A STEREOSELECTIVE TOTAL SYNTHESIS OF (+/-)-ALLIACOL-A AND CONGENERS OF MARASMIUS-ALLIACEUS

Synthesis of alliacolide(1), alliacol A (2), and 12-noralliacolide (4), members of the alliacane family of sesquiterpene lactones, was accomplished through both syn- and anti-modes of intramolecular S-N' displacement. Two routes to 12-noralliacolide (4) are presented, which contrast brevity and efficiency in stereoselection (i.e. 14 --> 16/17 versus 37a/b --> 38). Since both routes culminate in C-ring annulation, introduction of the correct stereochemical arrangement relied heavily on the structural features of the hydrindane (AB) precursor(s). Choice of the proper AB system 24 facilitated production of tetrahydrofuran 38. With the full skeleton in place, 38 was efficiently epoxidized and oxidized to 4. 12-Noralliacolide (4) served as an appropriate relay substrate for conversion to alliacol A (2) and several other alliacanes.