A copper catalyst system derived from TaoPhos and CuF₂ was used successfully for catalytic asymmetric Huisgen [3+2] cycloaddition of azides and alkynes to give optically pure products containing succinimide- and triazole-substituted quaternary carbon stereogenic centers. The desired products were obtained in good yields (60–80 %) and 85:15 to >99:1 enantiomeric ratio (e.r.) in this click cycloaddition reaction.

The construction of carbon–silicon bonds is highlighted as an exciting achievement in the field of organosilicon chemistry and green chemistry. Recent developments in this area will enable the sustainable chemical conversion of silicon resources into synthetically useful compounds. Especially, the catalytic silylation through CH bond activation without directing groups and hydrogen acceptors is one of the most challenging topics in organic chemistry and green chemistry. These remarkable findings on catalytic silylation can pave the way to a more environmentally benign utilization of earth-abundant silicon-based resources in synthetic chemistry.

In den letzten Jahren gab es bemerkenswerte Fortschritte bei der enantioselektiven Silylierung von Alkoholen. Durch die erfolgreiche Anwendung in der regio- und stereoselektiven Funktionalisierung von Hydroxygruppen verwandelte sich die Silyletherbildung von einer einfachen Reaktion zum Schutz funktioneller Gruppen in ein leistungsfähiges enantioselektives Verfahren. Dieser Kurzaufsatz fasst die jüngsten Ergebnisse in diesem aufstrebenden Gebiet zusammen.

A palladium-catalyzed allylic alkylation of unsubstituted 2-cyanoacetates using a 1,1′-bi-2-naphthol-derived multifunctional N,O,P ligand is reported. A number of chiral monosubstituted 2-cyanoacetates with two adjacent stereogenic carbon centers are obtained in this Pd-catalyzed asymmetric allylic alkylation reaction, in which the multistereogenic and multifunctional 1,1′-bi-2-naphthol-derived N,O,P ligand-promoted Pd-catalyzed asymmetric allylic alkylation reaction proceeds smoothly in high diastereo- and enantioselectivity (up to >99:1 dr and up to 96 % ee).

In recent years, remarkable progress has been made in the enantioselective silylation of alcohols. Owing to the successful site- and stereoselective functionalization of hydroxy groups, silyl ether formations have evolved from being a simple reaction for functional-group protection into a powerful enantioselective process. In this Minireview, we highlight important recent findings in this emerging field.

In this work, we have developed a new approach to monodispersed hybrid Ag@TiO₂ nanocomposites using a titanium-promoted cross-linking reduction in the SiH functional material, polymethylhydrosiloxane (PMHS)-based semi-interpenetrating networks (PMHSIPN). The titania was designed to be highly dispersed on the functional material and then the Ag@TiO₂ nanoparticles were formed in uniform size and shape under mild conditions. The experimental results reveal that the nanosilver catalysts (the fabricated Ag@TiO₂ located on the PMHSIPNs, namely, nanoAg@TiO₂@PMHSIPN) have enhanced catalytic activities in the alkynylation of trifluoromethyl ketones or α,β-unsaturated trifluoromethyl ketones with terminal alkynes. In this reaction, the hybrid Ag@TiO₂ nanoparticles exhibited a high level of catalytic activity for the selective 1,2-alkynylation of various trifluoromethyl ketones and α,β-unsaturated trifluoromethyl ketones into a wide range of fluorinated alcohols in water. Finally, on the basis of the nanoAg@TiO₂@PMHSIPN-catalyzed alkynylation of trifluoromethyl ketones, we developed a new concept whereby highly reactive substrates act as a “reactive tractor” or “reactive springboard” to drive the transformation of poorly reactive substrates as springboard chemistry. Consequently, we found that trifluoromethyl ketone can be used as an efficient additive in the nanosilver-catalyzed alkynylation of aldehydes.

We have demonstrated a highly diastereoselective synthesis of optically pure Ar-BINMOL-derived diols and their analogues. The present study demonstrates a unique cascade chirality transfer in a [1,2]-Wittig rearrangement that leads to chiral diols with three stereogenic centers, which include a chiral sp³ center at the alcohol and C₂-axial chirality. Screening these ligands in the arylation of aromatic aldehydes with Grignard reagents shows that the naphthyl-substituted BINMOL promotes the aryl transfer reaction in good yields (70–92 %) and moderate-to-good enantioselectivities (up to 72 % ee), and a series of control experiments substantiates that the axial chirality and the chiral sp³ center at the alcohol of the Ar-BINMOLs are the pivotal enantioselectivity-controlling structure elements. In addition, this study demonstrated the importance of the chiral sp³ center at the alcohol on Ar-BINMOL for the aryl transfer reaction. Finally, we found that the chiral Ar-BINMOL ligand 2h mediated the titanium-promoted 1,2-addition of MeMgBr to aldehydes to give the desired products in good yields with excellent enantioselectivities (up to 92 % ee).

