A new type of C2-symmetric bisphospine ligands with a cyclobutane backbone: practical synthesis and application.

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[reaction: see text] A highly efficient and practical optical resolution of anti-head-to-head racemic coumarin dimer, (+/-)-5, by molecular complexation with TADDOL (6) through hydrogen bonding and a convenient transformation of enantiopure 5 to a new type of C(2)-symmetric bisphosphine ligand (3) have been achieved. The asymmetric induction efficiency of these chiral bisphosphine ligands was evaluated in Pd-catalyzed asymmetric allylic substitution, affording the allylic substitution products in excellent yield (up to 99%) and enantioselectivity (up to 98.9% ee).