PREPARATION OF A BICYCLIC ANALOG OF QINGHAO (ARTEMISINIC) ACID VIA A LEWIS-ACID CATALYZED IONIC DIELS-ALDER REACTION INVOLVING A HYDROXY DIENE AND CYCLIC ENONE AND FACILE CONVERSION INTO (+ -)-6,9-DESDIMETHYLQINGHAOSU/

Treatment of 6-methylcyclohex-2-enone (8) and hexa-3,5-dien-1-ol (14) either in dichloromethane at -20 to 0 degrees C with aluminum chloride (1 equiv) or in acetonitrile at -20 degrees C with Cu(II) trifluorome thanesulfonate (1 equiv) rapidly provides in a highly stereoselective reaction the hemiacetal Diels-Aider adduct 15, which with a trans ring junction and anti methyl group is considered to arise via an ionic Ga ssman-type Diels-Alder reaction involving prior formation of a hemiace tal between the alcohol and enone followed by generation of an allylic cation from the hemiacetal mediated by the Lewis acid. The adduct 15 is then converted in straightforward fashion into the methyl ester of the desdimethyl analogue of qinghao (artemisinic) acid, which upon seq uential photosensitized oxygenation and then Fe(phen)(3)(PF6)(3)/coppe r(II) triflate catalyzed cleavage-oxygenation provides (+/-)-6,9-desdi methylqinghaosu.