An investigation of the chemistry of lithiotriphenylphosphineacetylmethylene

Abstract

The y1ide anion, lithiotriphenylphosphenylacetylmethylene was obtained by treatment of triphenylphosphineacetylmethylene with 1.2 molecular equivalents of n-butyllithium in tetrahydrofuran-hexane under a nitrogen atmosphere at -78º. This ylide anion reacted selectively with alkyl halides to form γ-substituted 13-keto phosphonium ylides. Subsequent ionization of triphenylphosphine-(3-phenylpropionyl)methylene with n-butyllithium at -78° followed by alkylation produced γ,γ-disubstituted ylides. Condensation of the ylide anion with various aldehydes and ketones afforded δ-hydroxy-β-keto ylides in reasonable yields, uncontaminated by normal Wittig products. Reaction of the ylide anion with o-phthalaldehyde resulted in terminal aldol condensation accompanied by an intramolecular Wittig reaction to give 4,5-benzotropone. The condensation of lithiotriphenylphosphineacetylmethylene with 2-cyclohexene-1-one gave the 1,2-addition product, although it could not be completely purified. Attempts to form potassiotriphenylphosphineacetylmethylene by means of potassium amide in liquid ammonia gave the unexpected product, acetonyldiphenylphosphine oxide. An earlier proposed mechanism for this reaction was partially verified by detection of benzene as a by product. An unidentified compound was isolated from these potassium amide reactions.