Reaction of phosphorus-stabilized carbanions with cyclic enones. Aromatization of the substitution and addition products

Abstract

α-Lithiated alkylphosphonic esters react with substituted cyclohex-2-enones either at the carbonyl group (addition yielding 2-hydroxyalkylphosphonic products) or at the β-carbon (addition–elimination yielding δ-keto phosphonates). Both types of products undergo smooth aromatization when treated with I₂ in MeOH or with pyridinium perbromide in AcOH leading to a variety of benzylphosphonic esters substituted in the aromatic ring with the methoxy or hydroxy groups. Mechanisms of the aromatization reactions are discussed.