Chiral-at-Metal Rh(III) Complex Catalyzed Asymmetric Conjugate Addition of Unactivated Alkenes with α,β-Unsaturated 2-Acyl Imidazoles

Abstract

A newly prepared chiral-at-metal Rh(III) complex catalyzed highly efficient asymmetric conjugate addition of para-vinylanilines with α,β-unsaturated 2-acyl imidazoles is developed, affording the corresponding adducts in 67-95% yields with 86-95% ee. Remarkably, employing as low as 0.05 mol % of Rh(III) complex as catalyst, a gram-scale reaction still affords the desired product in 81% yield with 92% ee.

Acyl‐Imidazoles: A Privileged Ester Surrogate for Enantioselective Synthesis

“…Kang and co-workers recently reported a relevant enantioselective conjugate addition of 1,1'-diarylethene 50 to various α,β-unsaturated 2-acyl-imidazoles 1 catalyzed by a chiral-at-metal Rh(III) complex (Λ-RhO2) (Scheme 26). [36] The corresponding 1,4-adducts 51 were isolated in good yields and selectivities. It is noteworthy that a gramscale reaction involving a catalyst loading as low as 0.05 mol% was performed with a similar efficiency.…”

“…Simple alkenes have been more scarcely investigated due to their poor reactivity and uncontrolled side reactions. Kang and co‐workers recently reported a relevant enantioselective conjugate addition of 1,1′‐diarylethene 50 to various α,β‐unsaturated 2‐acyl‐imidazoles 1 catalyzed by a chiral‐at‐metal Rh(III) complex (Λ‐ RhO2 ) (Scheme ) . The corresponding 1,4‐adducts 51 were isolated in good yields and selectivities.…”

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

“…Therefore, the development of new chiral‐at‐metal complexes that match vinylogous Michael addition would be desired. Based on our previous success in designing and exploiting chiral rhodium catalysts, here a newly developed chiral‐at‐metal Rh(III) complex catalyzed enantioselective vinylogous Michael addition of α , α ‐dicyanoolefins with α , β ‐unsaturated carbonyl compounds has been realized (Scheme ), a variety of γ ‐substituted dicyanoolefin derivatives were obtained in high yields and enantioselectivities.…”

Cross-Dimerization of 2,5-Dihydrofuran with Conjugated Dienes Catalyzed by (Chiral Diene)ruthenium(0) Complexes and Origins of the Enantioselectivity

“…However, the scope and the enantioselectivity were limited. Afterword, Ho, Kang, and RajanBabu reported efficient catalytic systems for the enantioselective cross-dimerizations of substituted olefins (Scheme c–e). All these reactions are different from hydrovinylation and have been suggested to be either oxidative coupling mechanisms or hydride insertion mechanisms.…”