Catalytic highly enantioselective transfer hydrogenation of β-trifluoromethyl nitroalkenes. An easy and general entry to optically active β-trifluoromethyl amines

Metal-Organic Frameworks-Based Frustrated Lewis Pairs for Selective Reduction of Nitroolefins to Nitroalkanes

Nitroalkanes serve as essential intermediates in the synthesis of pharmaceuticals, agrochemicals, and functional materials. To date, nitroalkanes are mainly prepared from homogeneous catalysts such as noble transition metal catalysts with poor recyclability. Herein, we propose a metal-organic framework-frustrated Lewis pair (MOF-FLP) heterogeneous catalyst for selectively reducing nitroolefins to nitroalkanes under moderate reaction conditions. MOF enrichment effect can significantly improve the catalytic efficiency compared to homogeneous FLP catalysts. Benefiting from the strong interaction between FLP and MOF, the MOF-FLP catalyst exhibits outstanding recyclability. This work not only provides a convenient route for nitroalkane synthesis but also showcases the potential of porous heterogeneous FLP catalysts, offering inspiration for future catalytic design strategies.

Two-step synthesis of vicinal trifluoromethyl primary amines from α-(trifluoromethyl)styrenes and phthalimide

A novel two-step synthesis of β-trifluoromethyl primary amines from readily available α-(trifluoromethyl)styrenes and phthalimide is developed. The first step involves a hydroamination between α-(trifluoromethyl)styrenes and phthalimide (PhthNH) with the assistance of a base. Next, the hydrazinolysis of the resulting N-(β-trifluoromethyl-β-arylethyl)phthalimides with hydrazine hydrate affords the desired N-(β-trifluoromethyl-β-arylethyl)amines.

Generality-Driven Catalyst Development: A Universal Catalyst for Enantioselective Nitroalkene Reduction

Cracking the selectivity-generality paradox is among the most pressing challenges in asymmetric catalysis. This obstacle prevents the immediate and successful translation of new methods to diverse small molecules. This is particularly rate-limiting for therapeutic development, where availability and structural diversity are often critical components of successful campaigns. Here we describe the union of generality-driven enantioselective catalysis and the preparation of diverse peptidomimetics. A single new organocatalyst provides high selectivity and substrate generality that is matched only by a combination of metal and organocatalysts. Within organocatalysis, this discovery breaks a 16-year monolithic paradigm, uncovering a powerful new scaffold for enantioselective reduction with behavior that suggests the recognition of a nitroethylene minimal catalaphile.

Catalytic Asymmetric Conjugate Reduction

Enantioselective reduction reactions are privileged transformations for the construction of trisubstituted stereogenic centers. While these include established synthetic strategies, such as asymmetric hydrogenation, methods based on the enantioselective addition of hydridic reagents to electrophilic prochiral substrates have also gained importance. In this context, the asymmetric conjugate reduction (ACR) of α,β-unsaturated compounds has become a convenient approach for the synthesis of chiral compounds with trisubstituted stereocenters in α-, β-, or γ-position to electron-withdrawing functional groups. Because such activating groups are diverse and amenable of further derivatizations, ACRs provide a general and powerful synthetic entry towards a variety of valuable chiral building blocks. This Review provides a comprehensive collection of catalytic ACR methods involving transition-metal, organic, and enzymatic catalysis since its first versions dating back to the late 1970s.

DBN-Mediated Addition Reaction of α-(Trifluoromethyl)styrenes with Diazoles, Triazoles, Tetrazoles, and Primary, Secondary, and Secondary Cyclic Amines

A mild and efficient DBN-mediated addition reaction of α-(trifluoromethyl)styrenes with diazoles, triazoles, tetrazoles, and primary, secondary, and secondary cyclic amines was developed. This practical protocol provided a robust method for the synthesis of various β-trifluoromethyl nitrogen-containing heterocycles and β-trifluoromethyl amines.

Stereodivergent entry to β-branched β-trifluoromethyl α-amino acid derivatives by sequential catalytic asymmetric reactions

Currently, conventional reductive catalytic methodologies do not guarantee general access to enantioenriched β-branched β-trifluoromethyl α-amino acid derivatives. Herein, a one-pot approach to these important α-amino acids, grounded on the reduction - ring opening of Erlenmeyer-Plöchl azlactones, is presented. The configurations of the two chirality centers of the products are established during each of the two catalytic steps, enabling a stereodivergent process.

Enantioselective Iridium-Catalyzed Allylation of Nitroalkanes: Entry to β-Stereogenic α-Quaternary Primary Amines

The first systematic study of simple nitronate nucleophiles in iridium-catalyzed allylic alkylation is described. Using a tol-BINAP-modified π-allyliridium C,O-benzoate catalyst, α,α-disubstituted nitronates substitute racemic branched alkyl-substituted allylic acetates, thus providing entry to β-stereogenic α-quaternary primary amines. DFT calculations reveal early transition states that render the reaction less sensitive to steric effects and distinct trans-effects of diastereomeric chiral-at-iridium π-allyl complexes that facilitate formation of congested tertiary-quaternary C-C bonds.

