ADVANCED TETRACYCLES IN A STEREOSELECTIVE APPROACH TO D,L-SPONGIATRIOL AND RELATED METABOLITES - THE USE OF RADICALS IN THE SYNTHESIS OF ANGULAR ELECTROPHORES

A stereoselective radical cascade cyclization of polyene 6, containing an alpha,beta-unsaturated cyano group, was employed to control six co ntiguous chiral centers and to introduce a C-8 angular CN group in tri cycle 7, The cyano group was ultimately utilized as an entry to a C-8 angular hydroxymethyl group, Compound 7 was converted inter two key te tracycles 22 and 25, respectively, each possessing an intact D-furan r ing system and containing the necessary functionality for further chem ical elaboration to the highly oxygenated spongians 1-5.