The invention discloses a preparation method of a chiral intermediate (S)-3-methyl-1-tert-butoxycarbonyl-1,4-diazepane for treating
ocular hypertension, relating to the technical field of pharmaceutical chemicals. The invention comprises the following steps: using 1-benzyl-3-methylpiperidin-4-one as a starting
raw material, performing
chiral resolution to obtain an intermediate 1, performing an addition-
elimination reaction on the intermediate 1 and
hydroxylamine hydrochloride to obtain an intermediate 2, performing a
Beckmann rearrangement reaction on the intermediate 2 to obtain an intermediate 3, performing an amino deprotection reaction on the intermediate 3 to obtain an intermediate 4, performing an amino protection reaction on the intermediate 4 and di-tert-butyl
dicarbonate to obtain an intermediate 5, and performing a
decarbonylation reaction on the intermediate 5 to obtain the (S)-3-methyl-1-tert-butoxycarbonyl-1,4-diazepane. The preparation method has the characteristics of readily available raw materials, a simple process and a high product yield, and is suitable for the industrial production of the (S)-3-methyl-1-tert-butoxycarbonyl-1,4-diazepane.