Connecting and Analyzing Enantioselective Bifunctional Hydrogen Bond Donor Catalysis Using Data Science Tools

The generalization of related asymmetric processes in organocatalyzed reactions is an ongoing challenge due to subtle, noncovalent interactions that drive selectivity. The lack of transferability is often met with a largely empirical approach to optimizing catalyst structure and reaction conditions. This has led to the development of diverse structural catalyst motifs and inspired unique design principles in this field. Bifunctional hydrogen bond donor (HBD) catalysis exemplifies this in which a broad collection of enantioselective transformations has been successfully developed. Herein, we describe the use of data science methods to connect catalyst and substrate structural features of an array of reported enantioselective bifunctional HBD catalysis through an iterative statistical modeling process. The computational parameters used to build the correlations are mechanism-specific based on the proposed transition states, which allows for analysis into the noncovalent interactions responsible for asymmetric induction. The resulting statistical models also allow for extrapolation to out-of-sample examples to provide a prediction platform that can be used for future applications of bifunctional hydrogen bond donor catalysis. Finally, this multireaction workflow presents an opportunity to build statistical models unifying various modes of activation relevant to asymmetric organocatalysis.

Copper-Catalyzed Enantioselective Formation of C-CF3 Centers from β-CF3 -Substituted Acrylates and Acrylonitriles

The catalytic asymmetric synthesis of β-trifluoromethylated esters or nitriles is reported. The use of an in situ formed chiral Cu-H complex allowed the enantioselective reduction of β-trifluoromethylated acrylates or acrylonitriles. The reaction proceeds smoothly affording the corresponding enantioenriched products in good to excellent yields and outstanding enantioselectivities (up to 98 % ee). The mechanism of the reaction was studied, and a plausible reaction pathway was suggested accordingly. Finally, the versatility of the products was highlighted through functional group manipulations.

Rhodium-catalyzed asymmetric hydrogenation of β-branched enamides for the synthesis of β-stereogenic amines

β-Branched simple enamides were hydrogenated to give β-stereogenic amines in quantitative yields and with excellent enantioselectivities.

Recent advances in organocatalytic enantioselective transfer hydrogenation

Robust, environmentally friendly reductants enable highly enantioselective reactions in the presence of chiral catalysts.

A General Catalytic Enantioselective Transfer Hydrogenation Reaction of β,β-Disubstituted Nitroalkenes Promoted by a Simple Organocatalyst

Given its synthetic relevance, the catalytic enantioselective reduction of β,β-disubstituted nitroalkenes has received a great deal of attention. Several bio-, metal-, and organo-catalytic methods have been developed, which however are usually applicable to single classes of nitroalkene substrates. In this paper, we present an account of our previous work on this transformation, which implemented with new disclosures and mechanistic insights results in a very general protocol for nitroalkene reductions. The proposed methodology is characterized by (i) a remarkably broad scope encompassing various nitroalkene classes; (ii) Hantzsch esters as convenient (on a preparative scale) hydrogen surrogates; (iii) a simple and commercially available thiourea as catalyst; (iv) user-friendly procedures. Overall, the proposed protocol gives a practical dimension to the catalytic enantioselective reduction of β,β-disubstituted nitroalkenes, offering a useful and general platform for the preparation of nitroalkanes bearing a stereogenic center at the β-position in a highly enantioenriched form. A transition state model derived from control kinetic experiments combined with literature data is proposed and discussed. This model accounts and justifies the observed experimental results.

Metal-Templated Design: Enantioselective Hydrogen-Bond-Driven Catalysis Requiring Only Parts-per-Million Catalyst Loading

Based on a metal-templated approach using a rigid and globular structural scaffold in the form of a bis-cyclometalated octahedral iridium complex, an exceptionally active hydrogen-bond-mediated asymmetric catalyst was developed and its mode of action investigated by crystallography, NMR, computation, kinetic experiments, comparison with a rhodium congener, and reactions in the presence of competing H-bond donors and acceptors. Relying exclusively on weak forces, the enantioselective conjugate reduction of nitroalkenes can be executed at catalyst loadings as low as 0.004 mol% (40 ppm), representing turnover numbers of up to 20 250. A rate acceleration by the catalyst of 2.5 × 10(5) was determined. The origin of the catalysis is traced to an effective stabilization of developing charges in the transition state by carefully orchestrated hydrogen-bonding and van der Waals interactions between catalyst and substrates. This study demonstrates that the proficiency of asymmetric catalysis merely driven by hydrogen-bonding and van der Waals interactions can rival traditional activation through direct transition metal coordination of the substrate.

Reversible modulation of the activity of thiourea catalysts with anions: a simple approach to switchable asymmetric catalysis

A simple and straightforward approach to switchable asymmetric catalysis is presented, based on the interactions of thiourea catalysts with anions.