Reaction-Based Mechanistic Investigations of Asymmetric Hetero-Diels-Alder Reactions of Enones with Isatins Catalyzed by Amine-Based Three-Component Catalyst Systems

1,3-Diamine-Derived Catalysts: Design, Synthesis, and the Use in Enantioselective Mannich Reactions of Ketones

1,3-Diamine-derived catalysts were designed, synthesized, and used in asymmetric Mannich reactions of ketones. The reactions catalyzed by one of the 1,3-diamine derivatives in the presence of acids afforded the Mannich products with high enantioselectivities under mild conditions. In most cases, bond formation occurred at the less-substituted α-position of the ketone carbonyl group. Our results indicate that the primary and the tertiary amines of the 1,3-diamine derivative cooperatively act for the catalysis.

Amines as Catalysts: Dynamic Features and Kinetic Control of Catalytic Asymmetric Chemical Transformations to Form C-C Bonds and Complex Molecules

Carbonyl transformations involving enolates and/or enamines have been used for various types of bond-forming reactions. In this account, catalysts and catalyst systems that have amino acids or primary, secondary, and/or tertiary amines as key catalytic functional groups that we have developed to accelerate chemical transformations, including regio-, diastereo- and enantioselective reactions, are discussed. Our chemical transformation strategies and methods that use amine derivatives as catalysts are also discussed. As amines can have different functions depending on protonation and on the species formed during the catalysis (such as enamines and iminium ions), dynamics and kinetic controls are the keys for understanding the catalysis. Further, strategies that harness dynamic steps and kinetic control in amine-catalyzed reactions have enabled the synthesis of complex molecules in stereocontrolled manners. Understanding the dynamic features and the kinetic controls of the catalysis will further the design of the catalysts and the development of chemical transformation strategies and methods.

Organocatalytic diastereo- and enantioselective oxa-hetero-Diels-Alder reactions of enones with aryl trifluoromethyl ketones for the synthesis of trifluoromethyl-substituted tetrahydropyrans

Tetrahydropyran derivatives are found in bioactives, and introduction of the trifluoromethyl group into molecules often improves biofunctions. Here we report diastereo- and enantioselective oxa-hetero-Diels-Alder reactions catalyzed by amine-based catalyst systems that afford trifluoromethyl-substituted tetrahydropyranones. Catalyst systems and conditions suitable for the reactions to provide the desired diastereomer products with high enantioselectivities were identified, and various trifluoromethyl-substituted tetrahydropyranones were synthesized with high diastereo- and enantioselectivities. Mechanistic investigation suggested that the reactions involve a [4 + 2] cycloaddition pathway, in which the enamine of the enone acts as the diene and the ketone carbonyl group of the aryl trifluoromethyl ketone acts as the dienophile. In this study, tetrahydropyran derivatives with the desired stereochemistry that are difficult to synthesize by previously reported methods were concisely obtained, and the range of tetrahydropyran derivatives that can be synthesized was expanded.

Intramolecular Formal [4 + 2] Cycloadditions: Synthesis of Spiro Isoindolinone Derivatives and Related Molecules

Acid-catalyzed intramolecular reactions of isoindolinone-derived hydroxylactam derivatives bearing enones or enals that afford spiro isoindolinone derivatives and related molecules have been developed. From the hydroxylactam moieties, N-acylenamides were generated in situ and reacted with the enone and the enal moieties via formal [4 + 2] cycloaddition reactions to construct cyclohexanone- and dihydropyran-fused ring systems and the spiro ring systems.

Box-copper catalyzed asymmetric inverse-electron-demand oxa-hetero-Diels–Alder reaction for efficient synthesis of spiro pyranyl-oxindole derivatives

A chiral Box/Cu catalyzed asymmetric IEDDA reaction between isatin-derived β,γ-unsaturated α-ketoesters and electron-rich olefins was developed, which provided chiral spiro oxindole-pyrans in excellent yields with excellent stereoselectivities.

Simple primary β-amino alcohols as organocatalysts for the asymmetric Michael addition of β-keto esters to nitroalkenes

Simple primary β-amino alcohols act as an efficient organocatalysts in the asymmetric Michael addition of β-keto esters with nitroalkenes affording highly pure chiral Michael adducts. Also, both enantiomers of the adducts were obtained, depending on the specific catalyst used and reaction temperature.

