Experimental and theoretical investigation in the stereoselective synthesis of P-stereogenic phosphine oxides
Résumé
An efficient enantioselective strategy for the synthesis of variously substituted phosphine oxides has been developed, incorporating the use of (1S,2S)-2-aminocyclohexanol as the chiral auxiliary. The method relies on three key steps: 1) Highly diastereoselective formation of PV oxazaphospholidine, rationalized by a theoretical study; 2) highly diastereoselective ring-opening of the oxazaphospholidine oxide with organometallic reagents that takes place with inversion of configuration at the P atom; 3) enantioselective synthesis of phosphine oxides by cleavage of the remaining P[BOND]O bond. Interestingly, the use of a PIII phosphine precursor afforded a P-epimer oxazaphospholidine. Hence, the two enantiomeric phosphine oxides can be synthesized starting from either a PV or a PIII phosphine precursor, which constitutes a clear advantage for the stereoselective synthesis of sterically hindered phosphine oxides.