Direct Resolution of Secondary Tert-Butylphenylphosphine Oxide

Abstract

Secondary phosphine oxides constitute an important class of organophosphorus compounds and are higly useful as versatile phosphinoylating agents and as ligands ^[1,2] They are however not readily available in the optically active form.^[3–5] We wish to demonstrate that P-chiral secondary teri-butylphenylphosphine oxide (I) can be promptly resolved into enantiomers by means of its diastereoisomeric complexes with L-O,O-dibenzoyltanaric acid (L-DBTA) Dissolution of equimolar amounts of racemic I and L-DBTA in the 4 I benzene acetone mixture yields crystalline II complex containing exclusively the R-enantiomer of the starting phosphine oxide The complexed S-enantiomer is obtained from the mother liquor by crystallization from benzene The enantiomers of I are freed from their L-DBTA complexes by simple washing with aqueous NaOH Both enantiomers of 1 of very high optical purity are thus obtained from a single batch These enantiomers have subsequently been tested for their configurational stability in selected synthetic applications.