Dienophiles dimethylacetylene dicarboxylate

The results reported in Table 24 indicate that the reactions can be complete or almost complete when strong dienophiles (e.g. N-phenylmaleinimide, fumaro nitrile of dimethylacetylene dicarboxylate) are used. Howewr, the dienophiles listed in Table 24 are not the most reactive with cyclopentadiene and hence long reaction times and an excess of dienophile is necessary to approach the reaction completeness. 

Diphenylacetylene is a less reactive dienophile than dimethylacetylene-dicarboxylate but when heated with tetraphenylcyclopentadienone without solvent a temperature (ca. 380-400°C) suitable for reaction can be attained. In the following procedure the dienophile is taken in large excess to serve as solvent. Since refluxing diphenylacetylene (bp about 300°C) keeps the temperature below the melting point of the product, removal of the diphenylacetylene lets the reaction mixture melt, which ensures completion of the reaction. 

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