Improved conditions for the asymmetric synthesis of α-amino acids using Cinchona-derived anthracenylmethyl ammonium salts as chiral phase-transfer organocatalysts

Cinchonidine and cinchonine-derived monomeric anthracenylmethyl ammonium salts bearing different counter-anions are used as chiral organocatalysts in the enantioselective alkylation of a benzophenone-imine tert-butyl glycinate under phase-transfer conditions. Generally, an improvement of the enantioselectivity is observed when the counterions are tetrafluoroborate and hexafluorophosphate using 50% aqueous KOH as the base and toluene/chloroform as the solvent. The enantioselectivities achieved are comparable and frequently higher, even working under simpler and less-strict reaction conditions and with lower organocatalyst loading, than those reported previously.     

A 2-Calabi–Yau realization of finite-type cluster algebras with universal coefficients

Mathematische Zeitschrift - We categorify various finite-type cluster algebras with coefficients using completed orbit categories associated to Frobenius categories. Namely, the Frobenius...     

On Frobenius (Completed) Orbit Categories

Let ?? be a Frobenius category, \({\mathcal P}\) its subcategory of projective objects and F : ?? → ?? an exact automorphism. We prove that there is a fully faithful functor from the orbit category ??/F into \(\operatorname {gpr}({\mathcal P}/F)\), the category of finitely-generated Gorenstein-projective modules over \({\mathcal P}/F\). We give sufficient conditions to ensure that the essential image of ??/F is an extension-closed subcategory of \(\operatorname {gpr}({\mathcal P}/F)\). If ?? is in addition Krull-Schmidt, we give sufficient conditions to ensure that the completed orbit category \({\mathcal E} \ \widehat {\!\! /} F\) is a Krull-Schmidt Frobenius category. Finally, we apply our results on completed orbit categories to the context of Nakajima categories associated to Dynkin quivers and sketch applications to cluster algebras.     

Recoverable (R)- and (S)-binap-Ag(I) complexes for the enantioselective 1,3-dipolar cycloaddition reaction of azomethine ylides

The first enantioselective 1,3-dipolar cycloaddition reaction of amino acid derived azomethine ylides and maleimides catalyzed by very stable and recyclable chiral (R)- or (S)-binap-AgClO(4) complexes is described. The reactions are performed at room temperature, in good yields, with high endo diastereoselectivity and enantioselectivity, the complex being recovered by simple filtration.     

Infrared Spectroscopic Evidence for a Heterogeneous Reaction between Ozone and Sodium Oleate at the Gas–Aerosol Interface: Effect of Relative Humidity

The heterogeneous ozonolysis of sodium oleate aerosols in an aerosol flow tube is reported under different relative humidity (RH%) conditions. Submicron sodium oleate particles were exposed to a known ozone concentration and the consumption of sodium oleate was monitored by infrared spectroscopy. When the experimental results are treated as a surface‐mediated reaction (i.e., following a Langmuir–Hinshelwood type mechanism), the following parameters are obtained: at low RH%, = (3 ± 1) × 10^?16 cm³ molecule^?1 and = (0.046 ± 0.006) s^?1; at high RH%, = (6 ± 2) × 10^?16 cm³ molecule^?1 and = (0.21 ± 0.05) s^?1. From these pseudo–first‐order coefficients, the reactive uptake coefficients for dry and aqueous sodium oleate aerosols are calculated as (1.5 ? 0.5) × 10^?7 and (1.7 ? 0.7) × 10^?6, respectively. Hydrated oleate aerosols display both an increase in the ozone trapping ability and an increase in the effective rate reaction at the droplet surface compared to dry aerosol surfaces. These observations may provide an explanation for some of the variability observed between lab studies of dry ozonolysis and real‐world, atmospheric lifetimes of oleic acid–related species.     

Strongly Emissive and Photostable Four‐Coordinate Organoboron N,C Chelates and Their Use in Fluorescence Microscopy

Six strongly fluorescent four‐coordinate organoboron N,C chelates containing an aryl isoquinoline skeleton were prepared. Remarkably, the fluorescence quantum yields reach values of up to 0.74 in oxygen‐free toluene. The strong B?N interaction was corroborated by the single‐crystal X‐ray analysis of two dyes. The intramolecular charge‐transfer character of the fluorophores was evidenced by solvatochromism studies and time‐dependent DFT calculations at the PCM(toluene)/CAM‐B3LYP/6‐311++G(2d,p)//PCM(toluene)/B3LYP/6‐311G(2d,p) level of theory. The compounds combine high chemical stability with high photostability, especially when equipped with electron‐donating substituents. The strong fluorescence and the large Stokes shifts predestine these compounds for use in confocal fluorescence microscopy. This was demonstrated for the imaging of the N13 mouse microglial cell line. Moreover, significant two‐photon absorption cross sections (up to 61 GM) allow the use of excitation wavelengths in the near‐infrared region (>800 nm).     

Recent advances in Sonogashira reactions

The coupling of aryl or vinyl halides with terminal acetylenes catalysed by palladium and other transition metals, commonly termed as Sonogashira cross-coupling reaction, is one of the most important and widely used sp(2)-sp carbon-carbon bond formation reactions in organic synthesis, frequently employed in the synthesis of natural products, biologically active molecules, heterocycles, molecular electronics, dendrimers and conjugated polymers or nanostructures. This critical review focuses on developments in the Sonogashira reaction achieved in recent years concerning catalysts, reaction conditions and substrates (352 references).     

Fluorinated alcohols as promoters for the metal-free direct substitution reaction of allylic alcohols with nitrogenated, silylated, and carbon nucleophiles

The direct allylic substitution reaction using allylic alcohols in 1,1,1,3,3,3-hexafluoroisopropanol (HFIP) and 2,2,2-trifluoroethanol (TFE) as reaction media is described. The developed procedure is simple, works under mild conditions (rt, 50 and 70 °C), and proves to be very general, since different nitrogenated nucleophiles and carbon nucleophiles can be used achieving high yields, especially when HFIP is employed as solvent and aromatic allylic alcohols are the substrates. Thus, sulfonamides, carbamates, carboxamides, and amines can be successfully employed as nitrogen-based nucleophiles. Likewise, silylated nucleophiles such as trimethylsilylazide, allyltrimethylsilane, trimethylsilane, and trimethylsilylphenylacetylene give the corresponding allylic substitution products in high yields. Good results for the Friedel-Crafts adducts are also achieved with aromatic compounds (phenol, anisole, indole, and anilines) as nucleophiles. Particularly interesting are the results obtained with electron-rich anilines, which can behave as nitrogenated or carbon nucleophiles depending on their electronic properties and the solvent employed. In addition, 1,3-dicarbonyl compounds (acetylacetone and Meldrum's acid) are also successfully employed as soft carbon nucleophiles. Studies for mechanism elucidation are also reported, pointing toward the existence of carbocationic intermediates and two working reaction pathways for the obtention of the allylic substitution product.     

Enantioselective direct aldol reaction of α-keto esters catalyzed by (S(a))-binam-D-prolinamide under quasi solvent-free conditions

(S(a))-Binam-D-prolinamide (20 mol%), instead of (S(a))-binam-L-prolinamide, in combination with chloroacetic acid (100 mol%) is an efficient organocatalyst for the direct aldol reaction between α-keto esters as electrophiles and alkyl and α-functionalised ketones, under quasi solvent-free conditions, providing access to highly functionalised chiral quaternary γ-keto α-hydroxyesters with up to 92% ee.