Reactions of polysubstituted thiopyrans with proton acids and structural studies of the resulting thiacyclohexanes

Abstract

Depending on the number and nature of substituting groups, 4H-thiopyrans under the influence of perchloric and trifluoroacetic acids either undergo disproportionation or form thiapyrylium salts in quantitative yields with the participation of air oxygen; in the case of ionic hydrogenation with CF₃COOH-SiHEt₃ they are converted to thiacyclohexanes, regardless of their structure. To ascertain the reason for the difference in the mechanisms of the reaction of polysubstituted thiopyrans with proton acids the structures of the polysubstituted thiacyclohexanes were investigated jointly by NMR spectroscopy and x-ray diffraction analysis; this made it possible to form a judgment regarding the effect of the degree and character of substitution of 4H-thiopyrans on the mechanism of their reaction with proton acids. The tetrahydrothiopyran ring has a chair conformation. The phenyl substituents are equatorially oriented, while the methyl substituents are axially oriented.