O-SILYLATION OF SOME UNSATURATED CYCLIC PHOSPHINE OXIDES

The phosphoryl oxygen of 1.6-dihydrophosphinine oxides is silylated rapidly at room temperature by bis(trimethylsilyl)trifluoroacetamide; the product loses a ring proton to establish the resonance stabilized γ 5 -phosphinine ring system. Similar events take place with a 3-keto derivative of a tetrahydrophosphinine oxide, which also undergoes silylation of the keto oxygen. 1,4-Dihydro-lazaphosphinine are silylated to give 1,4-aza-γ 5 -phosphinines; their dibenzo derivatives (5,10-dihydrophenophosphazine oxides) require more forcing conditions (triethylsilyl bromide at 100°C) for phosphoryl silylation. These conditions are also effective for silylation of a 3-phospholene oxide.