1,6-ASYMMETRIC INDUCTION UTILIZING ASYMMETRIC DESYMMETRIZATION BY DIASTEREOSELECTIVE C-O BOND FISSION OF THE 4-SUBSTITUTED BICYCLIC ACETAL - APPLICATION TO A SYNTHESIS OF (-)-FRONTALIN

1,6-Asymmetric induction was achieved in the acid-induced diastereosel ective acetal cleavage reaction of a ii-substituted bicyclic acetal 8 bearing a chiral sulfinyl group. On treatment with titanium tetrachlor ide and 2,6-disubstituted pyridine bases, 8 gave a synthetically versa tile 3,3-disubstituted dihydropyran derivative 9a with moderate diaste reoselectivity. The utility of this chiral synthon was successfully de monstrated by a formal synthesis of (-)-frontalin.