Chloroacetaldehyde → 3-Hydroxy-6-(3-nitrophenyl)-7-pyridin-4-yl-2,3-dihydro-pyrazolo[5,1-b]thiazole

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Reaction Steps

5-(3-Nitro-phenyl)-4-pyridin-4-yl-2H-pyrazole-3-thiol (prepared as described in Example 1) (3.92 g, 13.14 mmol) was dissolved in a 1:1 THF/water mixture (130 mL). Chloroacetaldehyde (55% in water, 2.31 mL, 19.71 mmol, 1.5 eq) was added and the solution was stirred at room temperature overnight. The reaction mixture was diluted with AcOEt and saturated aqueous NaHCO3. The organic phase was washed with saturated aqueous NaHCO3 and brine, dried and evaporated to dryness. 3.25 g of crude product were obtained as yellow solid (72%), which was used in the following step without further purification.

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