The cobalt(II) complex of the simple polyketide model methyl 3,5-dioxohexanoate is regioselectively alkylated to afford methyl 4-alkyl-3,5-dioxohexanoates, which cyclize on treatment with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) to give 5-alkyl-4-hydroxy-6-methyl-2-pyrones.
Regioselective C-alkylations at the intercarbonyl positions C-4 and C-2 of the polyketide model methyl 3,5-dioxohexanoate, 1, have been acomplished through reactions of its cobalt(II), 4a, and copper(II), 4b, complexes respectively. Some examples of double alkylations at both positions are presented. Cyclizations of the regioselectively substituted diketoesters so prepared gave triacetic acid lactone