In this work, we have successfully synthesized a new family of chiral Schiff base–phosphine ligands derived from chiral binaphthol (BINOL) and chiral primary amine. The controllable synthesis of a novel hexadentate and tetradentate N,O,P ligand that contains both axial and sp³-central chirality from axial BINOL and sp³-central primary amine led to the establishment of an efficient multifunctional N,O,P ligand for copper-catalyzed conjugate addition of an organozinc reagent. In the asymmetric conjugate reaction of organozinc reagents to enones, the polymer-like bimetallic multinuclear CuZn complex constructed in situ was found to be substrate-selective and a highly excellent catalyst for diethylzinc reagents in terms of enantioselectivity (up to >99 % ee). More importantly, the chirality matching between different chiral sources, C₂-axial binaphthol and sp³-central chiral phosphine, was crucial to the enantioselective induction in this reaction. The experimental results indicated that our chiral ligand (R,S,S)-L1- and (R,S)-L4-based bimetallic complex catalyst system exhibited the highest catalytic performance to date in terms of enantioselectivity and conversion even in the presence of 0.005 mol % of catalyst (S/C=20 000, turnover number (TON)=17 600). We also studied the tandem silylation or acylation of enantiomerically enriched zinc enolates that formed in situ from copper-L4-complex-catalyzed conjugate addition, which resulted in the high-yield synthesis of chiral silyl enol ethers and enoacetates, respectively. Furthermore, the specialized structure of the present multifunctional N,O,P ligand L1 or L4, and the corresponding mechanistic study of the copper catalyst system were investigated by ³¹P NMR spectroscopy, circular dichroism (CD), and UV/Vis absorption.

This minireview focuses on the recent advances in the synthetic application of amino acid-derived bifunctional phosphine catalysts bearing a hydrogen-bond donor. In the examples illustrated, the amino acid-based phosphines have already been proven to be versatile, catalyzing a wide range of asymmetric reactions, including (aza)-MBH reactions, [3+2] cyclizations, [4+2] cycloadditions, allylic alkylation, and Michael addition.

A combined catalyst system of a cinchonidine-derived primary amine and triphenylphosphine (CD-NH₂/PPh₃) exhibited high catalytic performance in the Michael reaction of aldehydes with maleimides, thereby affording the corresponding functionalized aldehydes in excellent yields (up to 99 %) and enantioselectivities (>99 % ee). More interestingly, the significance of the phosphine in enhancing the enantioselectivities in the chiral-primary-amine-catalyzed Michael reaction was revealed. Furthermore, we explored the origin of the reaction mechanism in the Michael addition promoted by the dual organocatalytic system. On the basis of experimental results and spectroscopic analysis, such as UV/Vis, fluorescence emission (FL), NMR, and circular dichroism (CD) spectroscopy, as well as ESI-MS, we found that the molecular assembly of phosphine and primary amine played a crucial role in this enantioselective reaction, in which a possible supramolecular complex was formed as an effective chiral catalyst through noncovalent molecular interactions of a cinchona alkaloid-derived primary amine with triphenylphosphine.

A very simple, direct, bismuth-catalyzed conjugate reduction protocol that allows for the catalytic regioselective formation of substituted ketones from enones under mild conditions has been developed. We have shown for the first time that the combined poly(methylhydro)siloxane-malononitrile system can serve as an efficient reductant/reagent in 1,4-conjugate reduction of enones. The regioselectivity, efficiencies, and experimental simplicity of the present method complements the more complex methods previously employed in copper or palladium-catalyzed reduction. This method should prove attractive because of its mild reaction conditions and the interesting chemistry of combining the use of poly(methylhydro)siloxane and malononitrile for selective reduction.

An unprecedented lateral sequential lithiation/silylation/condensation of tertiary aromatic amides has been developed that provides an efficient method to build up functional olefins in good yields. In addition, we have established an efficient and simple method that involves UV/Vis, fluorescence, and NMR analyses, to detect the interaction between transition-metal salts and functional olefins containing tertiary amides. This has enabled a highly efficient palladium-catalyzed Suzuki coupling reaction in the presence of tertiary aromatic amide-derived olefin ligands to be developed. The best results were obtained by employing 2 mol-% Pd(OAc)₂, 2 equiv. Cs₂CO₃, a reaction temperature of 80 °C, dioxane as the solvent, and phosphane-free olefin 2d as ligand.

