Double Diels-Alder reactions of coumalic acid with 1,3-dienes.

Thermal reaction of coumalic acid with 1,3-butadienes gave after diazomethane treatment dimethyl tricyclo[3.2.1.02,7]oct-3-ene-2,4-dicarboxylate via double Diels-Alder reaction. This represents the simplest synthesis of such a tricyclic system. The reaction with cyclopentadiene was also studied.