Potassium Hydroxide → 3-(4-Chlorophenyl)-7-hydroxy-2-isopropyl-chromen-4-one

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Reaction Steps

A mixture of 2-(4-chlorophenyl)-1-(2,4-dihydroxyphenyl)-ethanone (100 g, 0.382 mol), iso-butyric acid anhydride (380 ml, 2.29 mol) and dry pyridine (380 ml, 4.69 mol) is stirred at 140° C. for 12 h and then allowed to cool to room temperature. The volatile components are removed in vacuo, and the resulting dark brown oil is dried under high vacuum to give crude isobutyric acid 3-(4-chlorophenyl)-2-isopropyl-4-oxo-4H-chromen-7-yl ester. To a mixture of this crude ester and methanol (400 ml) is added aqueous KOH (250 ml, 5 M) [CAUTION: EXOTHERM]. The dark solution is stirred for 1.5 h, and the methanol is then evaporated in vacuo. The resulting solution is acidified with 2 M HCl to pH 3 to give a brown precipitate, which is removed by filtration. The brown solid is washed with water (3×) and isopropyl ether and then air-dried. The remaining aqueous solution is extracted with ethyl acetate (4×), and the combined organic phases are washed with water (3×), dried (Na2SO4) and evaporated to give a red oil, which solidifies to give a brown solid. The brown solid is washed with isopropyl ether and air-dried. The combined aqueous phases are extracted again (ethyl acetate) to provide a third crop of product.

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