Reaction between dialkyl acetylenedicarboxylates and six-membered 1,3-diketones in the presence of trialkylamines: a convenient synthesis of alkyl 2,5-dioxo-5,6,7,8-tetrahydro-2H-chromene-4-carboxylates

The reaction of dialkyl acetylenedicarboxylates with six-membered cyclic 1,3-diketones such as 1,3-cyclohexanedione or 5,5-dimethyl-1,3-cyclohexanedione in the presence of a catalytic amount of trimethylamine, triethylamine or tributylamine in CH₂Cl₂ leads to alkyl 2,5-dioxo-5,6,7,8-tetrahydro-2H-chromene-4-carboxylates in good yields.