N-bromobutanimide → 5-(5-Bromo-2-propoxyphenyl)-1,6-dihydro-1-methyl-3-propyl-7H-pyrazolo[4,3-d]pyrimidin-7-one

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Reaction Steps

N-Bromosuccinimide (2,6g, 0.016 mol) in dimethylformamide (40 ml) was added dropwise to a stirred solution of 5-(2-n-propoxyphenyl)-1-methyl-3-n-propyl-1,6-dihydro-7H-pyrazolo[4,3-d]pyrimidin-7-one (Preparation 10, 4.0 g, 0.010 mol) in dimethylformamide (40 ml) at room temperature. After 7 hours the solvent was removed by evaporation under vacuum, the residue suspended in saturated aqueous sodium carbonate solution, and the resulting solution extracted with ethyl acetate (3×50 ml). The organic extracts were combined, dried (Na2SO4) and evaporated under vacuum. Trituration of the residue with ether, followed by crystallisation from ethyl acetate-hexane, gave the title compound as white crystals (3.39 g, 68%), m.p. 117°-118° C. Found: C,53.15; H,5.03; N,13,78. C18H21BrN4O2 requires C,53,34; N,5.22; N,13.82%.

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