A Chiral Primary Amine Thiourea Catalyst for the Highly Enantioselective Direct Conjugate Addition of α,α-Disubstituted Aldehydes to Nitroalkenes

Asymmetric Carbene Transformations for the Construction of All-Carbon Quaternary Centers

Asymmetric catalytic carbene reactions have been well documented in the last few decades for the expeditious assembly of chiral molecules with structural diversity. However, the enantioselective construction of all-carbon quaternary centers remains a challenge in this area. In this review article, two types of asymmetric carbene reactions that beyond cyclopropanation, cyclopropenation, and Büchner reaction, have been summarized for the construction of all-carbon quaternary centers: 1) using carbene species as a 1C synthon that reacts with a trisubstituted prochiral center; 2) sequential installation of two different C-C bonds on the carbene position, which features a gem-difunctionalization reaction. Especially, the asymmetric metal carbene gem-dialkylation process, which has emerged as a practical and versatile method for the expeditious assembly of complex architectures from readily available chemical resources, is a complementary approach for the expeditious assembly of all-carbon quaternary centers.

Enantioselective conjugate addition to nitroolefins catalysed by helical peptides with a single remote stereogenic centre

Two short pentapeptides rich in α-aminoisobutyric acid (Aib) residues have been shown to act as enantioselective organocatalysts for the conjugate addition of nucleophiles to nitroolefins. An L-alanine terminated peptide, (Aib)4(L-Ala)NHtBu, which has neither functionalised sidechains nor a highly designed reactive site, used an exposed N-terminal primary amine and the amide bonds of the backbone to mediate catalysis. Folding of this peptide into a 310 helical structure was observed by crystallography. Folding into a helix relays the conformational preference of the chiral alanine residue at the C-terminus to the primary amine at the N-terminus, 0.9 nm distant. The chiral environment and defined shape produced by the 310 helix brings the amine site into proximity to two exposed amide NHs. Reaction scope studies implied that the amine acts as a Brønsted base and the solvent-exposed NH groups of the helix, shown to weakly bind β-nitrostyrene, are needed to obtain an enantiomeric excess. Replacement of L-alanine with D-phenylalanine gave (Aib)4(D-Phe)NHtBu, a peptide that now catalysed the benchmark reaction with the opposite enantioselectivity. These studies show how achiral residues can play a key role in enantioselective catalysis by peptides through the promotion of folding.

Highly asymmetric aldol reaction of isatins and ketones catalyzed by chiral bifunctional primary-amine organocatalyst on water

Herein, we have reported an environmentally friendly asymmetric aldol reaction between isatins and ketones catalyzed by double-hydrogen-bonded primary amine organocatalysts on water under mild conditions. Enantioenriched 3-hydroxy-2-oxindoles were obtained in high yields (up to 99%) and excellent stereoselectivities (up to 99 : 1 dr and 99% ee) under optimal conditions. Furthermore, the model reaction involving isatin and cyclohexanone was successfully scaled to 10 mmol with no reduction in yield or stereoselectivity. In addition, the catalyst was recovered via simple filtration and was subsequently reused on water, which highlights its good application potential.

Synthesis of Functionalized Five-Membered Heterocycles from Epoxides: A Hydrogen-Bond Donor Catalytic Approach

The synthesis of highly functionalized five-membered oxa- and aza-heterocycles has been reported utilizing hydrogen-bond donor (HBD) catalysis. In this method, an epoxide was taken as a substrate and reacted with functionalized arylidene/alkylidene malononitrile derivatives in the presence of a newly designed HBD catalyst. In all the cases, the products 2,5-disubstituted tetrahydrofurans (2,5-THFs) were obtained in good to excellent yields (up to 86%) with high diastereoselectivity (dr up to 99:1) as a single regioisomer. The stereochemistry at the 2- and 5-positions of the five-membered ring has been confirmed by single-crystal X-ray analysis, and cis is found to be the major product. The same strategy has been further utilized to obtain substituted oxazolidines whenever the epoxide has been reacted with isocyanate as an electrophile. In order to induce enantioselectivity, a chiral epoxide has been reacted with both the electrophiles in the presence of the same catalyst system to afford the single stereoisomer of the final products. This synthetic methodology involves a low catalyst loading and ambient reaction condition and has been generalized with various substituents present in the starting electrophiles to produce the resultant products in acceptable yields and stereoselectivity.

