Stereoselective hetero-Diels-Alder reactions: structure determination of new xanthenedione derivatives by NMR spectroscopy and x-ray crystallography

The proton and carbon spectra of chromane derivatives were completely assig ned by the use of H-1, C-13 and 2D NMR spectroscopy, including NOESY and 2D INADEQUATE. The unambiguous configurational assignments of all regioisomer s were achieved via 2D NOESY. The structure of the regioisomer 7A was confi rmed using x-ray diffraction. (C) 1999 John Wiley & Sons, Ltd.