2-Methyl 4-phenyl 3,4-dihydrobenzo(1:5) thiazepine hydrochloride (Ⅲa) is prepared by condensing o-aminothiophenol hydrochloride with 1-phenyl but-2-en-3-one. Attempted conversion of Ⅲaa into its free base with 10% sodium hydroxide resulted in the formation of the amino ketone Ⅵ, which can be transformed back to Ⅲa on treatment with an-hydrous hydrogen chloride. Ⅲa is reduced readily to the corresponding tetrahydro derivative by sodium borohydride. 2,2,4-Trimethyl-2,3,4,5-tetrahydrobenzo (1:5)thiazepine could also be obtained by the reduction of the corresponding 2,3-dihydro-compound with sodium borohydride. However, the dihydrocompound was stable in alkaline solution.