(P

A novel class of (P^N^C) pincer ligands capable of stabilizing elusive gold(III) species is reported here. Straightforward access to (P^N^C)gold(III) hydroxo, formate, and hydride complexes has been streamlined by first incorporating a cycloauration step devoid of toxic metals or harsh conditions. The resulting gold complexes exhibit remarkable stability in solution as well as in the solid state under ambient conditions, which enabled their characterization by X-ray diffraction analyses. Interestingly, the influence of the ligand allowed the preparation of gold(III)-hydrides using mild hydride donors such as H-Bpin, which contrasts with sensitive super hydrides or strong acids and cryogenic conditions employed in previous protocols. A detailed bonding characterization of these species is complemented by reactivity studies.

Dual Nickel/Photoredox-Catalyzed Asymmetric Carbamoylation of Benzylic C(sp3 )-H Bonds.

Radical-mediated Hydrogen Atom Abstraction of Csp3 -H bonds has become a powerful tool for the asymmetric functionalization of organic feedstocks. Here, we present an asymmetric synthesis of α-aryl amides via carbamoylation of alkylarenes with isocyanates as electrophiles. The synergistic combination of a photoredox and a chiral nickel-catalyst, enables the use of readily available and neutral reagents under mild reaction conditions and provides straightforward access to pharmacologically relevant motifs in enantiomerically pure form.

Asymmetric α-Chlorination of ß-Keto Esters Using Hypervalent Iodine-Based Cl-Transfer Reagents in Combination with Cinchona Alkaloid Catalysts.

We herein report an unprecedented strategy for the asymmetric α-chlorination of ß-keto esters with hypervalent iodine-based Cl-transfer reagents using simple Cinchona alkaloid catalysts. Our investigations support an α-chlorination mechanism where the Cinchona species serves as a nucleophilic catalyst by reacting with the chlorinating agent to generate a chiral electrophilic Cl-transfer reagent in situ. Using at least 20 mol-% of the alkaloid catalyst allows for good yields and enantioselectivities for a variety of different ß-keto esters under operationally simple conditions.

Nickel-Catalyzed Asymmetric Synthesis of α-Arylbenzamides.

A nickel-catalyzed asymmetric reductive hydroarylation of vinyl amides to produce enantioenriched α-arylbenzamides is reported. The use of a chiral bisimidazoline (BIm) ligand, in combination with diethoxymethylsilane and aryl halides, enables the regioselective introduction of aryl groups to the internal position of the olefin, forging a new stereogenic center α to the N atom. The use of neutral reagents and mild reaction conditions provides simple access to pharmacologically relevant motifs present in anticancer, SARS-CoV PLpro inhibitors, and KCNQ channel openers.

Synthesis of Cyclic Organic Carbonates Using Atmospheric Pressure CO2 and Charge-Containing Thiourea Catalysts.

Cycloadditions of epoxides with CO2 to synthesize cyclic five-membered ring organic carbonates are of broad interest from a synthetic, environmental, and green chemistry perspective, and the development of effective catalysts for these transformations is an ongoing challenge. A series of eight charge-containing thiourea salts that catalyze these reactions under mild conditions (i.e., 60 °C and atmospheric CO2 pressure) are reported. Substrate scope and mechanistic studies were also carried out, isotope effects were measured, and a reactive intermediate was isolated revealing a surprising pathway in which a thiourea catalyst serves as a nucleophile in the cleavage of the epoxide ring.

Towards an Asymmetric Organocatalytic α-Azidation of ß-Ketoesters.

Detailed investigations concerning the organocatalytic (asymmetric) α-azidation of prochiral ß-ketoesters were carried out. It was shown that the racemic version of such a reaction can either be carried out under oxidative conditions using TMSN3 as the azide-source with quaternary ammonium iodides as the catalysts, or by using hypervalent iodine-based electrophilic azide-transfer reagents with different organocatalysts. In addition, the latter strategy could also be carried out with modest enantioselectivities when using simple cinchona alkaloid catalysts, albeit with relatively low yields.

Chiral phase-transfer catalysis in the asymmetric α-heterofunctionalization of prochiral nucleophiles.

Chiral phase-transfer catalysis is one of the major catalytic principles in asymmetric catalysis. A broad variety of different catalysts and their use for challenging applications have been reported over the last decades. Besides asymmetric C-C bond forming reactions the use of chiral phase-transfer catalysts for enantioselective α-heterofunctionalization reactions of prochiral nucleophiles became one of the most important field of application of this catalytic principle. Based on several highly spectacular recent reports, we thus wish to discuss some of the most important achievements in this field within the context of this review.

Towards an asymmetric organocatalytic α-cyanation of ß-ketoesters.

This communication describes the first proof of concept for an asymmetric α-cyanation of ß-ketoesters using a hypervalent iodine-based electrophilic cyanide-transfer reagent. A series of different organocatalysts has been investigated and it was found that the use of naturally occurring Cinchona alkaloids allows obtaining the target products in good yields and with moderate enantioselectivities up to er = 76:24 under operationally simple conditions.

Stereoselective Syntheses of Masked ß-Amino Acid Containing Phthalides.

We herein report a protocol for the asymmetric aldol-initiated cascade addition of isoxazolidin-5-ones to ortho-cyanobenzaldehydes by using Takemoto's bifunctional organocatalyst. This approach allows for the synthesis of various novel ß2,2-amino acid-phthalide conjugates with good enantio- and diastereoselectivities in reasonable yields and the further ring-opening of these compounds to acyclic carboxylic acid derivatives was demonstrated too.

Chelation-assisted C-C bond activation of biphenylene by gold(i) halides.

A chelation-assisted oxidative addition of gold(i) into the C-C bond of biphenylene is reported here. The presence of a coordinating group (pyridine, phosphine) in the biphenylene unit enabled the use of readily available gold(i) halide precursors providing a new, straightforward entry towards cyclometalated (N^C^C)- and (P^C)-gold(iii) complexes. Our study, combining spectroscopic and crystallographic data with DFT calculations, showcases the importance of neighboring, weakly coordinating groups towards the successful activation of strained C-C bonds by gold.

Quaternary ß2,2-amino acid derivatives by asymmetric addition of isoxazolidin-5-ones to para-quinone methides.

The highly enantioselective (>99.5% ee) synthesis of a new class of densely functionalized ß2,2-amino acid derivatives by reacting isoxazolidin-5-ones with para-quinone methides in the presence of chiral ammonium salt phase-transfer catalysts was developed. The reaction proceeds with exceptionally low catalyst loadings down to 20 ppm on gram scale and the utilization of the primary addition products towards further manipulations was demonstrated for selected examples.