The cyclocondensation of N-(prop-2-yn-1-yl)-o-phenylenediamines with phenyl isothiocyanate leads to the formation of 1-(prop-2-yn-1-yl)-1,3-dihydro-2H-benzimidazole-2-thiones irrespective of the substituent nature at the triple bond. Reactions of both mono- and diacetylenic derivatives of o-phenylenediamine with carbon disulfide in the presence of KOH proceed with the formation of two heterocyclic nuclei simultaneously. From N-(prop-2-yn-1-yl)-o-phenylenediamines containing an aryl substituent at the triple bond, and N-(penta-2,4-diyn-1-yl)-o-phenylenediamines 2-methylidene-2,3-dihydro[1,3]thiazolo[3,2-a]benzimidazoles are formed. The latter are readily isomerized under the action of base giving thiazolo[3,2-a]benzimidazoles. The cyclocondensation of N-(alk-2-yn-1-yl)-o-phenylenediamines with CS2 leads to [1,3]thiazino[3,2-a]benzimidazoles.
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The authors are deeply grateful to associate professor S. I. Selivanova for recording the NMR spectra. The authors thank the Saint-Petersburg State University for financial support (Research grant 18.104.22.1681).
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