An interesting example of a divergent catalysis with a copper(I) and amine-functional macromolecular polysiloxanes system was successfully presented in click chemistry. In this manuscript, we demonstrate the remarkable ability of the secondary amine-functional polysiloxane to induce oxidative coupling in the copper-mediated Huisgen reactions of azides and alkynes, thereby achieving good yields and selectivities. The click reactions mediated by a polysiloxane-supported secondary amine allow the preparation of novel heterocyclic compounds, that is, bistriazoles. Comparably, it is also surprising that the use of a diamine-functional polysiloxane as ligand led to a classic Huisgen [3+2] cycloaddition in excellent yields. From the results of the present amine-functional polysiloxanes-controlled Huisgen reaction or oxidative Huisgen coupling reaction to divergent products and the proposed mechanism, we suggested that the mononuclear bistriazole–copper complex stabilized and dispersed by the secondary amine-functional polysiloxane was beneficial to prevalent the way to oxidative coupling.

A highly efficient catalytic protocol for the isomerization of substituted amide-derived olefins is presented that successfully uses a hydride palladium catalyst system generated from [PdCl₂(PPh₃)₂] and HSi(OEt)₃. The Z to E isomerization was carried out smoothly and resulted in geometrically pure substituted olefins. Apart from the cis–trans isomerization of double bonds, the selective reduction of terminal olefins and activated alkenes was performed with excellent functional group tolerance in the presence of an amide-derived olefin ligand, and the products were obtained in high isolated yields (up to >99 %). Furthermore, the palladium/hydrosilane system was able to promote the reductive decarbonylation of benzoyl chloride when a (Z)-olefin with an aromatic amide moiety was used as a ligand.

The one-pot, organocatalytic Hayashi sequential reaction (HSR) of β-nitroacrylate, aldehyde, toluenethiol, and ethyl 2-(diethoxyphosphoryl)acrylate allowed the synthesis of almost stereoisomerically pure, highly functionalized polysubstituted cyclohexanes with very high diastereo- and enantio-selectivity (up to > 99 % ee). The one-pot synthesis consists of the tertiary amine modified diarylprolinol silyl ether-mediated asymmetric Michael reaction, a domino Michael reaction/Horner–Wadsworth–Emmons reaction, and a sulfa-Michael reaction. In addition, we have also demonstrated an improved protocol for the domino oxa-Michael/aldol reaction of salicyladehydes with α,β-unsaturated aldehydes with recyclable tertiary amine-modified diarylprolinol silyl ether 3d as an effective organocatalyst, which results in the formation of chiral chromenes with good enantioselectivities (up to 94 % ee). UV/Vis and CD spectroscopy provide a cross-validation method to elucidate the slight difference between electron-withdrawing 3d and diphenylprolinol silyl ether 3a, which can give indirect evidence for the enhancement of enantioselective induction with 3d in the above transformations.

2′-Hydroxy-1,1′-binaphthalene-2-(arylmethanol) (Ar-BINMOLs), a family of new 1,1′-binaphthalene-2,2′-diol derivatives, prepared by a [1,2]-Wittig rearrangement, are introduced as new chiral molecules for the study of the modes of supramolecular aggregation on the basis of ESI-MS, NMR spectroscopy, differential scanning calorimetry (DSC), and X-ray diffractometry. Characterization showed that Ar-BINMOLs exhibit different characteristics to BINOL and act as supramolecules due to hydrogen bonding and aromatic π–π/C–H···π interactions. In particular, CD measurements of chiral and racemic Ar-BINMOL 2a in solution and the solid state show a strong Cotton effect, which revealed that amplification of chirality was observed because of the formation of a chiral supramolecular oligomer derived from the racemic monomer. To this end, the Ar-BINMOLs were used as supramolecular auxiliaries to mediate the Michael reaction of anthrone to (E)-β-nitrostyrene and could give the Michael adduct with comparable enantioselectivities. In addition, the Ar-BINMOLs act as ligands to promote asymmetric 1,2-addition of diethylzinc to aldehydes, which resulted in excellent yields and enantioselectivities (up to >99.9 % ee) in the reactions of diethylzinc with a broad range of aromatic aldehdyes.

