Enantio- and Diastereoselective Asymmetric Addition of 1,3-Dicarbonyl Compounds to Nitroalkenes in a Doubly Stereocontrolled Manner Catalyzed by Bifunctional Rosin-Derived Amine Thiourea Catalysts

Sparteine Thiourea: The Synthesis of an N Chiral Bispidine-Quinolizidine-Derived Organocatalyst and Applications in Asymmetric Synthesis of Dihydropyrano[c]chromenes

Bispidine, a bridged bicyclic diamine, has been widely utilized as a rigid scaffold in chiral chelating ligands in asymmetric synthesis. In particular, a chiral bispidine-quinolizidine hybrid, such as sparteine, was utilized in asymmetric synthesis involving a metal, exhibiting superior catalytic activity. In this study, we report the design and synthesis of a series of sparteine-derived organocatalysts and the utilization of these catalysts in tandem Michael addition-cyclization reactions. These catalysts have shown excellent catalytic reactivity and enantioselectivity, and the corresponding dihydropyrano[c]chromenes have been prepared in ≤99% yield and ≤99% ee with a low catalyst loading. The recycled catalysts maintain a good catalytic performance even after four cycles, and a gram-scale reaction with a 1% catalyst loading is also performed, providing the product in 96% yield and 98% ee.

Dehydroabietane-type bifunctional organocatalysts in asymmetric synthesis: recent progress

Dehydroabietane-type bifunctional organocatalysts derived from rosane-type diterpenes of dehydroabietic acid (DHAA) and dehydroabietylamine (DA) have been utilized in a wide variety of highly enantioselective reactions. Since one well-documented review exclusively reported on the development of terpene-derived bifunctional thioureas in asymmetric organocatalysis in 2013, fragmentary progress on the dehydroabietane-type bifunctional thioureas and squaramides has been mentioned in other reviews. In this mini-review, we systematically analyze and reorganize the published literature on dehydroabietane-type bifunctional organocatalysts in the recent decade according to the type of catalysts. Our aim is for this review to provide helpful research information and serve as a foundation for further design and application of rosin-based organocatalysts.

Crystallization-Enabled Stereoconvergent Michael Additions of β-Keto Esters to Nitroolefins

Asymmetric Michael additions are powerful tools to meet the growing need for stereochemically complex products. While 1,3-dicarbonyls are common nucleophiles, the successful use of configurationally unstable β-keto esters in diastereoselective variants remains understudied. In this Letter, crystalline β-keto esters were leveraged in a two-phase, one-pot merger of an asymmetric Michael addition with a crystallization-induced diastereomer transformation. Tuning the crystallinity of β-keto ester adducts enabled stereoconvergence of the products, which were isolated by filtration.

First synthesis of acylated nitrocyclopropanes

Although nitrocyclopropanedicarboxylic acid esters are widely used in organic syntheses, nitrocyclopropanes with an acyl group have not yet been synthesized. When adducts of β-nitrostyrene and 1,3-dicarbonyl compounds are treated with (diacetoxyiodo)benzene and tetrabutylammonium iodide, iodination occurs at the α-position of the nitro group, and the subsequent O-attack of the enol moiety leads to 2,3-dihydrofuran. Cyclopropane was successfully synthesized through C-attack as the acyl group became bulkier. The obtained nitrocyclopropane was transformed into furan upon treatment with tin(II) chloride via a ring-opening/ring-closure process.

Enantioselective organocatalytic Michael reactions using chiral (R,R)-1,2-diphenylethylenediamine-derived thioureas

Although the Michael addition is a very well-known and widely applied reaction, cost-effective, metal-free, and readily prepared organic catalysts remain rare. A chiral, bifunctional, (R,R)-1,2-diphenylethylenediamine-derived thiourea organic catalyst was developed and applied to asymmetric Michael additions of nitroalkenes under neutral conditions. Generally, fluorine-substituted thiourea catalysts exhibited high chemical yields and enantioselectivities under neutral conditions. The mild reactions were tolerant of many functional groups and afforded good-to-excellent yields, as well as high diastereo- and enantioselectivities for the Michael adducts. The utility of the transformation was demonstrated by the synthesis of a bioactive compound, (R)-Phenibut.

Organocatalytic Enantioselective Conjugate Addition of Nitromethane to Benzylidene-2-Benzoyl Acetate: Asymmetric Synthesis of ABT - 627, an Endothelin Receptor Antagonist

First catalytic and enantioselective conjugate addition of nitromethane to benzylidene-2-benzoyl acetate has been developed using dihydroquinine derived squaramide catalyst with moderate to high selectivities. Asymmetric total synthesis of ABT-627, a potent ETA receptor antagonist is accomplished utilizing the developed method in overall 15.7% yield.

