Atropoenantiomerism of the Z-adduct of 2,3-diethoxycarbonyi-6,6-dimethyl-5,6-dihydro-4-pyridone with dimethyl acetylenedicarboxylate: synthesis and structure in solution and in the crystal

Abstract

The title adduct (1) was synthesized, and its conformationally and configurationally rigid chiral structure in solution and in the crystal was established by NMR spectroscopy and by X-ray structural analysis. Atropoenantiomers of1 were observed by the1H NMR method in the presence of a chiral shift reagent. A barrier to their interconversion was determined, ΔGx > Z5 kcal mol−1 (200 °C).