Preparation of Optically Pure Dinuclear Cobalt(III) Complex with Λ-Configuration as a Dianionic Chiral Catalyst

Abstract

The disodium salt of enantiomerically pure dimeric Λ-cobalt(III) complex 1 was prepared in one-pot from sodium triscarbonatocobaltate(III) and Schiff base ligand (Ra,S,S)-2 formed by the condensation of (R)-3,3ʹ-diformyl-2,2ʹ-dihydroxy-1,1ʹ-binaphthyl 3 with (S)-tert-leucine 4.Preliminary screening of 1 as a chiral catalyst was conducted for the bromocyclization of a tryptamine derivative.Enzymes often show high chemo-, regio-, and stereoselectivities that are difficult to achieve even with the latest organic synthetic methods. 1 In an enzyme-catalyzed process, two or more reaction-promoting units in the active site increase the reaction rate by their synergistic cooperation, leading to efficient product formation. 2 Inspired by the enzymatic activation of substrates, many researchers have attempted the development of catalysts mimicking their characteristic functionalities, toward the preparation of optically enriched chemicals. 3 Chiral hetero-and homo-bimetallic catalysts such as lanthanum-lithium-tris(binaphthoxide) (LLB), 4 aluminum-lithium-bis(binaphthoxide) (ALB), 4 and dinuclear vanadium complexes 5 are representative examples in this regard. In 1977, Belokon first introduced a series of chiral octahedral cobalt(III) complexes with a rigid framework and a unique chiral environment (Λ and Δ configurations of a metal center). 6 These anionic cobalt complexes are easily prepared through the self-assembly of sodium triscarbonatocobaltate(III) and Schiff base ligands derived

Synthesis and Structural and Optical Behavior of Dehydrohelicene-Containing Polycyclic Compounds

“…This protocol presents a highly efficient method for accessing diverse hetero [7]dehydrohelicenes 56 under mild conditions. The green electrochemical process sets itself apart by entirely eliminating metal waste, a notable departure from syntheses catalyzed by transitional metals [77][78][79][80][81][82]. The authors extended their approach to demonstrate the first enantioselective scalable synthesis of these dehydrohelicene molecules.…”

“…Sequential electrochemical synthesis of oxaza [7]dehydrohelicene: (upper) electrochemical one-pot process; (lower) stepwise enantioselective synthesis via chiral vanadium-catalyzed hetero-coupling and electrochemical oxidative transformations. by entirely eliminating metal waste, a notable departure from syntheses catalyzed by transitional metals [77][78][79][80][81][82]. The authors extended their approach to demonstrate the first enantioselective scalable synthesis of these dehydrohelicene molecules.…”