Boosting the Enantioselectivity of Conjugate Borylation of α,β-Disubstituted Cyclobutenones with Monooxides of Chiral C(2) -Symmetric Bis(phosphine) Ligands

Chiral bis(phosphine) monooxides (BPMOs) derived from C(2) -symmetric bis(phosphines) have been found to induce superior levels of enantioselection in copper-catalyzed conjugate borylation of α,β-disubstituted cyclobutenones. More precisely, enantiomeric excesses as well as chemical yields are exceedingly high with (R,R)-Bozphos as the chiral ligand while these values are low with parent (R,R)-Me-Duphos. A similar yet less pronounced effect was seen in the corresponding 1,6-addition to para-quinone methides.