Tris(benzimidazo)-1,3,5-triazine from the Thermolysis of 2-Aryloxybenzimidazoles

Abstract

2-Aryloxybenzimidazoles gave tris(benzimidazo)-[1,2-a: 1′,2′-c: 1″,2″-e]-1,3,5-triazine and phenol in almost quantitative yields upon heating at 230–250 °C, while in the reaction in cumene small amounts of 2-aryloxy-1,2′-dibenzimidazole and dicumyl were obtained along with the major products. On the other hand, 2-phenylthiobenzimidazole gave diphenyl disulfide and 1,2′-dibenzimidazole, together with tris(benzimidazo)-1,3,5-triazine. The thermolysis is assumed to proceed by step-by-step radical processes involving the formation of such intermediates as 2-aryloxy-1,2′-dibenzimidazole and 2-aryloxy-1,2′-1′,2″-trisbenzimidazole.

Synthesis of Trinuclear Benzimidazole‐Fused Hybrid Scaffolds by Transition Metal‐Free Tandem C(sp2)−N Bond Formation under Microwave Irradiation

“…Treatment of 1 a with 2-methoxybenzimidazole surrogates, 2-phenoxy-and 2-(2-naphthoxy)benzimidazoles (2 g and 2 h) under the employed conditions gave 3 a in 80 % and 67 % yields, respectively along with concomitant formation of 2naphthol (13) (54 % yield) in the reaction with 2 h (Scheme 4, (3)). [25] Similarly, when 1 o, N-methyl-substituted analogue of 1 a, was treated with 2 h under the optimized conditions, 2-methoxynaphthalene ( 14) by β-elimination was also formed in 9 % yield with concomitant formation of 3 a (16 %) and many unidentifiable products (Scheme 4, ( 4)). benzimidazoles with 2-methoxy-and 2-aryloxybenzimidazoles as building blocks in the presence of CsF under microwave irradiation.…”

“…The following experimental results show an evidence for the extrusion of such an alcohol during the course of reaction. Treatment of 1 a with 2‐methoxybenzimidazole surrogates, 2‐phenoxy‐ and 2‐(2‐naphthoxy)benzimidazoles ( 2 g and 2 h ) under the employed conditions gave 3 a in 80 % and 67 % yields, respectively along with concomitant formation of 2‐naphthol ( 13 ) (54 % yield) in the reaction with 2 h (Scheme 4, (3)) [25] . Similarly, when 1 o , N‐methyl‐substituted analogue of 1 a , was treated with 2 h under the optimized conditions, 2‐methoxynaphthalene ( 14 ) by β‐elimination was also formed in 9 % yield with concomitant formation of 3 a (16 %) and many unidentifiable products (Scheme 4, (4)).…”

“…The products were isolated by TLC (a glass plate coated with Kieselgel 60 GF 254 , Merck). The starting compounds 1 , 4 and building blocks 2 were prepared by known methods [11,14,15,25] . Other commercially available organic and inorganic reagents were used without further purification.…”

Thermally induced oxidative trimerization of benzimidazole by copper(II) chloride in the solid state

“…): C, 72.2 (72.4); H, 3.6 (3.4); N, 24.0 (24.1). The trimer has also been prepared by heating 2-phenoxybenzimidazole at 240ºC for 5 hours as reported earlier [5] for comparison with our product.…”

“…As for example, it photodehydrodimerizes in 1% ethanol to give a mixture of isomers (I and II), which are symmetrical and the reaction probably proceeds through the intermediacy of a 2-bibenzimidazolyl radical. On the other hand, 2{aryloxy benzimidazoles, ¤ Email: ghosh 59@yahoo.com Unauthenticated Download Date | 5/11/18 7:52 AM 2{phenylthiobenzimidazole, thiadiazoles, or 2{chloro benzimidazole, and related derivatives produce a cyclic trimer of the benzimidazolyl residue (III) upon thermolysis [5,6,7,8,9]. Benzimidazole itself does not undergo any such thermal polymerization rather it oxidizes to an unusual compound (IV) by an oxidizing agent such as PbO 2 [1].…”