Polyketoenols and chelates. Glaucyrones and their reactions with magnesium methoxide
Using the pyrone melt procedure of the preceding paper, 3,3′,5,5′-tetrakismethoxycarbonylglaucyrone (2) and the tautomerically unsymmetrical 3′-acetyl-3,5,5′-trimethoxyglaucyrone (5) have been prepared. Conditions can be adjusted to prevent complete ester exchange in the reaction of 3,3′-diacetyl-5,5′-bisethoxycarbonylglaucyrone (1) with excess of magnesium methoxide, in accord with the mechanism proposed. On reaction with the latter reagent, the two new glaucyrones give aromatic penta-esters (11) and (14), and their mechanisms of formation are discussed. Heating these penta-esters effects cyclisation to xanthyrones having aromatic side-chain termini, (13) and (16), respectively.