It was found that the heating of 3,7-dimethyl-5-thianonan-2,8-dione at 50 degrees C in ethanol in the presence of potassium hydroxide yields 1,4,5-trimethyl-7-thiabicyclo[2.2.2]octan-2-one as a mixture of 5-exo- and 5-endo-isomers in the ratio of 5 : 1. The oxidation of thiabicyclooctanone with hydrogen peroxide and its reduction with sodium borohydride result in 1,4,5-trimethyl-7-thiabicyclo[2.2.2]octane-2-one-7,7-dioxide and 1,4,5-trimethyl-7-thiabicyclo[2.2.2]octane-2-ol, respectively.