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.

Catalytic 1,2-Rearrangements: Organocatalyzed Michael/Semi-Pinacol-like Rearrangement Cascade of 1,3-Diones and Nitroolefins

New types of organocatalytic 1,2-rearrangements, which resemble the Smiles-like or semi-pinacol-like rearrangement, of Michael adducts of 1,3-dicarbonyl-2-alkyl compounds and nitroalkenes have been realized. Unlike the well-known conjugate addition, the reaction affords the 1-phenyl-1-nitroalkanes via unprecedented rearrangement and cascade reactions. Structures of the appropriate products were unambiguously characterized by X-ray crystallography.

Asymmetric Michael Addition of Malononitrile with Chalcones via Rosin-Derived Bifunctional Squaramide

A rosin-derived bifunctional squaramide catalyzed asymmetric Michael addition of malononitrile with chalcones was discovered. This protocol provides a methodology for the facile synthesis of chiral γ-cyano carbonyl compounds in high yields and enantioselectivities (up to 99% yield and 90% ee) with a lower catalyst loading (0.3 mol%). The predominant R-configured adducts were obtained by this organocatalystic reaction, according to the experimental findings.

Advances in Rosin-Based Chemicals: The Latest Recipes, Applications and Future Trends

A comprehensive review of the publications about rosin-based chemicals has been compiled. Rosin, or colophony, is a natural, abundant, cheap and non-toxic raw material which can be easily modified to obtain numerous useful products, which makes it an excellent subject of innovative research, attracting growing interest in recent years. The last extensive review in this research area was published in 2008, so the current article contains the most promising, repeatable achievements in synthesis of rosin-derived chemicals, published in scientific literature from 2008 to 2018. The first part of the review includes low/medium molecule weight compounds: Especially intermediates, resins, monomers, curing agents, surfactants, medications and biocides. The second part is about macromolecules: mainly elastomers, polymers for biomedical applications, coatings, adhesives, surfactants, sorbents, organosilicons and polysaccharides. In conclusion, a critical evaluation of the publications in terms of data completeness has been carried out with an indication of the most promising directions of rosin-based chemicals development.

A homodinuclear cobalt complex for the catalytic asymmetric Michael reaction of β-ketoesters to nitroolefins

A homodinuclear Co₂/aminophenol sulfonamide complex has been developed for the asymmetric Michael reaction.

A dramatic synergistic effect of a flexible achiral linker on a rigid chiral cis-1,2-diamine bifunctional organocatalyst

The combination of a “rigid” chiral bicyclic cis-1,2-diamine skeleton and a “flexible” achiral linker was newly designed as a bifunctional organocatalyst framework and showed excellent catalytic activity, accompanied by the reversal of enantioselection.

Design and application of a bifunctional organocatalyst guided by electron density topological analyses

Design of a catalyst via the identification of key interactions within the transition state with quantum chemical topology.

Bifunctional Thioureas with α-Trifluoromethyl or Methyl Groups: Comparison of Catalytic Performance in Michael Additions

Thioureas are an important scaffold in organocatalysis because of their ability to form hydrogen bonds that activate substrates and fix them in a defined position, which allows a given reaction to occur. Structures that enhance the acidity of the thiourea are usually used to increase the hydrogen-bonding properties, such as 3,5-bis(trifluoromethyl)phenyl and boronate ureas. Herein, we report the synthesis of bifunctional thioureas with a chiral moiety that include either a trifluoromethyl or methyl group. Their catalytic performance in representative Michael addition reactions was used in an effort to compare the electronic effects of the fluorination at the methyl group. The observed differences concerning yields and ee values cannot be attributed solely to the different steric environments; theoretical results indicate distinct interactions within the corresponding transition states. The calculated transition states show that the fluorinated catalysts have stronger N-H···O and C-H···F hydrogen bonds, while the nonfluorinated systems have C-H···π contacts. These results have shown that a variety of hydrogen-bonding interactions are important in determining the yield and selectivity of thiourea organocatalysis. These details can be further exploited in catalyst design.

The squaramide-catalyzed asymmetric Michael/cyclization tandem reaction for the synthesis of chiral trifluoromethylated hydroxyimino tetrahydrobenzofuranones

An enantioselective synthesis of trifluoromethylated hydroxyimino tetrahydrobenzofuranones has been developed. 1,3-Dicarbonyl carbocyclic compounds react with β-CF3-β-disubstituted nitroalkenes in the presence of a chiral squaramide catalyst, providing efficient access to diverse hydroxyimino tetrahydrobenzofuranones featuring a trifluoromethyl group at the C3-position of an all-carbon quaternary stereocenter with good yields (up to 81%) and enantioselectivities (up to 89% ee).

