Synthesis of a pyrone derivative from carbon suboxide and acetylacetone catalyzed by acetylacetonate-metal complexes.

Bis(pentane-2,4-dionate)-metal, M(acac)2, (where M = Zn, Co, Ni and Cu) reacts quickly and in high yield with carbon suboxide, C3O2, at the methine position. The reaction produces 1:2 adducts which are insoluble in all organic solvents. The reaction of these adducts with aqueous HCl forms 5-acetyl-2-hydroxy-6-methyl-4-pyrone (AHMP). The above-mentioned metal-acetylacetonates also catalyze the addition of C3O2 to free Hacac, but Cr(acac)3, Fe(acac)3 and Mn(acac)3 do not. The relative catalytic efficiency of these pentane-2,4-dionates was determined. A mechanism for these reactions is proposed.