AbstractSeventeen optically active substituted 1,3,4,5‐tetrahydro‐2H‐1,5‐benzodiazepine‐2‐thiones (1ato1d, 2ato2d, 3dto3d, 4bto4dand5bto5d) were synthesized by treating the corresponding optically active substituted 1,3,4,5‐tetrahydro‐2H‐1,5‐benzodiazepin‐2‐ones with Lawesson's reagent (L. R.). The thioamide1awas alkylated with methyl iodide to obtain 4‐methyl‐2‐methylmercaptodihydro‐1,5‐benzodiazepine (6a) and 4,5‐dimethyl‐2‐methylmercaptodihydro‐1,5‐benzodiazepine‐2‐thione (6b). Twelve optically active substituted 1,3,4,5‐tetrahydro‐2H‐1,5‐benzodiazepines (7ato7c, 8ato8d, 9ato9dand10d) were synthesized by the reduction of the corresponding substituted 1,3,4,5‐tetrahydro‐2H‐1,5‐benzodiazepin‐2‐ones. 4‐Methyl‐1,5‐diacetyl‐(7e) and 1,4,5‐trimethyl‐ (7d), 1,3,4,5‐tetrahydro‐2H‐1,5‐benzodiazepines were synthesized by treating7awith acetic anhydride and methyl iodide separately as given in the experimental part. The UV and CD spectra of the parent chiral benzodiazepines7ato7dand benzodiazepine‐2‐thiones1ato1dare discussed, showing that especially several n → π* transition can be detected via the chiroptical methods only. Sign changes of Cotto