A Chiral Iron Disulfonate Catalyst for the Enantioselective Synthesis of 2-Amino-2′-hydroxy-1,1′-binaphthyls (NOBINs)

Abstract

A novel type of chiral redox disulfonate iron complex for asymmetric catalysis is reported. The [Fe((R a )-BINSate)] + (BINSate = 1,1′binaphthalene-2,2′-disulfonate) complex effectively promotes the enantioselective oxidative cross-coupling between 2-naphthols (1) and 2-aminonaphthalene derivatives (2), affording optically enriched (R a )-2-amino-2′hydroxy-1,1′-binaphthyls (NOBINs) with exceptional yields and enantioselective ratios (up to 99% yield and 96:4 er). The [Fe((R a )-BINSate)] + catalyst was designed as a chiral version of FeCl 3 with multicoordination sites available for binding the two coupling partners 1 and 2 as well as the oxidant. Our structure−selectivity and activity study, which covered most of the important positions in the NOBIN scaffold, revealed the effect of different substitution patterns on the coupling efficiency and stereoselectivity.

Catalytic Oxidative Coupling of Phenols and Related Compounds

“…While there has been much progress in achieving catalytic enantioselective oxidative coupling of naphthols and polycyclic phenols through Cu, Ru, V, and Fe catalysts in the past 30 years, − oxidative asymmetric phenol coupling reactions remain underdeveloped. Compared to naphthol oxidative coupling reactions, phenol oxidative coupling reactions are much harder to initiate and control due to the multiple resonance forms that contribute to the reactivity of oxidized phenol intermediates.…”

“…Compared to asymmetric naphthol oxidative coupling reactions, − there are fewer protocols for asymmetric phenol oxidative coupling reactions. To fill in this gap, we developed a monomeric asymmetric vanadium catalyst to achieve enantioselective oxidative coupling of phenol substrates.…”

Conformational enantiodiscrimination for asymmetric construction of atropisomers

“…1b ) are among the most prominent and valuable axially chiral molecules 17 – 24 . Enantiopure ( R )- and ( S )-BINOL and some of their derivatives are commercially available nowadays, in contrast, enantiopure BINAMs and NOBINs with diverse substitution patterns are still very difficult to obtain despite the fact that great efforts have been devoted to their synthesis in the past three decades 22 – 43 .…”

Pd‐catalyzed Aerobic Cross‐Dehydrogenative Coupling of Catechols with 2‐Oxindoles and Benzofuranones: Reactivity Difference Between Monomer and Dimer

“…The anion−radical mechanism helps us to understand the observed cross‐coupling selectivity in a generic way, with only minor modification in interpretation, even if the bond‐forming event takes place in the inner‐ or outer‐sphere of the metal complex. To date, versatile synthetic methods have been reported for the radical‐based cross‐dehydrogenative coupling (CDC) [5] reaction of phenols, including transition metal catalysis,[ 1c , 1e , 6 , 7 , 8 , 9 ] oxidant tuning,[ 5d , 10 , 11 ] photoredox catalysis, [12] and electrosynthesis. [13] Recently, Pappo, [14] Kozlowski, [15] and Uchida [16] independently reported catalyst‐controlled methods for the CDC reaction with two‐distinct phenols having very similar electronic properties for both E ox and N , expanding the substrate‐dependent limitation of the anion−radical coupling.…”