Oxygen-bridged tetrahydropyridines, hexahydropyridines, and dihydropyridones via a Hantzsch-like synthesis with 4-(2-hydroxyphenyl)but-3-en-2-one

Abstract

Substituted oxygen-bridged tetrahydro-2-pyridones and tetrahydropyridines (4) and (7) were synthesized by condensation of 4-(2-hydroxyphenyl)but-3-en-2-one (1) with Meldrum's acid (2) and 3-aminocrotononitrile, respectively, in the presence of ammonium acetate. Analogous cyclo-condensations of (1) with methyl 3-amino-2,4-dicyanobut-2-enoate (8) and methyl 3-amino-2-cyanopentene-2-dioate (10) led to oxygen-bridged hexahydropyridines (9) and (11), respectively, of different stereochemistry in the piperidine rings. The dichotomy in the stereospecific routes to these oxygen-bridged heterocycles is discussed. Preparation of 4-aryl substituted dihydro-2-pyridones is also reported.