Enantioselective Oxidative Homo- and Cross-Coupling of 2-Naphthols Catalyzed by Chiral Iron Phosphate Complexes

1,1`-bi-2-naphthols (BINOLs) are an important class of compounds. The synthesis of optically pure BINOLs with C<sub>1</sub>-symmetry generally requires the induction of asymmetry by a chiral catalyst via an oxidative radical-anion coupling mechanism. Asymmetric synthesis of the BINOLs, especially having no substitution at 3, 3` positions is the most challenging process due to competitive oxidative racemization of resulting BINOLs. To address this issue, a novel chiral iron phosphate system has been developed and for the first time successfully applied for synthesis of enantio-enriched C₁ and C₂ symmetric BINOLs with the 3 and 3` positions available for further chemical modifications. On the basis of kinetic and racemization studies, we postulated the coupling of 2-naphthol involves an intermolecular oxidative radical-anion coupling by iron bisphosphate complex.

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