Lactams. XVII. Synthesis and Stereochemical Characterization of Diethyl cis-and trans-5-Ethyl-2-oxo-4-piperidinemalonate

Abstract

The Michael addition of diethyl malonate to 1-acetyl-3-ethyl-2, 3-dihydro-6 (1H)-pyridone (3) in EtOH at 55° has been found to give the trans isomer (4a) and the cis isomer (4b) of diethyl 5-ethyl-2-oxo-4-piperidinemalonate in a ratio of 85 : 15. The stereochemical assignments were based on C-13 nuclear magnetic resonance spectroscopic evidence as well as chemical interrelation with substances of known configuration. The latter included decarbethoxylation of 4a and 4b in dimethyl sulfoxide-H₂O-NaCl to give the lactam monoesters 5a and 5b, conversion of 4a into trans-1-benzyl-5-ethyl-2-oxo-4-piperidinemalonic acid (7a) through the lactim ether 9a and its benzylated product 8a, debenzylation of 7a with sodium in liquid ammonia to give 6a, and alkaline hydrolysis of 4a to 6a.