SYNTHESIS AND REACTIONS OF PHOSPHINE BORANES - SYNTHESIS OF NEW BIDENTATE LIGANDS WITH HOMOCHIRAL PHOSPHINE CENTERS VIA OPTICALLY PURE PHOSPHINE BORANES

Secondary and tertiary phosphine-boranes were synthesized in one-pot from phosphine oxides or substituted chlorophosphines without isolation of the intermediate phosphines. Phosphine-boranes having a methyl group were metalated with iec-butyllithium. The generated carbanions reacted with alkyl halides or carbonyl compounds to yield various phosphine-borane derivatives. The carbanions underwent copper(II)-promoted oxidative coupling without impairment of the borane functionality. Secondary phosphine-boranes reacted with alkyl halides, aldehydes, or α,β-unsaturated carbonyl compounds to give phosphine-borane derivatives having a functional group. The boranato group of phosphine-boranes was removed in a stereospecific manner with retention of configuration by treatment with a large excess of amine such as morpholine. A new route to bidentate ligands with homochiral phosphine centers has been explored by utilizing these characteristic reactivities of phosphine-boranes. Thus, optically pure (S, S)-1,2-bis(o-anisylphenylphosphino)ethane, (R, R)-1,2-bis(terr-butylphenylphosphino)ethane, and (S, S)-1,4-bis(o-anisylphenylphosphino)butane have been synthesized via phosphine-boranes. © 1990, American Chemical Society. All rights reserved.