A practical asymmetric synthesis of sitagliptin phosphate, from 1-(3-(trifluoromethyl)-5,6-dihydro-[1,2,4]triazolo-[4,3a]pyrazin-7(8H)-yl) -4-(2,4,5-trifluorophenyl)butane-1,3-dione, in overall 65.3% yield has been reported. The target compound was synthesized via eneamination, diastereoselective reduction, amine-deprotection, and phosphatization. The key diastereoselective reduction was performed with NaBH4 and ZnCl2, and it gave the product with almost quantitative yield and 68.5% d.e. value after simple work-up and recrystallization with IPA/PE; a high enantiopurity (d.e.% = 99.3%) can also be obtained in 57.1% yield.