Reported here is a highly enantioselective homoenolate Michael addition/esterification sequence of cyclohexadienone-tethered enals via N-heterocyclic carbene (NHC) catalysis, affording the enantiopure -hydrobenzofurans, -hydroindoles, and -hydroindenes. The NHC catalyst bearing a nitro group greatly enhances the stereocontrol, and a bulky -aryl substituent of the triazolium salt in the catalyst is helpful for inhibiting the further aldol condensation after homoenolate Michael addition. The utility of this protocol is highlighted by a gram-scale experiment and versatile downstream transformations.
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A Highly Enantioselective Homoenolate Michael Addition/Esterification Sequence of Cyclohexadienone-Tethered Enals via NHC Catalysis.
Org Lett
February 2023
The Research Center of Chiral Drugs, Shanghai Frontiers Science Center for TCM Chemical Biology, Innovation Research Institute of Traditional Chinese Medicine, Shanghai University of Traditional Chinese Medicine, 1200 Cailun Road, Shanghai 201203, China.
Reported here is a highly enantioselective homoenolate Michael addition/esterification sequence of cyclohexadienone-tethered enals via N-heterocyclic carbene (NHC) catalysis, affording the enantiopure -hydrobenzofurans, -hydroindoles, and -hydroindenes. The NHC catalyst bearing a nitro group greatly enhances the stereocontrol, and a bulky -aryl substituent of the triazolium salt in the catalyst is helpful for inhibiting the further aldol condensation after homoenolate Michael addition. The utility of this protocol is highlighted by a gram-scale experiment and versatile downstream transformations.
View Article and Find Full Text PDFDearomative Michael addition involving enals and 2-nitrobenzofurans realized under NHC-catalysis.
Chem Commun (Camb)
April 2022
Institute of Organic Chemistry, Faculty of Chemistry, Lodz University of Technology, Żeromskiego 116, 90-924 Łódź, Poland.
In this manuscript, the first enantioselective dearomative Michael addition between α,β-unsaturated aldehydes and 2-nitrobenzofurans realized under N-heterocyclic carbene activation has been described. The reaction proceeds addition of homoenolate to Michael acceptors leading to the formation of biologically important heterocycles with high yields and stereoselectivities. Their functionalization potential has been confirmed in selected, diastereoselective transformations.
View Article and Find Full Text PDFSynthesis of Functionalized Dihydrocoumarins by NHC-Catalyzed [3 + 3] Annulation of Enals with 2-Substituted Naphthoquinones.
Org Lett
October 2021
Department of Organic Chemistry, Indian Institute of Science, Bangalore-560012, India.
The [3 + 3] annulation of α,β-unsaturated aldehydes with 2-substituted 1,4-naphthoquinones allowing the facile synthesis of functionalized dihydrocoumarins catalyzed by N-heterocyclic carbene (NHC) is reported. The initially formed NHC-homoenolates underwent an efficient Michael-isomerization-lactonization cascade to furnish the products. Preliminary studies on mechanism shed light on the homoenolate pathway over the intermediacy of the α,β-unsaturated acylazolium intermediates.
View Article and Find Full Text PDFUnveiling the Chemo- and Stereoselectivities of NHC-Catalyzed Reactions of an Aliphatic Ester with Aminochalcone.
J Org Chem
July 2020
College of Chemistry, Zhengzhou University, 100 Science Avenue, Zhengzhou, Henan 450001, P. R. China.
The possible mechanisms and origin of selectivities in N-heterocyclic carbene (NHC)-catalyzed reactions of an aliphatic ester with aminochalcone were studied using density functional theory. Herein, a general mechanistic map involving various types of possible intermediates was discovered, and the corresponding chemoselective pathways were systematically investigated. Based on the computational results, the most energetically favorable reaction pathway mainly involved in the following processes: formation of a homoenolate intermediate via α/β-H elimination, formal Michael addition of a homoenolate intermediate to aminochalcone, intramolecular aldol-type reaction, and ring closure to form the lactam product.
View Article and Find Full Text PDFBifunctional N-Heterocyclic Carbenes Derived from l-Pyroglutamic Acid and Their Applications in Enantioselective Organocatalysis.
Acc Chem Res
March 2020
Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Molecular Recognition and Function, CAS Research/Education Center for Excellence in Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, 100190 Beijing, China.
In nature, enzymes are a powerful medium for the construction of enantiomerically pure chemicals, which always inspires synthetic chemists to explore new catalysts to imitate the enzyme machinery for asymmetric transformations. Vitamin B1, a bifunctional thiazolium N-heterocyclic carbene (NHC) precursor, is the coenzyme for transketolase. In the past two decades, a series of chiral NHCs, including monocyclic, bicyclic, tetracyclic, and even bridged ones, have been synthesized and successfully utilized as efficient organocatalysts for a wide variety of asymmetric organic reactions.
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