The reactions of 4-hydroxy-2-pyrones with 2-hydroxybenzaldehydes. A note of warning

The reaction between 2-hydroxybenzaldehyde and 4-hydroxy-6-methyl-2-pyrone (triacetic acid lactone) affords 3-acetoacetyl-2-chromenone, 7 , instead of 3-(2-hydroxybenzylidene)-6-methyl-3,4-dihydro-2H-pyran-2,4-dione, 6 . The structures previously reported in the literature for the products formed in the reactions of 4-hydroxy-2-chromenone with 2-hydroxybenzaldehydes in a molar ratio 1:1 are considered erroneous. Thus, the previously reported 3-(2-hydroxybenzylidene)chroman-2,4-dione, 10 , should be formulated as 3-(2-hydroxybenzoyl)-2-chromenone, 11 .