Marco Cereghetti

(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.

An efficient access to (R)- and (S)-6,6′-dimethoxy-2,2′-diiodo-1,1′-biphenyl

Abstract In a better procedure than the known for (rac)-2a, the diamine (rac)-2b was resolved for the first time with the new resolving agent (R,R)- and (S,S)-2,3-di(phenylamino-carbonyl)tartaric acid (5c) (40–45% weight yields; >99% ee). The diamines (R)- or (S)- 2a and 2b were converted with >98% stereochemical retention into the diiodides (R)- and (S)- 3a and 3b and subsequently, without loss of optical purity, diphenylphosphinated to the known diphosphines (R)- and (S)- 4a and 4b.