Isomeric oxatricyclodecanones with non-planar lactone groups: Synthesis, absolute configuration, NMR and X-ray study

Abstract

Several rigid polycyclic lactones, potentially suitable as models for investigation of the lactone grouping geometry, were synthesized. (3S)-4-Oxatricyclo[4.3.1.03,7]decan-5-one ((+)-I), (3R)-5-oxatricyclo[4.3.1.03,8]decan-4-one ((+)-III) and (4S)-5-oxatricyclo[5.2.1.04,8]decan-6-one ((-)-VIII) were prepared by acid-catalyzed lactonization of (2R)-endo-bicyclo[2.2.2]oct-5-ene-2-carboxylic acid. (1S)-4-Oxatricyclo[4.4.0.03,8]decan-5-one ((-)-II) was synthesized from (2S, 5S)-endo,endo-bicyclo[2.2.2]-octane-2,5-dicarbolyxic acid. The structure of VIII was unequivocally proved by its NMR, spectra and the geometry of III was determined by X-ray analysis. The absolute configuration of (+)-III was assigned by correlation with (1R)-bicyclo[3.2.1]nonan-6-one. The acid-induced interconversion of I, II, III and VIII was studied. Lactones II and III represent suitable rigid models for investigations of non-planar lactone groups of known chirality and geometry.