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Transition metal catalysis is one of the most important tools to construct carbon-carbon and carbon-heteroatom bonds in modern organic synthesis. Visible-light photoredox catalysis has recently drawn considerable attention of the scientific community owing to its unique activation modes and significance for the green synthesis. The merger of photoredox catalysis with transition metal catalysts, termed metallaphotoredox catalysis, has become a popular strategy for expanding the synthetic utility of visiblelight photocatalysis. This strategy has led to the discovery of novel asymmetric transformations, which are unfeasible or not easily accessible by a single catalytic system. This contemporary area of organic chemistry holds promise for the development of economical and environmentally friendly methods for the asymmetric synthesis of chiral compounds. In this review, the advances in the enantioselective metallaphotoredox catalysis (EMPC) are summarized.

The amidated peptides are an important class of biologically active compounds due to their unique biological properties and wide applications as potential peptide drugs and biomarkers. Despite the abundance of free amide motifs (Asn, Gln, and C-terminal amide) in native peptides, late-stage modification of the amide unit in naturally occurring peptides remains very rare because of the intrinsically weak nucleophilicity of amides and the interference of multiple competing nucleophilic residues, which generally lead to undesired side reactions. Herein, chemoselective arylation of amides in unprotected polypeptides has been developed under an air atmosphere to afford the N-aryl amide peptides bearing various functional motifs. Its success relies on the combination of gold catalysis and silver salt to differentiate the relative inert amide among a collection of reactive nucleophilic amino acid residues (e.g., −NH2, −OH, and −COOH), favoring the C–N bond coupling toward amides over other more nucleophilic groups. Experimental and DFT studies reveal a crucial role of the silver cation, which serves as a transient coordination mask of the more reactive reaction sites, overcoming the inherently low reactivity of amides. The excellent biocompatibility of this strategy has been applied to functionalize a wide range of peptide drugs and complex peptides. The application could be further extended to peptide labeling and peptide stapling.

We report the 1,6-addition of acyl radicals to the electron-deficient 1,3-dienes under visible-light photoredox catalysis. The deoxygenative allylation of the carboxylic acid is achieved under mild conditions, generating the valuable 1,6-dicarbonyl compounds in moderate to good yields (up to 96%). A range of functionalized carboxylic acids are competent coupling partners. This deoxygenative allylation protocol has a high level of regio- and stereo-selectivity as well as good functional group comparability.

We report a thioacylation transfer reaction based on nickel-catalyzed C–C bond cleavage of thioesters with sp2-hybridized electrophiles. Aryl bromides, iodides, and alkenyl triflates can participate in thioester transfer reaction of aryl thioesters, affording a wide range of structurally diverse new thioesters in yields of up to 98% under mild reaction conditions. With this protocol, it is possible to construct alkenyl thioesters from the corresponding ketones through the generation of alkenyl triflates.

We report an unprecedented C–H bond functionalization of cyclopropenes enabled by dinuclear gold catalysis. Highly selective C–H allylation, alkynylation and halogenation of cyclopropenes with organic halides have been realized. The reaction does not require strong external oxidants and affords access to functionalized cyclopropenes in moderate to good yields. The reductive elimination process to controllably construct C–C or C–X bonds can be tuned by using different dinuclear gold catalysts.

Deconstructive functionalization of cyclic amines can provide access to chemicals with diverse skeletons. We report the conversion of tertiary amines to thiocarbamoyl fluorides, a reaction enabled by photoredox catalysis and tolerating different functional groups while avoiding strong oxidants. A one-pot synthetic method from tertiary amines and AgF has been developed to get access to trifluoromethylamines. The synthesized thiocarbamoyl fluorides can be further transferred into esters.

The chemistry of hydrazones has gained great momentum due to their involvement throughout the evolution of organic synthesis. Herein, we discuss the tremendous developments in both the methodology and application of hydrazones. Hydrazones can be recognized not only as synthetic equivalents to aldehydes and ketones but also as versatile synthetic building blocks. Consequently, they can participate in a range of practical synthetic transformations. Furthermore, hydrazone derivatives display a broad array of biological activities and have been widely applied as pharmaceuticals. Owing to the weak directing group effect of simple aldehydes and ketones in C–H bond functionalizations, the C–H bond functionalizations of hydrazones that have been developed in the past five years represent a significant step forward. These novel transformations open a new door to a broader library of functionalized and complex small molecules. Moreover, a wide range of biologically important N-heterocycles (dihydropyrazoles, pyrazoles, indazoles, cinnolines, etc.) can be efficiently synthesized in an atom- and step-economical manner through single, double, or triple C–H bond functionalizations of hydrazones. Both radical C–H functionalizations and transition-metal-catalyzed directing-group strategies have enhanced the synthetic utility of hydrazones in the chemical community because these strategies solve the long-standing challenge of C–H functionalizations adjacent to aldehydes and ketones.

