THE SYNTHESIS OF ANTHRAPHOS, A CONFORMATIONALLY RIGID, C-2-SYMMETRICAL DIPHOSPHINE AND THE X-RAY CRYSTAL-STRUCTURE OF [RH(COD)(ANTHRAPHOS)]BF4

Anthraphos (trans-9,10-dihydro-9,10-ethanoanthracene-11,12-bis(diphenylphosphine) (3), a conformationally rigid, C-2-symmetric diphosphine, has been prepared in three steps, the key step being the Diets-Alder reaction between anthracene and ethyndiylbis(diphenylphosphine oxide). Resolution of anthraphos followed by formation of the [Rh(COD)(anthraphos)]BF4 complex afforded an optically active hydrogenation catalyst precursor whose crystal and molecular structure and absolute configuration were determined by single crystal X-ray diffractometry. Use of the (R,R)-(-) form of the catalyst precursor to hydrogenate (Z)-alpha-acetamidocinnamic acid gave (S)-(+)-N-acetylphenylalanine in 90% enantiomeric excess.