Improved synthesis of thiazolo-, thiadiazino-benzimidazole derivatives

Abstract

An improved synthetic method was investigated for some bridgehead nitrogen heterocycles - thiazolo- or thiadiazino-benzimidazoles. 2-Mercaptobenzimidazole(2-benzimidazolethiol) was prepared by the treatment of o-phenylenediamine with carbon disulfide following the method of Van Allan and Deacon. Thiazolo-3,2-a-benzimidazol-3(2H)-one, thiazolo-3,2-a-benzimidazole-2,3-diones, 1,2,4-dithiazolo-3,2-a-benzimidazol-3-one were synthesized using ring closure reaction of 2-benzimidazolethiol with chloroacetyl chloride, oxalyl chloride, chlorocarbonylsulfenyl chloride, respectively. These heterocyclic compounds were obtained in the hot carbon tetrachloride solution as the result of the suspension reaction without the hydrochloric acid trapping agents. 2- {(Alkyl- or Aryl-amino) carbonyl] thio} benzimidazoles were prepared by the treatment of 2-benzimidazolethiol with alkyl- or aryl-isocyanate in pyridine. The ring closure reaction of these carbamates with phosgene and thiophosgene resulted in 1,3,5-thiadiazino-3,2-a-benzimidazole-2,4-diones and their sulfur analogues, respectively. These heterocyclic compounds were obtained in the ether/$Et_3N$ solution and in the carbon tetrachloride solution. Better yields were obtained in the ether/$Et_3N$ solution.