N[C:2]1[CH:3]=[CH:4][C:5]2[N:9]=[C:8]3[CH2:10][CH2:11][CH2:12][N:7]3[C:6]=2[CH:13]=1.N([O-])=O.[Na+].[ClH:18]>O>[Cl:18][C:2]1[CH:3]=[CH:4][C:5]2[N:9]=[C:8]3[CH2:10][CH2:11][CH2:12][N:7]3[C:6]=2[CH:13]=1A suspension of 17.3 g of 7-amino-2,3-dihydro-1H-pyrrolo [1,2-a]benzimidazole prepared according to W. Reppe, Ann. 596, 209 (1955) in 200 cm3 of 5 N hydrochloric acid is diazotized with a solution of 7.2 g of sodium nitrite in 30 cm3 of water. The obtained solution is added to a solution of 8 g of cuprous chloride in 35 cm3 of concentrated hydrochloric acid at 50°-60°C. After cooling the precipitate is sucked off, washed with water and suspended in water. By adding to this suspension a 25 % aqueous solution of ammonia the heterocyclic base is set free and sucked off. After drying, recrystallization from benzene yields 4.1 g of 7-chloro-2,3-dihydro-1H-pyrrolo[1,2-a]benzimidazole. Melting point: 136°C.
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