The reaction of dimethyl sulphoxide and acetic anhydride with 4-hydroxycoumarin and dicoumarol

Abstract

Dimethyl sulphoxide and acetic anhydride convert 4-hydroxycoumarin (1a) into the acetate but at 120 °C this is further transformed into the ylide 3-dimethylsulphoniochroman-2,4-dionate (2). At 160 °C the reaction affords dicoumarol (3a) and other products derived from this by further reactions. These products are 2,3-dihydro-2-(2-hydroxybenzoyl)-4H-furo[3,2-c][1] benzopyran-4-one (6a), 2-(2-hydroxybenzoyl)-4H-furo[3,2-c][1] benzopyran-4-one (11a), 3-(2,3-dihydro-2-hydroxymethyl-3-oxobenzo[b]furan-2-ylmethyl)-4-hydroxycoumarin (13), and 2,3-dihydro-2-(2-hydroxybenzoyl)-2-hydroxymethyl-4H-furo[3,2-c][1] benzopyran-4-one (12a). Compound (6a) is readily dehydrogenated to give compound (11a), which is identical with a known compound obtained by treating dicoumarol with iodine in ethanol. Pyrolysis of compound (12a) affords (6a); pyrolysis of compound (13) affords the spiran (14).

Spectroscopic studies did not establish the structure of compound (6a) unequivocally and the compound failed to give the appropriate positive responses to iorn (III) salts and Gibbs' dichlorobenzoquinonechloroimine reagent because the dihydrofuran system reduced these reagents, the furan (11a) behaving normally. Chemical evidence for structure (6a) depends mainly upon the ability of boron trichloride to regenerate this compound from its methyl ether.