Synthesis of a new enantiomerically pure P-chiral phosphine and its use inprobing the mechanism of the Mitsunobu reaction

A new enantiomerically pure P-chiral phosphine, (S)-cyclohexylmethyl-(1-nap hlhyl)phosphine (1) was prepared by phosphine-borane methodology and used i n a mechanistic study of the Mitsunobu reaction. Enantiomerically enriched (S)-cyclo-hexylmethyl(1-naphtyl) phosphine oxide (8) is obtained if the rea ction proceeds through the phosphonium salt 4, whereas the intermediate dia lkoxyphosphorane 5 leads to racemic phosphine oxide 8. The results of the e xperiments including the variation of the reaction conditions and the natur es of alcohol and carboxylic acid used in the Mitsunobu reaction prove the competition of two alternative mechanisms (reaction via 4 or 5) on the seco nd stage of the Mitsunobu reaction. (C) Wiley-Liss, Inc.