and 1,2,6,7-tetraphenyl-1,7-dihydrobenzo[1,2-d:4,5-d′]diimidazole, respectively. By using less zinc, the incomplete reduction of TPHA gave the stable organic radical 1,3,7,8-tetraphenyl-4,8-dihydro-1H-imidazo[4,5-g][1,2,4]benzotriazin-1-yl. Imidazolo-, oxazolo- and thiazolo-fused 1,2,4-benzotriazinyls all undergo zinc mediated ring contractions to give imidazolo-, oxazolo- and thiazolo-fused benzimidazoles in excellent yields.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Chemistry
Publisher: Royal Society of Chemistry
ISSN: 1477-0520
Date of Acceptance: 8 January 2014
Last Modified: 20 Jan 2020 15:00

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