Method for preparing N-methyl 2-(3-pyridyl) (1R,2R)-2-tetrahydrothiopyrancarbothioamide-1-oxide

Process for the preparation of (1R,2R)-N-methyl-2-(3-pyridyl) tetrahydrothiopyran-2-carbo-thioamide 1-oxide of formula:

• ##STR5## wherein a salt of (1 R,2R)-N-methyl-2-(3-pyridyl) tetrahydro-thiopyran-2-carbothioamide 1-oxide with an optically active acid chosen from (-)-camphanic acid and (+)-3-bromo-10-camphorsulphonic acid is selectively precipitated in a solvent chosen from water, aliphatic alcohols containing 1 to 4 carbon atoms and aqueous-alcoholic mixtures, from the salt of a mixture of the (1R,2R)- and (1S,2S)-trans isomers of N-methyl-2-(3-pyridyl)tetrahydrothiopyran-2-carbothioamide 1-oxide with the optically active acid, and the (1R,2R)-N-methyl-2-(3-pyridyl)tetrahydrothiopyran-2-carbothiodiamine 1-oxide is then liberated from its salt.