Asymmetric Synthesis of a Quaternary Carbon Stereogenic Center by Organocatalysis Using a Primary Amino Acid and Its Salt

In this personal account, our recent developments on the asymmetric synthesis of a quaternary carbon stereogenic center by organocatalysis using a primary amino acid and its salt as a catalyst are described in three chapters: (1) conjugate addition to nitroalkenes and vinyl ketones, (2) nucleophilic addition to π-allyl palladium complexes, and (3) nucleophilic substitution reactions with allyl and propargyl halides. By these methods, asymmetric α-allylation of α-branched aldehydes and ketones smoothly proceeded to give γ-nitroaldehydes, ketoaldehydes, α-allylated aldehydes, and α-allylated β-ketoesters possessing a quaternary carbon stereogenic center in good yields with high enantioselectivities.

Synthesis and Functionalization of Tertiary Propargylic Boronic Esters by Alkynyllithium-Mediated 1,2-Metalate Rearrangement of Borylated Cyclopropanes

Implementing the use of alkynyllithium reagents in a stereospecific 1,2-metalate rearrangement-mediated ring opening of polysubstituted cyclopropyl boronic esters provides a variety of tertiary pinacol boranes bearing adjacent tertiary or quaternary carbon stereocenters with high levels of diastereomeric purity. The potential of this strategy was demonstrated through a selection of α- and γ-functionalization of the propargyl boronic esters.

Borylated Cyclopropanes as Spring-Loaded Entities: Access to Vicinal Tertiary and Quaternary Carbon Stereocenters in Acyclic Systems

Herein, we present the formation of acyclic frameworks bearing two consecutive stereocenters of either tertiary or quaternary nature starting from easily accessible cyclopropenes. This holistic approach involves a regio- and diastereoselective hydro- or carboborylation of substituted cyclopropenyl esters. Formation of boronate complexes of the latter via the addition of nucleophiles and subsequent stereospecific 1,2-migration with carbon–carbon bond cleavage delivered the title compounds.

Stereospecific Construction of Quaternary Carbon Stereocenters from Quaternary Carbon Stereocenters

Organoaluminum species promote a smooth nucleophilic substitution at the quaternary carbon stereocenter of stereodefined polysubstituted cyclopropyl methyl phosphate with a complete inversion of configuration, even when more reactive functional groups are present. The regio- and diastereoselectivity of the substitution is attributed to the existence of a bicyclobutonium intermediate.

A New Organocatalytic Desymmetrization Reaction Enables the Enantioselective Total Synthesis of Madangamine E

The enantioselective total synthesis of madangamine E has been completed in 30 steps, enabled by a new catalytic and highly enantioselective desymmetrizing intramolecular Michael addition reaction of a prochiral ketone to a tethered β,β′-disubstituted nitroolefin. This key carbon–carbon bond forming reaction efficiently constructed a chiral bicyclic core in near-perfect enantio- and diastereo-selectivity, concurrently established three stereogenic centers, including a quaternary carbon, and proved highly scalable. Furthermore, the pathway and origins of enantioselectivity in this catalytic cyclization were probed using density functional theory (DFT) calculations, which revealed the crucial substrate/catalyst interactions in the enantio-determining step. Following construction of the bicyclic core, the total synthesis of madangamine E could be completed, with key steps including a mild one-pot oxidative lactamization of an amino alcohol, a two-step Z-selective olefination of a sterically hindered ketone, and ring-closing metatheses to install the two macrocyclic rings.

α-Hydroxylation of α,α-Disubstituted N-tert-Butanesulfinyl Ketimines with Molecular Oxygen: Stereoselective Synthesis of α-Tertiary Hydroxyimines

α-Tertiary hydroxyimines were stereoselectively synthesized from enantioenriched N-tert-butanesulfinyl ketimines using potassium tert-butoxide, molecular oxygen, and trimethyl phosphite. The stereoselective hydroxylation of acyclic ketimines bearing two sterically similar α-substituents was achieved by controlling the geometry of the metalloenamine intermediates and the facial selectivity of hydroxylation. The synthetic utility of the resulting α-tertiary hydroxyimines was demonstrated through the successful diastereoselective synthesis of highly substituted β-amino alcohols.

