Synthese und Struktur von Meldrums Olefin/Synthesis and Structure of Meldrum’s Olefin

Diisopropylidene ethylenetetracarboxylate, Meldrum’s olefin (4, Mel2) has been prepared from [HNEt3][(Mel)2CSMe] (8) and Meldrum’s acid (1, MelH2) in moderate yield. The X-ray analysis of 4 reveals a centrosymmetrical structure in which the two six-membered rings are folded along their carboxylate carbon axes by 34.9°) and linked by a conventional C-C double bond [1.3501(19) Å ]. The “unsymmetrical” structure of 8 is also discussed.