Cinchona-Based Hydrogen-Bond Donor Organocatalyst Metal Complexes: Asymmetric Catalysis and Structure Determination

In this study, we describe the synthesis of cinchona (thio)squaramide and a novel cinchona thiourea organocatalyst. These catalysts were employed in pharmaceutically relevant catalytic asymmetric reactions, such as Michael, Friedel-Crafts, and A3 coupling reactions, in combination with Ag(I), Cu(II), and Ni(II) salts. We identified several organocatalyst-metal salt combinations that led to a significant increase in both yield and enantioselectivity. To gain insight into the active catalyst species, we prepared organocatalyst-metal complexes and characterized them using HRMS, NMR spectroscopy, and quantum chemical calculations (B3LYP-D4/def2-TZVP), which allowed us to establish a structure-activity relationship.

Catalytic asymmetric Friedel-Crafts alkylation of unprotected indoles with nitroalkenes using a novel chiral Yb(OTf)3-pybox complex

Chiral chloro-indeno pybox has served as a new ligand for the Yb(OTf)3-catalyzed asymmetric Friedel-Crafts alkylation reaction of indoles with nitroalkenes. The tunable nature of pybox ligands enables the rational design of catalysts for optimal performance in terms of both activity and stereoselectivity in a Friedel-Crafts-type reaction. Good to excellent yields and enantioselectivities were obtained for a relatively wide range of substrates, including sterically hindered compounds, under optimized reaction conditions.

KOtBu-promoted Michael/aldol/ring-opening cascade reaction of cyclobutanones with chalcones

An efficient Michael/aldol/ring-opening cascade reaction of cyclobutanones with chalcones has been developed. This protocol employs inexpensive potassium tert-butoxide (KOtBu) as a promoter and enables an efficient synthesis of densely substituted cyclohex-3-ene-carboxylic acids in high yields with high diastereoselectivities, which are difficult to prepare through conventional approaches. The significant advantages of this methodology include transition-metal-free conditions, readily available starting materials, wide scope and high atom economy.

Nickel-Catalyzed Cascade Reaction of 2-Vinylanilines with gem-Dichloroalkenes

An efficient nickel-catalyzed cascade reaction of 2-vinylanilines with gem-dichloroalkenes has been developed to deliver diversely substituted quinolines in good to high yields. This protocol enables effective access to quinolines bearing various functional groups in the cascade process from readily available feedstock chemicals. Mechanistic studies suggest that two plausible pathways are involved in the IPr-nickel catalytic system.

Asymmetric [3 + 3] Annulation to Construct Trifluoromethylated Pyrazolo[3,4-b]pyridin-6-ones via Chiral Phosphoric Acid and MgSO4 Synergistic Catalysis

We developed a novel asymmetric Friedel-Crafts alkylation/transamidation tandem reaction for the enantio- and diastereoselective synthesis of pyrazolo[3,4-b]pyridin-6-ones bearing a -CF₃ unit via synergistic chiral phosphoric acid and MgSO₄ catalysis. This [3 + 3] annulation protocol allows the formation of trifluoromethylated pyrazolo[3,4-b]pyridin-6-ones with two adjacent tertiary stereocenters in moderate to high yields (up to 90%), enantioselectivities (up to 97% ee), and diastereoselectivities (up to >20:1 dr).

Zinc-catalyzed asymmetric [3 + 2] annulations for construction of chiral spiro[1-indanone-γ-butyrolactones] via a C−N bond cleavage process

An intriguing tandem Michael/lactonization reaction of α-hydroxy-1-indanones and methyleneindolinones has been established in this work. The employ of chiral dinuclear zinc catalysts is essential in achieving highly efficient chirality transfer...

Recent Advances in Selected Asymmetric Reactions Promoted by Chiral Catalysts: Cyclopropanations, Friedel–Crafts, Mannich, Michael and Other Zinc-Mediated Processes—An Update

The main purpose of this review article is to present selected asymmetric synthesis reactions in which chemical and stereochemical outcomes are dependent on the use of an appropriate chiral catalyst. Optically pure or enantiomerically enriched products of such transformations may find further applications in various fields. Among an extremely wide variety of asymmetric reactions catalyzed by chiral systems, we are interested in: asymmetric cyclopropanation, Friedel–Crafts reaction, Mannich and Michael reaction, and other stereoselective processes conducted in the presence of zinc ions. This paper describes the achievements of the above-mentioned asymmetric transformations in the last three years. The choice of reactions is related to the research that has been carried out in our laboratory for many years.

Regiodivergent Organocatalytic Reactions

Organocatalysts are abundantly used for various transformations, particularly to obtain highly enantio- and diastereomeric pure products by controlling the stereochemistry. These applications of organocatalysts have been the topic of several reviews. Organocatalysts have emerged as one of the very essential areas of research due to their mild reaction conditions, cost-effective nature, non-toxicity, and environmentally benign approach that obviates the need for transition metal catalysts and other toxic reagents. Various types of organocatalysts including amine catalysts, Brønsted acids, and Lewis bases such as N-heterocyclic carbene (NHC) catalysts, cinchona alkaloids, 4-dimethylaminopyridine (DMAP), and hydrogen bond-donating catalysts, have gained renewed interest because of their regioselectivity. In this review, we present recent advances in regiodivergent reactions that are governed by organocatalysts. Additionally, we briefly discuss the reaction pathways of achieving regiodivergent products by changes in conditions such as solvents, additives, or the temperature.