Symmetrical molecules from reaction of beta-cyclohexanediones with acetylenedicarboxylic acid in aqueous medium

In an attempt to obtain Michael adducts in aqueous medium, 1,3-cyclohexanedione (1) or dimedone (2) and acetylenedicarboxylic acid monopotassium (3) were dissolved in water and heated to reflux. Under these conditions, two products were isolated from the reaction mixture between 1 and 3: 2-[1-(2,6-dioxocyclohexyl)ethyl]-1,3-cyclohexanedione (6) and a xanthenedione (7), which corresponds to the cyclization of 6. The reaction between 2 and 3 gave only the 2-[1-(4,4-dimethyl-2,6-dioxocyclohexyl)ethyl]-5,5-dimethyl-1,3-cyclohexanedione (8).