A highly enantioselective Friedel–Crafts alkylation of indoles with α,β-unsaturated aldehydes with excellent enantioselectivities (up to >99 % ee) has been developed, and this improved method offers substantial advantages over traditional approaches, not only by avoiding the use of acids or bases, but also in terms of the higher level of stereoselectivity. In addition, we have demonstrated through a plausible mechanism that the role of silicon in the diarylprolinol silyl ethers (Jørgensen–Hayashi organocatalyst) not only serves as a bulky group to induce steric repulsion but also serves as a Lewis acidic promoter to accelerate the reaction between the secondary amine and the substrate (α,β-unsaturated aldehyde).

A novel metal-free intramolecular Brønsted-acid-catalyzed domino deprotection–hydrosilylation with hydrosilanes has been developed, and the unexpected Brønsted-acid-catalyzed intermolecular hydrolytic oxidation to functional siloxanes was described for the divergent and facile synthesis of functionalized siloxanes containing aldehyde motifs. We propose that these reactions proceed via neighboring acetal-assisted Si–H bond activation. In addition, a related reaction is expected to open up further opportunities for the development and application of functional organosilicon compounds by organocatalysis.

A facile and practical methodology for the synthesis of synthetically useful diarylmethanol-based 1,4-diols and enantiomerically pure BINOL-derived diols with axial and sp³-central chirality has been developed through neighboring lithium-promoted [1,2]-Wittig rearrangement. The chirality transfer process shows a broad substrate scope in terms of the aromatic ether substituent, which allows access to a broad of range of chiral 1,1′-binaphthalene-2-α-arylmethanol-2′-ols with excellent enantioselectivities (>99 % enantiomeric excess) and yields (84–96 %). This should be considered as an available and attractive chiral source to design and prepare privileged ligands or catalysts.

A detailed experimental investigation of an aza-Michael reaction of aniline and chalcone is presented. A series of Cinchona alkaloid-derived organocatalysts with different functional groups were prepared and used in the aza-Michael and retro-aza-Michael reaction. There was an interesting finding that a complete reversal of stereoselectivity when a benzoyl group was introduced to the cinchonine and cinchonidine. The chirality amplification vs. time proceeds in the quinine-derived organocatalyst containing silicon-based bulky group, QN-TBS, -catalyzed aza-Michael reaction under solvent-free conditions. In addition, we have demonstrated for the first time that racemization was occurred in suitable solvents under mild conditions due to retro-aza-Michael reaction of the Michael adduct of aniline with chalcone. These indicate the equilibrium of retro-aza-Michael reaction and aza-Michael reaction produce the happening of chirality amplification in aza-Michael reaction and racemization via retro-aza-Michael reaction under different conditions, which would be beneficial to the development of novel chiral catalysts for the aza-Michael reactions. Chirality, 2011. © 2011 Wiley-Liss, Inc.

Recent years have witnessed an explosive growth in the field of amino organocatalysis, especially in asymmetric enamine and iminium catalysis. Except for the obvious interaction between organocatalyst and substrate, the impact of bulky side group ons stereoselectivity is not as simple as one could imagine. Within the development of bulky site-stereoselective organocatalysts, functional silyl organocatalysts with a bulky silicon group are promising and meet the high standards of modern synthetic methods. This review focuses on the recent advances in the synthetic applications of silicon-based, bulky amino organocatalysts in which catalysts containing an organosilicon moiety or group play a formative role in controlling both the course of the reaction as well as the stereoselectivity.

A very simple method was developed for the direct, palladium-free catalytic α-allylic alkylation of aldehydes. The direct organocatalytic intermolecular α-allylic alkylation reaction was mediated by a simple combination of Brønsted acid and enamine catalysis which furnished α-allylic alkylated aldehydes and cyclohexanone in high yields and chemoselectivities. The reaction conditions are mild and environmental friendly, the process is conducted under an atmosphere of air without the need for dried solvents, and water is the only side product of the allylic alkylation reaction.

A series of chiral organocatalysts and Lewis acids have been evaluated in the Lewis acid/organocatalysts-based cooperative catalytic Biginelli reaction, which resulted in the determination of a novel cooperative Lewis acid/primary amine catalyst system, NbCl₅/QN-NH₂. The synergistic effect of NbCl₅ and the quinine-derived primary amine is pronounced and gave dihydropyrimidiones (DHPMs) in moderate to good enantioselectivities (up to 84 % ee) and good to excellent yields (up to 99 % yield) under mild conditions.