The stable planar conformation of the γ-butyrolactone ring in solution

The conformations of γ-butyrolactone ring in solution were deduced on the basis of 1H NMR spectra of geminal protons of the butyrolactone ring. A series of optically pure (Z)-(−)-4-(1′-alkoxyl-1′-carbalkoxy-methylene)-5(R)[(1R)-menthyloxy]-γ-butyrolactones with a stable planar conformation of γ-butyrolactone ring were found.