Advanced Tetracycles in a Stereoselective Approach to <i>d,l</i>-Spongiatriol and Related Metabolites: The Use of Radicals in the Synthesis of Angular Electrophores

Abstract

A stereoselective radical cascade cyclization of polyene 6, containing an α,β-unsaturated cyano group, was employed to control six contiguous chiral centers and to introduce a C-8 angular CN group in tricycle 7. The cyano group was ultimately utilized as an entry to a C-8 angular hydroxymethyl group. Compound 7 was converted into two key tetracycles 22 and 25, respectively, each possessing an intact D-furan ring system and containing the necessary functionality for further chemical elaboration to the highly oxygenated spongians 1-5.