Allene carboxanilide

The aromatic rings of allene carboxanilides 149 also acted as the diene to furnish the tricyclic lactams 150 in refluxing xylene or benzene [125]. 

Diels-Alder reactions have been thoroughly studied, theoretically and mechanistically, and both inter- and mtra-variants are of considerable preparative importance. However, modifications of old reactions are always being made and this year has seen the first reported case in which a monosubstituted benzene ring acts as the diene in an intramolecular [4 + 2] cycloaddition. When heated at 100 °C, with or without solvent, the allene carboxanilides (100) isomerize to pyrrolines (101), which may be crystallized from the reaction mixtures. 

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See also in sourсe #XX -- [ , ]

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