Hydrochloric Acid → 5,7-Dihydroxyspiro[chroman-2,1'-cyclopropan]-4-one

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Reaction Conditions

Reaction Steps

Under argon, 112 g (690 mmol) of 1,3,5-trihydroxybenzene dihydrate are dissolved in 230 ml abs. dimethylformamide, 28.82 g (230 mmol) of methyl cyclopropylideneacetate (Example 41A) and 20 g of 4 Å molecular sieve (as powder) are added and the mixture is stirred at a bath temperature of 130° C. overnight. 1 liter of 1 N hydrochloric acid is then added, and the mixture is extracted repeatedly with ethyl acetate. The combined organic phases are washed once with water and once with saturated sodium chloride solution, dried over sodium sulfate and concentrated. 230 ml (2.99 mol) of trifluoroacetic acid are added to the product obtained, and the mixture is heated to 75° C. and stirred for 8 hours. The mixture is then cooled, water is added and the mixture is extracted repeatedly with ethyl acetate. The combined organic phases are washed twice with saturated sodium chloride solution, dried over sodium sulfate, filtered and concentrated. The residue is purified on silica gel (mobile phase: dichloromethane/methanol 100:1→100:3). The product fractions are combined and concentrated. Dichloromethane is added to the residue obtained, the mixture is stirred briefly and the precipitate is filtered off with suction and dried under high vacuum. This gives 2.25 g (5% of theory) of the target compound. The mother liquor is then purified again on a silica gel column (mobile phase: dichloromethane/methanol 100:1). This gives a further 3.41 g (7% of theory) of the title compound.

Provenance & Evidence