Designing Chiral Monodentate Ligands Devoid of Rigid Stereogenic Elements: the Residual Enantiomers of C3 Symmetric P-centered Propellers

Residual stereoisomerism is a form of stereoisomerism discovered by Mislow in the seventies which does not involve any rigid stereogenic element. Chirality is due to the activation of a preferred stereomerization process.1 In light of possible applications of residual enantiomers as ligands for transition metals in stereoselective reactions, some C3 phosphanes and phosphane oxides which could exist as residual antipodes were synthesized. Some of them were obtained in an enantiopure state, structurally characterized and absolute configuration descriptors suggested. Configurational stability of residual enantiomers was assessed by CD decay and DNMR spectroscopy.2 The influence of steric and electronic properties on configurational stability has been investigated. Phosphane oxides display a much higher configurational stability than the corresponding phosphanes. Reported below is the first tris-chiral residual tris-arylphosphane obtained in an enantiopure state.