Synthese von Heterocyclen durch C–C‐Knüpfung. III. Heterocyclensynthesen durch intramolekulare En‐Reaktion

Synthesis of Heterocyclic Compounds by C–C-bond Closure. III. Syntheses of Heterocyclic Compounds by Intramolecular En-reaction Cyclohexenyl-acrylamides 1, bearing an alkyl or phenyl group at nitrogen, undergo cyclization to hexahydroindolones 2 on heating above 200°. The reaction follows the pattern of an intramolecular En-reaction. Methacrylic acid, crotonic acid, fumaric acid or maleic acid may be part of the starting molecule in place of acrylic acid; cyclopentenyl-amides may be used in place of cyclohexenyl-amides. Pyrrolidone-3-acetic acids 16 undergo rearrangement to piperidone-4-carboxylic acids 17 on heating in the presence of strong alkali.