Novel ferrocene-based bifunctional amine-thioureas for asymmetric Michael addition of acetylacetone to nitroolefins

An efficient method was developed to synthesize ferrocene-based bifunctional amine-thioureas bearing multiple hydrogen-bonding donors. Asymmetric Michael addition of acetylacetone to nitroolefins catalyzed by these novel bifunctional catalysts affords the Michael adducts in high yield and moderate to excellent enantioselectivities. Multiple hydrogen-bonds play an important role in accelerating the reaction.

Novel Chiral Bifunctional L-Thiazoline-Thiourea Derivatives: Design and Application in Enantioselective Michael Reactions

Several novel chiral bifunctional L-thiazoline-thiourea derivatives were easily synthesized from commercially available L-cysteine in high yield. These catalysts were subsequently applied to the enantioselective Michael addition of acetylacetone to β-nitrostyrenes. The products with S configuration were obtained in 98% enantiomeric excess (ee) when the L-thiazoline-thiourea derivatives were used. A plausible transition state model is proposed to explain the observed enantioselectivities.

One pot domino reaction accessing γ-nitroesters: synthesis of GABA derivatives

γ-Nitroesters are synthesized by the one pot domino process. GABA derivatives phenibut and baclofen were readily accessed.

Organocatalytic enantio- and diastereoselective conjugate addition to nitroolefins: when β-ketoamides surpass β-ketoesters

Our findings on the bifunctional squaramide-catalyzed enantioselective conjugate addition of β-ketoamides to nitroolefins are disclosed. It appears that simple acyclic methylene β-ketoamides, unlike the extensively studied β-ketoesters, afford the products in excellent diastereoselectivities, and maintain high yields and enantioselectivities. Moreover, competition and kinetic studies were conducted to rationalize the observed reactivity and selectivity. The high level of diastereocontrol, along with the amenability of the amide group to postfunctionalization, dramatically increase the synthetic usefulness of the transformation.

Ferrocene as a scaffold for effective bifunctional amine–thiourea organocatalysts

This work demonstrates that ferrocene could be an excellent scaffold for chiral organocatalysts.

Organocatalyzed asymmetric Michael reaction of β-aryl-α-ketophosphonates and nitroalkenes

The first enantioselective Michael reaction of β-aryl-α-ketophosphonates and nitroalkenes has been brealized by using a new bifunctional Takemoto-type thiourea catalyst. The primary Michael adducts obtained were converted in situ to the corresponding amides through the aminolysis. High yields, excellent diastereoselectivities (>95:5 dr), and good enantioselectivities (up to 81% ee) have been achieved for the corresponding α ,β-disubstituted γ-nitroamides. This reaction againdemon strated that α-ketophosphonates are interesting pronucleophiles that can be used as amide surrogates in organocatalyzed reactions.

Basic-functionalized recyclable ionic liquid catalyst: A solvent-free approach for Michael addition of 1,3-dicarbonyl compounds to nitroalkenes under ultrasound irradiation

A task-specific ionic liquid (TSIL) has been introduced as a recyclable catalyst in Michael addition. A series of nitroalkenes and various C-based nucleophiles were reacted in the presence of 30mol% of recyclable basic-functionalized ionic liquid. Good to excellent yields were obtained in 30min under ultrasound irradiation.

Cu-catalyzed selective mono-N-pyridylation: direct access to 2-aminoDMAP/sulfonamides as bifunctional organocatalysts

Direct and selective mono-N-pyridylation of trans-(R,R)-cyclohexane-1,2-diamine is described here. Facile preparation of a novel chiral 2-aminoDMAP core catalaphore via Cu catalysis has led to the development of various sulfonamide/2-aminoDMAPs as bifunctional acid/base organocatalysts (most in two steps overall), which have been shown to very effectively promote asymmetric conjugate addition of acetylacetone to trans-β-nitroolefins with good to excellent yields (87-93%) and enantioselectivites (up to 99%).

Observation of neighboring ortho-hydroxyl group participation in organocatalytic asymmetric sequential Michael-lactonization reactions: synthesis of highly substituted chiral spirodihydrocoumarins

A general approach to asymmetric synthesis of highly substituted spirodihydrocoumarins with a quaternary stereocenter was achieved through neighboring ortho-hydroxyl group induced sequential Michael-lactonization reactions on 2-(2-nitrovinyl)phenols with alkyl cyclopentanone-2-carboxylates in the presence of a catalytic amount of quinine-NH-thiourea followed by p-TSA.