1,4-Dimethyl-2,5-dioxabicyclo[2.2.1]heptane-3,6-dione: optical resolution, absolute configuration and circular dichroism

The title dilactone has been resolved into its enantiomers (+)-(S,S)-1 and (–)-(R,R)-1, whose absolute configurations were found by X-ray diffraction analysis of intermediate lactonic amide 2a; the magnitude of the n–π^* Cotton effect increased with an increase in folding or a diminution in twist of the boat conformation of a dilactone ring.