Assignment of NMR data and relative stereochemistry determination of paraconic acid derivatives

γ-Butyrolactones 4a1, 4a2, 4b1 and 4b2 were carefully studied through NMR experiments. 1H NMR, 13C {1H} NMR, COSY, HMQC, HMBC and J-res experiments were performed to provide the needed structure information. NOE between protons distributed around the stereocenters were thus used to determine the relative configuration of the molecules.