Synthesis and study of structure of 2-alkenylsulfanylbenzimidazoles

Abstract

Benzimidazole-2-thiol (1) and its derivatives are promising ligands for the synthesis of new organic compounds possessing a broad spectrum of biological activity (vasoconstrictor, antimicrobial, antibacterial, antitumor, antifungal, antiviral, antiulcer, antituberculosis, etc.). Compounds of this series are also used as corrosion inhibitors, antioxidants, and stabilizers in polymer production. In the present paper we have studied the interaction between benzimidazole-2-thiol 1 and methallyl chloride (2a), prenyl bromide (2b), trans-cinnamyl chloride (2c), and (E)-methyl-4-bromobutene-2-oate (2d) in the superbasic KOH–H2O–DMF medium for the first time. It has been found that in all cases the alkylation reactions proceed regioselectively with the formation of individual 2-methallylsulfanylbenzimidazole (3a) (in 70 %yield), 2-prenylsulfanylbenzimidazole (3b) (in 60 % yield), trans-2-cinnamylsulfanylbenzimidazole (3c) (in 65 % yield), and (E)-methyl[4-((benzimidazol-2-yl)thio)butene-2-oate] (3d) (in 21 % yield). The structure of the synthesized compounds 3a–d has been studied and proved by mass spectrometry (GC–MS), as well as IR, ¹H NMR spectroscopy. The mass spectra of all the studied compounds, with the exception of butenoate 3d, contain a peak of the molecular ion [M]+•. General predictable directions for fragmentation of the molecular ions of S-derivatives 3a–c, which are accompanied by elimination of methyl, thiol, and benzimidazolylsulfide radicals, have been revealed. The IR spectra of compounds 3a–d lack vibrational bands of the thiol –SH group, however characteristic vibrational bands of the corresponding aliphatic and alkenyl fragments presented in the structure of the target products have been revealed. The evidence that alkylation reactions of benzimidazole-2-thiol 1 occur at the sulfur atom is the presence of signals for the –SCH2– protons at δ 3.97–4.16 ppm in the 1Н NMR spectra of compounds 3a–d. The detailed 1H NMR spectra analysis has revealed the influence of substituents of different electronic nature on the position of the proton signals of the alkenyl fragments.