Domino-fluorination–protodefluorination decarboxylative cross-coupling of α-keto acids with styrene has been developed via photoredox catalysis. The critical part of this strategy is the formation of the carbon–fluorine (C–F) bond by the capture of a carbon-centered radical intermediate, which will overcome side reactions during the styrene radical functionalization process. Experimental studies have provided evidence indicating a domino-fluorination–protodefluorination pathway with α-keto acid initiating the photoredox cycle. The present catalytic protocol also affords a novel approach for the construction of α,β-unsaturated ketones under mild conditions.

Transition-metal-catalysed, redox-neutral dehydrosilylation of alkenes is a long-standing challenge in organic synthesis, with current methods suffering from low selectivity and narrow scope. In this study, we report a general and simple method for the manganese-catalysed dehydrosilylation and hydrosilylation of alkenes, with Mn2(CO)10as a catalyst precursor, by using a ligand-tuned metalloradical reactivity strategy. This enables versatility and controllable selectivity with a 1:1 ratio of alkenes and silanes, and the synthetic robustness and practicality of this method are demonstrated using complex alkenes and light olefins. The selectivity of the reaction has been studied using density functional theory calculations, showing the use of an iPrPNP ligand to favour dehydrosilylation, while a JackiePhos ligand favours hydrosilylation. The reaction is redox-neutral and atom-economical, exhibits a broad substrate scope and excellent functional group tolerance, and is suitable for various synthetic applications on a gram scale.

An operationally simple and highly selective Au/Ag bimetallic-catalyzed cross-dehydrogenative biaryl coupling between pyrazoles and fluoroarenes has been developed. With this reaction, a wide range of biheteroaryl products can be obtained in moderate to good yields with excellent functional group compatibility. The exact role of silver salts, previously overlooked in most gold-catalyzed transformations, has been carefully investigated in this biaryl coupling. Insightful experimental and theoretical studies indicate that silver acetate is the actual catalyst for C–H activation of electron-poor arenes, rather than the previously reported gold(I)-catalyzed process. An unprecedented Au/Ag dual catalysis is proposed, in which silver(I) is responsible for the activation of electron-poor fluoroarenes via a concerted metalation–deprotonation pathway, and gold(III) is responsible for the activation of electron-rich pyrazoles via an electrophilic aromatic substitution process. Kinetic studies reveal that ArFnAu(III)-mediated C–H activation of pyrazoles is most likely the rate-limiting step.

The annulation reactions of N-allylbenzamides with N-sulfonylaminopyridinium salts were developed under metal-free photoinduced mild conditions. Substituent-controlled sulfonaminoarylation and sulfonaminooxylation of benzamides were realized: N-allylbenzamides lead to benzosultams, while N-(2-phenylallyl)benzamides give sulfonamidylated oxazoline derivatives. Control experiments indicated that those reactions undergo a radical pathway with arylsulfonamidyl radicals as the intermediates. The aryl C–H bond functionalization in arylsulfonamidyl was involved for the first time to give benzosultams.

The classical Au(I)/Au(III) redox couple chemistry has been limited to constructing C–C and C–X bonds, and thus, the exploration of the elementary reaction of gold redox coupling is very significant to enrich its organometallic features. Herein, we report the first visible-light-mediated, external oxidant-free Au(I)/Au(III) redox couple using commercially available Mn2(CO)10to generate Mn–Au(III)–Mn intermediates for bimetallic redox coupling. A wide range of structurally diverse heterodinuclear and polynuclear L–Au(I)–Mn–L′ complexes (19 examples, up to >99% yields) are readily constructed, providing a robust strategy for the concise construction of Au–Mn complexes under mild reaction conditions. The mechanistic studies together with DFT calculations support the radical oxidative addition of •Mn(CO)5to gold and bimetallic reductive elimination mechanisms from highly active Mn–Au(III)–Mn species, representing an important step toward an elementary reaction in gold chemistry research. Furthermore, the resulting Au–Mn complexes exhibit unique catalytic activity, with which divergent reductive coupling of nitroarenes can readily afford azoxybenzenes, azobenzenes, and hydrazobenzenes in moderate to good yields.

