Cyclization of diethyl 2-acetoacetyl-3-oxoglutarate anion generated in situ by the reaction of diethyl sodio-3-oxoglutarate with diketen

Abstract

Reaction of diethyl sodio-3-oxoglutarate with diketen (4-methyleneoxetan-2-one) in anhydrous tetrahydrofuran under mild conditions provided an intermediate adduct (diethyl 2-acetoacetyl-3-oxoglutarate anion)(2), which immediately cyclized to a γ-pyrone (ethyl 3-ethoxycarbonyl-6-methyl-4-oxo-4H-pyran-2-ylacetate)(3), regarded as a masked form of tetra-acetic acid (3,5,7-trioxo-octanoic acid)(1), and three aldol-type condensation products [ethyl 2-ethoxycarbonyl-3,5-dihydroxyphenylacetate (4), diethyl 2,6-dihydroxy-4-methylisophthalate (5), and ethyl 3-acetyl-2,6-dihydroxy-4-methylbenzoate (6)].