Synergistic Peptide and Gold Catalysis: Enantioselective Addition of Branched Aldehydes to Allenamides

The combination of a peptide catalyst and a gold catalyst is presented for enantioselective addition reactions between branched aldehydes and allenamides. The two catalysts act in concert to provide γ,δ‐enamide aldehydes bearing a fully substituted, benzylic stereogenic center – a structural motif common in many natural products and therapeutically active compounds – with good yields and enantioselectivities. The reaction tolerates a variety of alkyl and alkoxy substituted aldehydes and the products can be elaborated into several chiral building blocks bearing either 1,4‐ or 1,5‐ functional group relationships. Mechanistic studies showed that the conformational features of the peptide are important for both the catalytic efficiency and stereochemistry, while a balance of acid/base additives is key for ensuring formation of the desired product over undesired side reactions.

Asymmetric construction of acyclic quaternary stereocenters via direct enantioselective additions of α-alkynyl ketones to allenamides

Acyclic quaternary stereocenters are widely present in a series of biologically active natural products and pharmaceuticals. However, development of highly efficient asymmetric catalytic methods for the construction of these privileged motifs represents a longstanding challenge in organic synthesis. Herein, an efficient chiral phosphoric acid catalyzed direct asymmetric addition of α-alkynyl acyclic ketones with allenamides has been developed, furnishing the acyclic all-carbon quaternary stereocenters with excellent regioselectivities and high enantioselectivities. Extensive and detailed experimental mechanistic studies were performed to investigate the mechanism of this reaction. Despite a novel covalent allyl phosphate intermediate was found in these reactions, further studies indicated that a SN2-type mechanism with the ketone nucleophiles is not very possible. Instead, a more plausible mechanism involving the elimination of the allyl phosphate to give the α,β-unsaturated iminium intermediate, which underwent the asymmetric conjugate addition with the enol form of ketone nucleophiles under chiral anion catalysis, was proposed. In virtue of the fruitful functional groups bearing in the chiral products, the diverse derivatizations of the chiral products provided access to a wide array of chiral scaffolds with quaternary stereocenters.

Stereodivergent Construction of Vicinal Acyclic Quaternary-Tertiary Carbon Stereocenters by Michael-Type Alkylation of α,α-Disubstituted N-tert-Butanesulfinyl Ketimines

Vicinal quaternary-tertiary carbon stereocenters were constructed with excellent stereoselectivity via aza-enolization of enantioenriched acyclic N-tert-butanesulfinyl ketimines bearing two sterically similar α-linear alkyl substituents followed by conjugate addition to nitroalkenes. Further changes of the absolute configuration of the sulfinyl group and/or the α-stereocenter in the ketimine allowed the facile stereodivergent synthesis of all four diastereomers of the Michael-type alkylation adducts. This reaction is a successful example of acyclic stereocontrol based on stereoselective α-deprotonation for the formation of fully substituted aza-enolates from ketone derivatives.

Water clusters as bifunctional catalysts in organic chemistry: the hydrolysis of oxirane and its methyl derivatives

This contribution explores the bifunctional catalytic activity of water clusters ((H₂O)_n with n = 1-5) in organic chemistry similar to that observed in the formation of H₂SO₄ in acid rain (Chem. Commun., 53, 3516, (2017)). We considered for this purpose the Hydrolysis of Epoxides (HE), in particular, that of oxirane and its methyl derivatives. Surrounding water molecules with H-bond cooperative effects decrease the activation energy of the rate-limiting step of HE in condensed phase, especially when they lead to an anti-periplanar attack on the alkoxide leaving group. Furthermore, the water molecules have a bifunctional catalytic role in HE by (i) increasing the nucleophilic and electrophilic character of the attacking oxygen atom and the leaving group of the reaction, respectively, and (ii) placing the reactants in a suitable disposition for the substitution to occur. Overall, this investigation provides relevant insights into the collective action of water molecules on organic reactions in neutral, basic and acid media.

Stereoselective Sc(OTf)3 -Catalyzed Aldol Reactions of Disubstituted Silyl Enol Ethers of Aldehydes with Acetals

Facile and modular access to stereodefined disubstituted aldehyde-derived silyl enol ethers allowed their successful application in a stereoselective aldol reaction affording the products with excellent yields and diastereomeric ratios. The counter-intuitive stereochemical behavior of this Mukaiyama-aldol reaction is accounted for by a non-classical open transition state.

