[NH:1]1[C:8]2[N:4]([N:5]=[CH:6][CH:7]=2)[CH2:3][CH2:2]1.Br[CH2:10][C:11]([O:13][CH2:14][CH3:15])=[O:12].C(=O)(O)[O-].[K+].C(OCC)(=O)C>CS(C)=O.O>[CH2:14]([O:13][C:11]([CH2:10][N:1]1[C:8]2[N:4]([N:5]=[CH:6][CH:7]=2)[CH2:3][CH2:2]1)=[O:12])[CH3:15]
To a solution of 2,3-dihydro-1H-imidazo[1,2-b]-pyrazole (19 g) in dimethylsulfoxide (95 ml) were added ethyl bromoacetate (20.4 ml) and potassium bicarbonate (30 g) under ice-cooling. The mixture was stirred at room temperature for 4 hours. The reaction mixture was poured into a mixture of ethyl acetate (1.5 l) and water (500 ml). The separated organic layer was washed with water and brine, and dried over magnesium sulfate. The solvent was evaporated and the residue was subjected to column chromatography on silica gel using ethyl acetate as an eluent. Fractions containing the object compound were combined and evaporated in vacuo to give 1-ethoxycarbonylmethyl-2,3-dihydro-1H-imidazo[1,2-b]pyrazole (20.3 g).
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