A general stereoselective approach to 1,2,4-triazepane-3-thiones/ones via reduction or reductive alkylation of 2,4,5,6-tetrahydro-3H-1,2,4-triazepine-3-thiones/ones

A general stereoselective approach to previously unknown 1,2,4-triazepane-3-thiones/ones based on reduction or reductive alkylation of readily available 2,4,5,6-tetrahydro-3H-1,2,4-triazepine-3-thiones/ones has been developed. The approach involved treatment of tetrahydrotriazepines with sodium cyanoborohydride in MeOH at pH 3 or with sodium borohydride and excess of carboxylic acid in THF to give 1-unsubstituted or 1-alkyl-substituted 1,2,4-triazepane-3-thiones/ones, respectively. The latter were also prepared by reaction of 1-unsubstituted 1,2,4-triazepane-3-thiones/ones with sodium cyanoborohydride and aldehyde in MeOH in the presence of AcOH.