[Cl:1][C:2]1[CH:3]=[C:4]2[C:9](=[CH:10][CH:11]=1)[N:8]1[CH:12]=[N:13][N:14]=[C:7]1[N:6]=[C:5]2[C:15]1[CH:20]=[CH:19][CH:18]=[CH:17][CH:16]=1.[BH4-].[Na+]>CN(C)C=O>[Cl:1][C:2]1[CH:3]=[C:4]2[C:9](=[CH:10][CH:11]=1)[N:8]1[CH:12]=[N:13][N:14]=[C:7]1[NH:6][CH:5]2[C:15]1[CH:20]=[CH:19][CH:18]=[CH:17][CH:16]=1To a suspension of 2.6 g of 7-chloro-5-phenyl-s-triazolo[4,3-a]quinazoline in 100 ml of dimethylformamide was added 1 g of sodium borohydride. The mixture was stirred at room temperature overnight and then poured into ice-water. The resulting precipitate was collected by filtration, washed with water and dried. The so obtained solid was suspended in a mixture of 30 ml of methanol and 30 ml of concentrated hydrochloric acid, and the mixture was heated under reflux for 40 minutes. After cooling, the resulting mixture was neutralized with ammonia water. The precipitate formed was collected by filtration, washed with water, and recrystallized from methanol to give 1.2 g of 7-chloro-4,5-dihydro-5-phenyl-s-triazolo[4,3-a]quinazoline as colorless prisms, m.p. 241.5°-243.5° C.
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