Regiospecific Normal Diels-Alder Reaction of trans-1,2-Biscoumarinylethenes

[摘要]：The reaction of different 7,8-substituted coumarin 4-acetic acids with 7-diethylaminocoumarin-3-carbaldehyde in the presence of piperidine in methanol gives 1,2-biscoumarinylethenes. These compounds undergo regiospecific Diels-Alder reactions at their electron-rich diene components C-3-C-4-C-10-C-9, with electron-deficient dienophiles. The feasibility of normal electron-demand Diels-Alder reactions could be explained on the basis of the HOMO-LUMO gap. All the compounds are new and are intensely colored.

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