2-Alkyl-5,5-dimethyl-1,3,2-dioxaphosphorinan-2-ones α-lithiated carbanions. Synthesis, stability, and conformation

Abstract

The preparation and a conformational study of lithiated 2-alkyl-5,5-dimethyl-1,3,2-dioxaphosphorinan-2-ones (2) in THF–hexane are described. These anions are present as two rapidly interconverting species with the PO bond either axial (2a) or equatorial (2e). They are thermally unstable, but can be stabilised by the presence of one equivalent of LiBr or of lithium di-isopropylamide. A ³¹P NMR study of the self condensation of the carbanions (2) showed that the phosphorus atom in the axial conformation (2a) is more electrophilic than in the equatorial one (2e). An X-ray structural study of 2,5,5-trimethyl-1,3,2-dioxaphosphorinan-2-one is described.