Preparation of a bicyclic analogue of qinghao (artemisinic) acid via a Lewis acid catalyzed ionic Diels - Alder reaction involving a hydroxy diene and cyclic enone and facile conversion into (plus or minus)-6, 9-desdimethylqinghaosu

Reaction between 6-methylcyclohex-2-enone and hexa-35-dien-1-ol in dichloromethane/aluminium chloride or in acetonitrile/Cu(III) trifluoromethane sulfonate produces a hemiacetal Diels-Alder adduct, which helps produce the methylester of the desdimethyl analogue of quinghao (Artemisinic)acid. The adduct formation involves a Lewis acid-catalyzed ionic Gassmann-type Diels-Alder reaction. The hemiacetal Diels-Alder adduct undergoes a photosensitized oxygenation followed by a Fe(phen)3(PF6)(3)/Cu(II) triflate-induced cleavage-oxygenation, producing plus or minus-6,9-desdimethylqinghaosu.