First Modular Synthesis of Dissymmetric Biaryldiphosphine Ligands Allowing Tunable Steric and Electronic Effects

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AbstractThe first modular synthesis of a family of C1‐symmetric diphosphine ligands is presented. Their synthesis is based on unprecedented highly regioselective halogen/metal interconversions on a common polybrominated biaryl precursor. This methodology allows the functionalization of the ortho‐ and ortho′‐positions of the biaryl core. Diphosphine ligands carrying only one substituent at the 6‐position and the two phosphine substituents at the 2‐ and 2′‐position become easily accessible. The two phosphine substituents may be identical (as in compounds 2 and 3) or different (as in compounds 1 and 4). All diphosphines were prepared on gram scale, and the enantiopure ligands were obtained by chromatography of the racemate on a chiral HPLC column. The asymmetric hydrogenation of β‐keto esters, acetamidocinnamates and dimethyl itaconate revealed good to excellent asymmetric inductions of up to 99 % ee, and are often close to those of the well‐known C2‐symmetric MeO‐BIPHEP.