Palladium-Catalyzed Allenamide Carbopalladation/Allylation with Active Methine Compounds

A palladium-catalyzed allenamide carbopalladation/allylation with active methine compounds has been developed. Various indoles and isoquinolinones bearing a quaternary carbon center were achieved with good efficiency, a broad substrate scope and good functional group tolerance. This reaction underwent cascade oxidative addition, carbopalladation, and allylic alkylation, and two new C-C bonds were formed in one pot.

Asymmetric 1,4-Michael Addition in Aqueous Medium Using Hydrophobic Chiral Organocatalysts

Organic transformations exclusively in water as an environmentally friendly and safe medium have drawn significant interest in the recent years. Moreover, transition metal-free synthesis of enantiopure molecules in water will have a great deal of attention as the system will mimic the natural enzymatic reactions. In this work, a new set of proline-derived hydrophobic organocatalysts have been synthesized and utilized for asymmetric Michael reactions in water as the sole reaction medium. Among the various catalysts screened, the catalyst 1 is indeed efficient for stereoselective 1,4-conjugated Michael additions (dr: >97:3, ee up to >99.9%) resulting in high chemical yields (up to 95%) in a very short reaction time (1 h) at room temperature. This methodology provides a robust, green, and convenient protocol and can thus be an important addition to the arsenal of the asymmetric Michael addition reaction. Upon successful implementation, the present strategy also led to the formation of an optically active octahydroindole, the key component found in many natural products.

Amine Catalysis with Substrates Bearing N-Heterocyclic Moieties Enabled by Control over the Enamine Pyramidalization Direction

Stereoselective organocatalytic C-C bond formations that tolerate N-heterocycles are valuable since these moieties are common motifs in numerous chiral bioactive compounds. Such transformations are, however, challenging since N-heterocyclic moieties can interfere with the catalytic reaction. Here, we present a peptide that catalyzes conjugate addition reactions between aldehydes and nitroolefins bearing a broad range of different N-heterocyclic moieties with basic and/or H-bonding sites in excellent yields and stereoselectivities. Tuning of the pyramidalization direction of the enamine intermediate enabled the high stereoselectivity.

Bifunctional Iminophosphorane Superbase Catalysis: Applications in Organic Synthesis

To improve the field of catalysis, there is a substantial and growing need for novel high-performance catalysts providing new reactivity. To date, however, the set of reactions that can be reliably performed to prepare chiral compounds in largely one enantiomeric form using chiral catalysts still represents a small fraction of the toolkit of known transformations. In this context, chiral Brønsted bases have played an expanding role in catalyzing enantioselective reactions between various carbon- and heteroatom-centered acids and a host of electrophilic reagents. This Account describes our recent efforts developing and applying a new family of chiral Brønsted bases incorporating an H-bond donor moiety and a strongly basic iminophosphorane, which we have named BIMPs (Bifunctional IMinoPhosphoranes), as efficient catalysts for reactions currently out of reach of more widespread tertiary amine centered bifunctional catalysts. The iminophosphorane Brønsted base is easily generated by the Staudinger reaction of a chiral organoazide and commercially available phosphine, which allows easy modification of the catalyst structure and fine-tuning of the iminophosphorane pK_BH+. We have demonstrated that BIMP catalysts can efficiently promote the enantioselective addition of nitromethane to low reactivity N-diphenylphosphinoyl (DPP)-protected imines of ketones (ketimines) to access valuable chiral diamine and α-quaternary amino acid building blocks, and later extended this methodology to phosphite nucleophiles. Subsequently, the reaction scope was expanded to include the Michael addition of high pK_a alkyl thiols to α-substituted acrylate esters, β-substituted α,β-unsaturated esters, and alkenyl benzimidazoles as well as the challenging direct aldol addition of aryl ketones to α-fluorinated ketones. Finally, BIMP catalysts were shown to be used in key steps in the synthesis of complex alkaloid natural products (-)-nakadomarin A and (-)-himalensine A, as well as in polymer synthesis. In most cases, the predictable nature of the BIMP promoted reactions was demonstrated by multigram scale-up while employing low catalyst loadings (down to 0.05 mol%). Furthermore, it was shown that BIMP catalysts can be easily immobilized onto a solid support in one-step for increased catalyst recycling and flow chemistry applications. Alongside our own work, this Account also includes elegant work by Johnson and co-workers utilizing the BIMP catalyst system, when alternative catalysts proved suboptimal.

