(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

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. Copyright (C) 1996 Elsevier Science Ltd