(R)- and (S)-6,6′-dimethyl- and 6,6′-dimethoxy-2,2′-diiodo-1,1′-biphenyls: Versatile intermediates for the synthesis of atropisomeric diphosphine ligands

Abstract Starting from enantiomerically pure 6,6′-dimethyl- or 6,6′-dimethoxy-2,2′-diiodo-1,1′-biphenyls ( 1a or 1b ) a variety of atropisomeric diphosphine ligands of defined axial chirality are directly accessible in good yields: asymmetric diphosphines of type B and the corresponding diphosphines with one (type C ) or two (type D ) stereogenic phosphorus atoms. Pitfalls of the lithiation/phosphination reaction are discussed. The number of P-chiral diastereomers can be reduced by thermal epimerization.