Deactivation of Secondary Amine Catalysts via Aldol Reaction-Amine Catalysis under Solvent-Free Conditions

Despite intense interest in amine-catalyzed stereoselective reactions, high catalyst loadings of ≥10 mol % are still common and either due to low reactivity or catalyst deactivation. Yet, few deactivation pathways are well understood. Here, we unraveled the deactivation of secondary amines by undesired aldol reaction. Mechanistic studies with peptide and prolinol silyl ether catalysts showed the generality of this so-far underappreciated catalyst deactivation pathway. The insights enabled conjugate addition reactions between aldehydes and nitroolefins on a multigram scale in the absence of solvent-conditions that are attractive as environmentally benign processes-with excellent product yields and stereoselectivities in the presence of as little as 0.1 mol % of a chemoselective peptidic catalyst.

Catalytic Asymmetric Access to Noncanonical Chiral α-Amino Acids from Cyclic Iminoglyoxylates and Enamides

Here we describe an enantioselective Mannich reaction of cyclic iminoglyoxylates with enamides by virtue of chiral phosphoric acid catalysis in a one-pot manner. The wide substrate scope, mild reaction conditions, and constantly excellent enantioselectivities (>95% ee in most cases) render this protocol highly practical for the rapid construction of valuable noncanonical chiral α-amino-acid building blocks.

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.

Straightforward access to densely substituted chiral succinimides through enantioselective organocatalyzed Michael addition of α-alkyl-cyclic ketones to maleimides

A simple, cheap and unchanged organocatalytic system provides efficient access to densely substituted chiral succinimides bearing QCC–TCC vicinal stereocenters from unreactive α-alkyl cyclic ketones and maleimides.

The effect of chiral N-substituents with methyl or trifluoromethyl groups on the catalytic performance of mono- and bifunctional thioureas

We evaluated thiourea organocatalysts that incorporate a chiral group which includes a trifluoromethyl moiety and contrasted their performance with non-fluorinated analogs. The comparison between such systems allows the direct study of the NH acidity of a thiourea bonded to an aliphatic substituent. In principle, -CF3 systems feature an enhanced hydrogen bond (HB) donor capacity that is undoubtedly beneficial for HB-catalysis applied to the Baylis-Hillman reaction. We found that the thiourea substituted on both nitrogens with this group accelerates this reaction like Schreiner's thiourea. On the other hand, we observed a different behavior in reactions promoted by bifunctional catalysts (thiourea-primary amine). In the Michael addition of isobutyraldehyde to methyl benzylidenepyruvate, the -CF3 containing catalysts were better than the -CH3 systems, whereas the conjugate addition to N-phenylmaleimide showed the opposite behavior. Theoretical calculations of the transition states indicated that the phenylethyl group in fluorinated and non-fluorinated compounds have different kinds of interactions with the electrophile. These interactions are responsible for a different arrangement of the electrophile and thereby the selectivity of the catalyst. Therefore, it cannot be generalized that in all cases NH acidity correlates with the performance of the catalyst, particularly, with aliphatic substituents that unlike the aromatic ones possess groups that are outside the plane of the thiourea.

Highly efficient Ir-catalyzed asymmetric hydrogenation of benzoxazinones and derivatives with a Brønsted acid cocatalyst

The Ir-catalyzed highly efficient asymmetric hydrogenation of benzoxazinones and derivatives was successfully developed with N-methylated ZhaoPhos L5 as the ligand, affording various chiral dihydrobenzoxazinones and derivatives with excellent results.

The Ir-catalyzed highly efficient asymmetric hydrogenation of benzoxazinones and derivatives was successfully developed with N-methylated ZhaoPhos L5 as the ligand, which may display a new activation mode with a single anion-binding interaction among the substrate, cocatalyst Brønsted acid and ligand. This synthetic approach afforded a series of chiral dihydrobenzoxazinones and derivatives with excellent results (>99% conversion, 88–96% yields, 91–>99% ee, up to 40 500 TON). A key to success is the utilization of a strong Brønsted acid as the cocatalyst, such as hydrochloric acid, to form a possible single anion-binding interaction with the substrate and catalyst, which greatly contributed to the improvement of reactivity and enantioselectivity. Importantly, a creative and efficient synthetic route was developed to construct the important intermediate for the potential IgE/IgG receptor modulator through our catalytic methodology system.

