The treatment of 5-formyl-1,3,6-trimethyl-2,4(1H,3H)-pyrimidinedione (1) with a magnesium salt and DBU in dichloromethane gave the corresponding magnesium dienolate. The dienolate underwent [4+2] cycloaddition reaction with olefinic dienophiles in highly regio- and stereoselective manners.
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Yasue et al. (1992) studied this question.