Ck. Ghosh et al., BENZOPYRANS .30. SYNTHESIS OF SUBSTITUTED XANTHONES FROM 3-ACYL-2-METHYL-I-BENZOPYRAN-4-ONES, Tetrahedron, 49(19), 1993, pp. 4127-4134
The xanthone 8 results from the base catalysed self-condensation of th
e chromone 1. The chromone 2 gives the xanthones 9 and 11 with sodium
and DMF-POCl3 respectively, phenol 14 with NaOMe, and the pyran 22 wit
h 2-thiomethylchromone 6. The enamine 16 on Vilsmeier-Haak reaction af
fords the chloroxanthone 12. The pyran 15, isolated as a byproduct fro
m the reaction of omega-acetyl-2-hydroxyacetophenone with HC(OEt)3-AC2
O, affords the xanthone 13 by refluxing with NaOMe in MeOH.