tert-Butyl (6S)-4-hydroxy-6-isobutyl-2-oxo-1,2,5,6-tetrahydropyridine-1-carboxylate and tert-butyl (4R,6S)-4-hydroxy-6-isobutyl-2-oxopiperidine-1-carboxylate.

X-ray studies reveal that tert-butyl (6S)-6-isobutyl-2,4-dioxopiperidine-1-carboxylate occurs in the 4-enol form, viz. tert-butyl (6S)-4-hydroxy-6-isobutyl-2-oxo-1,2,5,6-tetrahydropyridine-1-carboxylate, C14H23NO4, when crystals are grown from a mixture of dichloromethane and pentane, and has an axial orientation of the isobutyl side chain at the 6-position of the piperidine ring. Reduction of the keto functionality leads predominantly to the corresponding beta-hydroxylated delta-lactam, tert-butyl (4R,6S)-4-hydroxy-6-isobutyl-2-oxopiperidine-1-carboxylate, C14H25NO4, with a cis configuration of the 4-hydroxy and 6-isobutyl groups. The two compounds show similar molecular packing driven by strong O-H...O=C hydrogen bonds, leading to infinite chains in the crystal structure.