Organophosphorus intermediates. Part III. The base-catalysed addition of methyl phenylphosphinate, dimethyl phosphonate, and diphenylphosphine oxide to tetraphenylcyclopentadienone

Abstract

Methyl phenylphosphinate adds to tetraphenylcyclopentadienone (tetracyclone) in the presence of base with initial formation of a stable enolate anion (1), which on protonation gives 1,4-Michael addition products of predominantly cis-geometry. Dimethyl phosphonate behaves similarly but gives, in addition, considerable quantities (35%) of enol phosphates which are believed to arise by attack of the tervalent tautomer of the diester at carbonyl oxygen atom. Diphenylphosphine oxide adds in a 1,6-manner to the ketone in the presence of base.

The enolate anions (1) are oxidised by an excess of tetracyclone to a stable radical species.

The mechanism of nucleophilic attack on tetracyclone is discussed and the data obtained in this and previous studies in this series are used to assign structures to the complex mixture of products obtained in the reaction of phenylphosphinic acid, phenylphosphonous bismorpholinamide, and tetracyclone.