THE SYNTHESIS OF 1,5-DIARYL-4-ARYLTHIOPYRROLIDIN- 2-ONES BY ARYLSULFЕNYLATION OF STYRYL ACETIC ACID N-ARYLAMIDES
The role of the electrophilic intramolecular cyclization (EIC) reaction of unsaturated carboxylic acid amides has been described for the design of arylthio-containing lactams and lactones. In order to identify the effect of the styryl moiety on regioselectivity of the electrophilic intramolecular cyclization process styryl acetic acid amides with electron-donating substituents in para-position of the styryl moiety have been studied. It has been found that these compounds react with phenyl and p-tolylsulfenylchlorides in nitromethane in the presence of lithium perchlorate as a “doping additive” to form 1,5-diaryl-4-arylthiopyrrolidin-2-ones with the yield of 60-66%. It is most likely that the reaction found includes the formation of the episulfonium cation stabilized by the perchlorate-anion followed by 5-endo-cyclization onto the nitrogen atom of the amide group. The structure of the compounds synthesized has been confirmed by their spectral parameters. In particular, the IR-spectra contain strong absorption bands C=O at 1703-1703 cm-1, and 1H NMR-spectra of the compounds obtained are characterized by two protons multiple shifts of the H3 pyrrolidine ring at 2.52-2.64 and 3.08-3.22 ppm, respectively, H4 proton multiple shifts at 3.61-3.76 ppm and H5 at 4.99-5.09 ppm. Formation of the pyrrolidine ring as a result of cyclization has been reliably proven by 13C NMR-spectra with the typical signals of carbon atoms: C3 (37 ppm), C4 (48 ppm), C5 (69 ppm) and C2 (172 ppm).