Vinyl Sulfone Bicycloannulation of Cyclohexenones: One-Step Synthesis of Tricyclo2,7>octan-6-ones

Article abstract of DOI:10.1021/jo00195a005

Vinyl sulfones bicycloannulate the α'-enolates of α-cyclohexenones in the presence of hexamethylphosphoramide in refluxing tetrahydrofuran to give tricyclo<3.2.1.0^2,7>octan-6-ones in a single synthetic step.In the case of β-methylcyclohexenones this method gives higher yields than vinylphosphonium bicycloannulation, but with α-methylcyclohexenones theopposite is true.The reaction is successful with both aryl vinyl sulfones and aryl isopropenyl sulfones, but the presence of electron-withdrawing para substituents on the aromatic ring was found to be disadvantageous.Based on the isolation of intermediates and side products, the mechanism of the bicycloannulation is believed to proceed via sequential conjugate addition of the enolate to the vinyl sulfone, intramolecular Michael addition, and expulsion of arene sulfinate anion with formation of the cyclopropane ring.