Chiral‐at‐Metal Rhodium(III) Complex Catalyzed Enantioselective Vinylogous Michael Addition of α,α‐Dicyanoolefins with α,β‐Unsaturated 2‐Acyl Imidazoles

Abstract

As a development of traditional vinylogous Michael addition reactions, catalytic enantioselective γ‐functionalization of α,α‐dicyanoolefins possesses a remarkable advantage in carboxylic derivatives synthesis and has emerged as a powerful tool for the preparation of high value chemicals. In another hand, the development of versatile and highly efficient catalyst is quite critical for such asymmetric transformations. Herein, a newly developed chiral‐at‐metal rhodium (III) complex catalyzed enantioselective vinylogous Michael addition of α,α‐dicyanoolefins with α,β‐unsaturated 2‐acyl imidazoles has been realized, delivering the corresponding adducts in 68−89 % yields with up to 95 % enantioselectivity. The reaction can be conducted on a gram‐scale using a low catalyst loading (0.5 mol %) without impacting its efficiency.

Metal Stereogenicity in Asymmetric Transition Metal Catalysis

“…Scheme a displays that Λ- M66 at a loading of 0.2 mol % catalyzes the enantioselective α-amination of 2-acyl imidazole 101 with dibenzyl azodicarboxylate ( 104 ) to provide the α-amination product ( R )- 105 with 88% yield and 96% ee . Meggers, Gong, and particularly Kang and Du demonstrated the versatility of Λ- and Δ- M66 and its derivatives to serve as chiral Lewis acid catalysts for a large variety of reactions. − The related benzothiazole complexes Λ- and Δ- M67 , which are the lighter congeners of iridium-based Λ- and Δ- M65 and its derivatives, are for many applications even more powerful chiral Lewis acids providing typically higher enantioselectivities. − Importantly, compared to the related bis-cyclometalated iridium catalysts, the rhodium catalysts feature much higher ligand exchange rates by several orders of magnitude . This is a significant advantage because ligand exchange reaction (e.g., coordination of substrate and release of product) are often the rate limiting steps in a catalytic cycle and, thus, determine the overall turnover frequency.…”

Asymmetric Synthesis of Tertiary α-Hydroxylation-Cyclopentanones via Synergetic Catalysis of Chiral-at-Metal Rhodium(III) Complexes/Pyrrolidine

“…To the best of our knowledge, the catalytic asymmetric domino Michael/aldol reaction-initiated ring-closure reaction for the diastereo- and enantioselective construction of three contiguous stereocenters tertiary α-hydroxylation cyclic ketones with arylpropane-1,2-diones and α,β-unsaturated ketones has not been reported yet. As part of our ongoing interest in chiral-at-metal complexes developing a new synthetic methodology, , herein we report an enantioselective annulation reaction of arylpropane-1,2-diones with α,β-unsaturated 2-acyl imidazoles catalyzed by chiral-at-metal Rh (III) complexes or Ir (III) complexes.…”

Bipyridine-N,N′-dioxides Catalysts: Design, Synthesis, and Application in Asymmetric Synthesis of 1H-Pyrazolo[3,4-b]pyridine Analogues

“…Although the previous research has left a deep impression on us, not all existing ligands could meet every reaction, so the development of a novel type of highly efficient chiral C 2-symmetric N -dioxides catalyst was still needed. Inspired by previous research and combined with our experience in developing chiral-at-metal Rh­(III) complexes, herein we designed and synthesized a new tetradentate C 2-symmetric chiral bipyridine- N , N ′-dioxides ligand and successfully applied them to synthesize chiral pyrazolo­[3,4- b ]­pyridine analogues (Scheme ). …”