Modular diboronic acid receptors R‐1and S‐1were synthesized and found to be selective fluorescent chemosensors for saccharides. The fluorescence intensity of R‐1and S‐1increased on addition of saccharides due to the formation of intramolecular 1:1 cyclic complexes. In general, R‐1has higher binding constants and produces a higher fluorescent response with saccharides than S‐1.

A breath of fresh air: The title reaction has been developed for the coupling of amines with nitroalkanes and different unmodified ketones using air as the sole oxidant under mild reaction conditions. The safe, convenient, and environmentally benign process, as well as the low catalyst loading, short reaction time, and good yields make this protocol very practical (see scheme).

„Tief Luftholen“ist angesagt für die Titelreaktion, die Amine unter milden Bedingungen mit Nitroalkanen und nichtmodifizierten Ketonen kuppelt, denn dabei dient Luft alleine als Oxidationsmittel. Der praktische Prozess kommt mit geringen Katalysatormengen aus und liefert die Produkte nach kurzen Reaktionszeiten in guten Ausbeuten.

A highly efficient organocatalytic enantioselective CS bond formation reaction between simple alkyl thiols and Morita–Baylis–Hillman (MBH) carbonates is described. The optically active α‐methylene β‐mercapto esters could be obtained under mild reaction conditions with excellent enantioselectivities (up to 97% ee). The broad scope and simple operation make this methodology very practical.

Amination under the mask: The asymmetric allylic amination of MBH carbonates was achieved with masked ammonia (benzophenone imine) under the catalysis of modified cinchona alkaloids to give good yields with excellent enantioselectivities (up to 99 % ee) for a wide range of MBH carbonates (see scheme).

Two boron‐contained fluorescent sensors, 1and 2, based on coumarin have been prepared. The fluorescence response of the two systems was investigated with addition of saccharide and mercury ions. Sensor 2behaves as a bifunctional fluorescent switch with chemical inputs of D‐fructose and mercury ions.

Mercury rising: A Highly Selective and sensitive polymer‐based fluorescence sensor synthesized using click reactions affords the most‐pronounced fluorescence response to Hg2+ions.

In prime condition: The hydrolysis of a chiral diimine precursor can be carried out by a Brønsted acid to form an in situ primary amine–imine intermediate as a bifunctional primary aminocatalyst, which promoted direct asymmetric aldol reactions between α‐keto esters and ketones in high yields (up to 88 %) and with excellent enantioselectivities (see scheme; R1, R2, R4=alkyl; R3=aryl).

The highly effective and enantioselective sulfenylation of β‐keto phosphonates catalyzed by α,α‐diaryl‐L‐prolinols has been developed. The optically active α‐sulfenylated β‐keto phosphonates could be obtained under mild reaction conditions in good yields (up to 92%) and with excellent enantioselectivities (up to 92% ee).

A chiral polymer incorporating an (R,R)‐salen moiety was synthesized by the polymerization of (R,R)‐1,2‐diaminocyclohexane with 2,5‐dibutoxy‐1,4‐di(salicyclaldehyde)‐1,4‐diethynyl‐benzene by a nucleophilic addition–elimination reaction. The fluorescence responses of the (R,R)‐salen‐based polymer toward various metal ions were investigated by fluorescence spectra. Compared with other cations, such as Na+, K+, Mg2+, Ca2+, Mn2+, Fe2+, Fe3+, Co2+, Ni2+, Cu2+, Ag+, Cd2+, Hg2+, and Pb2+, Zn2+can lead to a pronounced fluorescence enhancement as high as 7.8‐fold together with an obvious blue‐shift change of the chiral polymer. More importantly, the fluorescent color of the polymer changed to bright blue instead of weak yellow after addition of Zn2+, which can be easily detected by the naked eye. The results indicate that this kind of chiral polymer, incorporating an (R,R)‐salen moiety as a receptor in the main chain backbone, can exhibit high sensitivity and selectivity for Zn2+recognition.

