A novel example of a natural 2,5-dihydroxyflavanone from Unona lawii

3-Formyl-2,4,6-trihydroxy-5-methyldibenzoylmethane from Unona lawii has been shown to exist in a cyclic hemiketal form whereas 3-formyl-2,6-dihydroxy-4-methoxy-5-methyldibenzoylmethane from the same plant mainly exists in the enolic ring opened form, owing to chelation of both hydroxyl groups. The flavonoid pattern of Unona lawii suggests the biogenetic scheme : flavanone → 2-hydroxyflavanone → flavone. 3-Formyl-2,4,6-trihydroxy-5-methyldibenzoylmethane has been synthesized by Baker-Venkataraman rearrangement of 3-formyl-2,4,6-tri-hydroxy-5-methylacetophenone benzoate.