(R)-(+)-6-isopropenyl-3-methyl-2-cycloheptenone is synthesized from (R)-(-)-carvone by reduction and trialkylsilyl-enolether formation, cyclopropanation with methylene iodide and diethylzinc, followed by a Saegusa type oxidation with ferric chloride and finally dehydrochlorination with base. The title compound is obtained in five steps and 38% overall yield, being a useful chiron for guaiane sesquiterpene natural products.
cycloheptenone; carvone; ring expansion; perhydroazulene; enantioselectivity