A novel imidazolium iontagged Lproline catalyst has been developed. The asymmetric αaminoxylation of aldehydes and ketones with excellent enantioselectivities, up to 99% ee, and high yields in ionic liquids has been achieved. The system can be easily recycled and reused for at least six times without significant loss of yields and enantioselectivity.

A new mode of activation: The asymmetric diarylprolinol‐catalyzed α‐sulfenylation of β‐ketoesters provides the products in good‐to‐excellent enantioselectivities and yields. Studies suggest that the sterically bulky secondary amines activate β‐ketoesters through hydrogen bonding. Lg=leaving group.

A chiral heterobimetallic Lewis acid complex has been developed as an efficient catalyst. The enantioselective desymmetrization of mesoepoxides with aryl selenols and thiols catalyzed by the heterobimetallic complex has been optimized. The optically active βarylseleno alcohols and βhydroxy sulfides were obtained in good yields and high enantioselectivities up to 97% eeand 92% ee, respectively. A strong synergistic effect between different Lewis acids was exhibited in the catalytic process.

Direct nucleophilic substitution of allylic alcohols with various nitrogen, oxygen, and carbon nucleophiles catalyzed by MoO2acac2was realized. The corresponding products were obtained in moderatetoexcellent yields. Studies of the reaction mechanism showed that a carbenium intermediate was formed in the transition state. © WileyVCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009

Chiral organoselenium compounds can be attained from three types of asymmetric synthesis. Chiral substratecontrolled methods, chiral auxiliary-controlled methods, and chiral catalyst-controlled methods toward optically active organoselenium derivatives were illustrated. The strategy and classification of methods underlying all asymmetric synthesis therefore involve enantiomerically pure compounds to influence the stereochemical outcome of the reactions. In this review, the advances in asymmetric synthesis of some important classes of chiral organoselenium compounds were described.

A new calixarene-like salen ligand is efficiently prepared from 2,6-bishydroxymethyl-4- TERT-butyl phenol as starting material by a five-step synthesis. The enantioselective Friedel-Crafts reactions of aromatic amine with glyoxylate are examined employing a titanium derivative of this new ligand as the chiral catalyst, and provide modest to excellent enantioselectivities up to 98% ee.

The efficient asymmetric preparation of the C2-symmetric chiral 1,4-diamine, (1R,2S,4R,5S)-1,4-diamino-2,5-dimethylcyclohexane (5), and its salen ligands is described. With the Mitsunobu reaction as the key step, the overall yield of the four-step synthesis of 5 is 45%. The enantioselective alkynylation of meso- epoxides catalyzed by chiral gallium complexes is also achieved.

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Various electron-rich aromatic and olefinic donors (D) are readily converted to their cation radicals (D⁺&z.rad;) in the presence of strong protic acids, even in nonpolar solvents such as dichloromethane. By using the three prototypical organic donors octamethylbiphenylene (OMB), adamantylideneadamantane (AA) and the isomeric fused homoadamantene (FHA), we identify the protonated donor (D-H⁺) as the effective oxidant for electron transfer from the organic donor (i.e., D-H⁺ + D → D-H&z.rad; + D⁺&z.rad;). The subsequent reduction of (D-H&z.rad;) to the dihydro product D-H₂ is demonstrated by the isolation of 2,2'-biadamantane, the structure of which is established by X-ray crystallography.

Enantioselective conjugate addition of benzotriazole to α,β-enones catalyzed by prolinol derivatives with moderate yields and enantioselectivities was reported. Studies of stereoelectronic effects of the catalyst showed that the transition state could be of a hydrogen bonding activation mode, and fine tuning of the substituents on the aryl moiety of the catalyst is important for the reaction stereoselectivities.

The first example of salan-vanadium catalyzed enantioselective ring-opening of meso-epoxides has been reported, which furnished β-hydroxy sulfides in good yields and moderate enantioselectivities.

The desymmetrization ring opening of meso epoxides using trimethylsilyl cyanide catalyzed by organogallium and indium complexes with binaphthol monoether derivatives as chiral ligands gave β-isocyanohydrins with moderate to excellent enantioselectivities of up to 95% ee.

The products are purified by crystallization.

A highly efficient asymmetric reaction of Morita—Baylis—Hillman carbonates (I) and (IV) with alkyl mercaptans (II) is achieved in the presence of MgSO4and (DHQD)2‐PHAL as organocatalyst.