[CH2:1]([O:3][C:4]([C:6]1[C:7]2[CH2:8][C@@H:9]3[CH2:21][C@@H:10]3[C:11]=2[N:12]([C:14]2[CH:19]=[C:18](Br)[CH:17]=[CH:16][N:15]=2)[N:13]=1)=[O:5])[CH3:2].[ClH:22]>C(#N)C.O>[CH2:1]([O:3][C:4]([C:6]1[C:7]2[CH2:8][C@@H:9]3[CH2:21][C@@H:10]3[C:11]=2[N:12]([C:14]2[CH:19]=[C:18]([Cl:22])[CH:17]=[CH:16][N:15]=2)[N:13]=1)=[O:5])[CH3:2]To a solution of (1aS,5aS)-2-(4-bromo-pyridin-2-yl)-1a,2,5,5a-tetrahydro-1H-2,3-diaza-cyclopropa[a]pentalene-4-carboxylic acid ethyl ester (2.1 g, 6.0 mmol) in acetonitrile (30 mL) was added concentrated HCl (1.4 mL, 18.0 mmol). The reaction was stirred for 6 h at 80° C., and then diluted with H2O. The solid was filtered, washed with H2O, and dried to give (1aS,5aS)-2-(4-chloro-pyridin-2-yl)-1a,2,5,5a-tetrahydro-1H-2,3-diaza-cyclopropa[a]pentalene-4-carboxylic acid ethyl ester (1.7 g) which contained ˜20% of the hydrolyzed acid. The aforementioned ester was dissolved in dioxane (10 mL). After addition of 1 N LiOH (9.0 mL), the reaction was stirred for 4 h at 40° C. The reaction was cooled down to room temperature, diluted with H2O, and acidified with 4 N HCl to form a precipitate. The solid was filtered, washed with H2O, and dried to give the title compound. LCMS m/z=276.1 [M+H]+.
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