Simple organocatalyst component system for asymmetric hetero Diels-Alder reaction of isatins with enones

A simple two catalyst component system consisting of primary β-amino alcohols as a catalyst and amino acids as a co-catalyst put together works as an efficient organocatalyst system in the hetero Diels-Alder reaction of isatins with enones to afford the chiral spirooxindole-tetrahydropyranones in good chemical yields and stereoselectivities (up to 86%, up to 85 : 15 dr., up to 95% ee).

Chiral Thioureas-Preparation and Significance in Asymmetric Synthesis and Medicinal Chemistry

For almost 20 years, thioureas have been experiencing a renaissance of interest with the emerged development of asymmetric organocatalysts. Due to their relatively high acidity and strong hydrogen bond donor capability, they differ significantly from ureas and offer, appropriately modified, great potential as organocatalysts, chelators, drug candidates, etc. The review focuses on the family of chiral thioureas, presenting an overview of the current state of knowledge on their synthesis and selected applications in stereoselective synthesis and drug development.

Mannich Reactions of Carbohydrate Derivatives with Ketones To Afford Polyoxy-Functionalized Piperidines

Mannich reactions of carbohydrate derivatives with ketones that afford polyoxy-functionalized piperidines are reported. Ketone nucleophiles (enamines/enolates) were generated in the presence of the amines used for the formation of the iminium ions of sugar derivatives with or without an additive. Conditions to preferentially generate piperidine derivatives rather than tetrahydrofurans were identified. Products from the reactions of allyl ketones were readily transformed to bicyclic piperidines.

Enantioselective Hetero-Diels-Alder Reaction and the Synthesis of Spiropyrrolidone Derivatives

An efficient enantioselective hetero-Diels-Alder reaction was developed under catalysis of a chiral copper complex. A variety of spiropyrrolidones, which bear a tetra-substituted carbon stereocenter, can be obtained in good yields with excellent enantioselectivities by virtue of this method. Furthermore, a substrate-dependent reaction pathway was proposed on the basis of the isolated intermediates.

Catalytic asymmetric synthesis of spirooxindoles: recent developments

The past four years have witnessed significant developments in the field of the catalytic asymmetric synthesis of spirooxindoles, and this feature article outlines the recent progress in this area, including the contributions of our group. This article is divided into sections according to the size and type of the generated spiro-ring fused at the C3-position of the oxindole core.

Thermal Hetero-Diels-Alder Reaction of Benzocyclobutenones with Isatins To Form 2-Oxindole Spirolactones

Benzocyclobutenones 1a-1g undergo cycloreversion at 150 °C in m-xylene solvent to form transient α-oxo-ortho-quinodimethanes or "ortho-quinoid ketene methides", which engage in intermolecular [4+2] cycloadditions with isatins 2a-2f to form 2-oxindole spirolactones 3a-3l. This process tolerates an array of different functional groups and substitution patterns, and is applicable to unprotected isatins 2b-2f bearing free NH-functionalities. The superior performance of isatins compared to other carbonyl based dienophiles was demonstrated and rationalized with the aid of quantum chemical calculations.

Discovery of SOAT2 inhibitors from synthetic small molecules

Synthesis of new functionalized molecules and identification of biofunctional molecules can lead to the development of therapeutic leads and molecular tools for biomedical research. We have recently reported oxa-hetero-Diels-Alder reactions of enones with isatins to provide functionalized spirooxindole tetrahydropyran derivatives. Twenty-one compounds from the spirooxindole tetrahydropyran derivatives and related molecules were screened for inhibition of sterol O-acyltransferase (SOAT) isozymes SOAT1 and SOAT2. Three racemic derivatives inhibited the SOAT2 isozyme with three-fold or better selectivity for SOAT2 than for SOAT1. The enantiomerically enriched forms of the most efficient racemic inhibitor of SOAT2 were further evaluated; one enantiomer inhibited SOAT2 with an IC50 of 1.5μM and was 10-fold more selective for SOAT2 than SOAT1.

Catalytic enantioselective oxa-hetero-Diels–Alder reactions of enones with aryl trifluoromethyl ketones

Asymmetric oxa-hetero-Diels–Alder reactions of enones with aryl trifluoromethyl ketones were developed to afford tetrahydropyranones bearing trifluoromethyl-substituted tetrasubstituted carbon centers.

Catalytic asymmetric hetero-Diels–Alder reactions of enones with isatins to access functionalized spirooxindole tetrahydropyrans: scope, derivatization, and discovery of bioactives

Concise hetero-Diels–Alder reactions were developed to provide various functionalized spirooxindole tetrahydropyrans useful for the discovery of bioactive molecules.