The structure of aryl-substituted cis-1-thiadecalins formed together with 5,6-tetramethylenethiopyrylium salts in disproportionation reactions of condensed 4H-, 6H-thiopyrans and dihydrothiopyrans with CF3COOH, as well as in the ionic reduction of the latter by the ion pair trifluoroacetic acid-triethylsilane, was studied. It was shown that the reduction proceeds stereospecifically with the formation of configurationally and conformationally homogeneous aryl-cis-1-thiadecalins possessing 2α-R1- and 2α-R1-4α-R2-configurations. The configurational and conformational assignments were made by the 13C NMR method.