Organocatalysts Derived from Unnatural α-Amino Acids: Scope and Applications

The organocatalytic properties of unnatural α-amino acids are reviewed. Post-translational derivatives of natural α-amino acids include 4-hydroxy-l-proline and 4-amino-l-proline scaffolds, and also proline homologues. The activity of synthetic unnatural α-amino acid-based organocatalysts, such as β-alkyl alanines, alanine-based phosphines, and tert-leucine derivatives, are reviewed herein. The organocatalytic properties of unnatural monocyclic, bicyclic, and tricyclic proline derivatives are also reviewed. Several families of these organocatalysts permit the efficient and stereoselective synthesis of complex natural products. Most of the reviewed organocatalysts accelerate the reported reactions through covalent interactions that raise the HOMO (enamine intermediates) or lower the LUMO (iminium intermediates).

Enantioselective Michael reaction of anthrone catalyzed by chiral tetraoxacalix[2]arene[2]triazine derivatives

A highly enantioselective Michael addition reaction of anthrone with nitroalkenes by chiral tetraoxacalix[2]arene[2]triazine catalysts was investigated as a novel topic. The stereoselective conversion progressed smoothly by employing 10 mol% of the catalyst and afforded the corresponding Michael adducts with acceptable to high enantioselectivities (up to 97% ee) and very high yields (up to 96%).

A highly enantioselective Michael addition reaction of anthrone with nitroalkenes by chiral tetraoxacalix[2]arene[2]triazine catalysts was investigated as a novel topic.

α-Tetrasubstituted Aldehydes through Electronic and Strain-Controlled Branch-Selective Stereoselective Hydroformylation

Hydroformylation utilizes dihydrogen, carbon monoxide, and a catalyst to transform alkenes into aldehydes. This work applies chiral bisdiazaphospholane (BDP)- and bisphospholanoethane-ligated rhodium complexes to the hydroformylation of a variety of alkenes to produce chiral tetrasubstituted aldehydes. 1,1'-Disubstituted acrylates bearing electron-withdrawing substituents undergo hydroformylation under mild conditions (1 mol % of catalyst/BDP ligand, 150 psig gas, 60 °C) with high conversions and yields of tetrasubstituted aldehydes (e.g., 13:1 regioselectivity, 85% ee, and <1% hydrogenation for 1-fluoromethyl acrylate). The scope also encompasses both acyclic 1,1'-disubstituted and trisubstituted, electron-poor alkenes as well as di- and trisubstituted alkenes composed of small rings with exocyclic and endocyclic unsaturation. For example, 1-methylene-β-lactam furnished the tetrasubstituted aldehyde with 98% selectivity and up to 83% ee. Notably, chiral trisubstituted bicyclic methyleneaziridines are transformed with >99% regioselectivity and >19:1 diastereoselectivity to tetrasubstituted aldehydes at rates >50 catalyst turnovers/hour. NMR studies of the noncatalytic reaction of HRh(BDP)(CO)₂ with methyl 1-fluoroacrylate enable interception of tertiary alkylrhodium intermediates, demonstrating migratory insertion to acyl species is slower than formation of secondary and primary alkylrhodium intermediates. Overall, these investigations reveal how the interplay of sterics, electronics, and ring strain are harnessed to provide access to valuable α-tetrasubstituted aldehyde synthetic building blocks by promoting branched-selective hydroformylation.

Asymmetric Conjugate Addition of α,α-Disubstituted Aldehydes to Nitroalkenes Organocatalyzed by Chiral Monosalicylamides from trans-Cyclohexane-1,2-Diamines

Primary amine-salicylamides derived from chiral trans-cyclohexane-1,2-diamines are used as organocatalysts for the enantioselective conjugate addition of α,α-disubstituted aldehydes to arylated and heteroarylated nitroalkenes. The reaction is performed in the presence of 4-dimethylaminopyridine as an additive in dichloromethane as a solvent at room temperature. The corresponding enantioenriched γ-nitroaldehydes are obtained with enantioselectivities up to 95%. Theoretical calculations are used to justify the reasons of the stereoinduction.