SYNTHESIS AND ASYMMETRIC DIELS-ALDER REACTION OF DIMETHYL (D-ISOBORNEOL-10-SULPHINYL)MALEATE - NOVEL ROUTE TO KEY INTERMEDIATES FOR SYNTHESIS OF SOME CARBOCYCLIC NUCLEOSIDES AND TERPENOIDS

The chiral sulphoxide 1 was synthesized from 10-mercaptoisoborneol via diastereoselective oxidation. The dienophile 1 reacted with cyclopentadiene in the presence of a Lewis acid to give the adducts 7 and 8 with high diastereoselectivity (approximately 100%). Diels-Alder reaction of 1 in the absence of a Lewis acid afforded the adduct 9 as the major product with reversed diastereoselectivity. The adduct 7 was transformed into a useful precursor 11 for synthesis of carbocyclic nucleosides. The adducts 7 and 9 were converted into a bridged bicyclic lactone 21 in an enantiodivergent manner via selective reduction followed by reaction with samarium diiodide.