H-1 AND C-13 NMR ASSIGNMENTS AND STEREOCHEMISTRY OF D,L-ISOSPONGIADIOL AND 6 SPONGIAN INTERMEDIATES

Long-range (LR COSY, RELAY, TOCSY, HMBC) and neighbor (COSY, HMQC) 2D correlation NMR methods were used in tandem to derive complete H-1 and C-13 NMR assignments for synthetic d,l-isospongiadiol and six spongia n intermediates obtained from a novel free-radical tandem cyclization process. The C-13 NMR spectra of synthetic d,l-isospongiadiol are iden tical with those reported previously for natural isospongiadiol, where as the 1H NMR spectra reflect solvent differences. NOESY and differenc e NOE data demonstrate that synthetic d,l-isospongiadiol and the spong ian intermediates have the desired (19)beta-methylene and 18 alpha-, 1 7 beta-and 20 beta-methyl stereoselectivity at the stereogenic centers , and that rings A-C are in chair conformations. (C) 1998 John Wiley & Sons, Ltd.