Dimethyl sulphoxide and acetic anhydride convert 4-hydroxycoumarin (1 a) 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] [I] benzopyran-4-one (6a), 2-(2-hydroxybenzoyl) -4H-furo[3,2-c] [ 1 ] benzopyran-4-one 3-(2,3-dihydro-2hydroxymethyl-3-oxobenzo [b] * I ,3,5,7-Tetra-azatricyclo[3.3.1 .13*']decane.
Bei der Umsetzung der Hydroxycumarine (I) mit Acetanhydrid in DMSO werden die Spaltprodukte (II) und daneben die kondensierten Cumarine (III) bzw. (IV) erhalten.
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