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The Taft's substituent constant of the pentafluorophenyl group is reestimated to be 1.50 by correlation between IR spectral data and sigma constants for a series of esters of 3-phenylpropanic acid and butanoic acid. The pentafluorophenyl group is found to possess the moderate electron-withdrawing ability between 3,5-dinitrophenyl and difluoromethyl groups.

Research has been conducted on zinc porphyrin and 5-[4-(1-hydroxyethyl)phenyl]-10,15,20-triphenylporphyrin. The validity of the transition-state model proposed for the lipase-catalyzed secondary alcohol kinetic resolution has been investigated via the synthesis of these porphyrin compounds and the results are reported.

The synthesis of optically pure and active 1,2-bis(pentafluorophenyl)ethane-1,2-diols (1R,2R) and (1S,2S) using lipase-catalyzed transesterification derived cyanohydrin intermediates (R)- and (S)- is described. X-ray structural data of the naproxen ester of the intermediates indicate that they exhibit well-ordered packing structure with pentafluorophenyl and the 6-methoxynaphthyl groups exhibiting face-to-face stacking interactions and end-to-end parallel contacts.

An NADPH-dependent reductase that exhibit reducing activity for 1-chloro-2-hexanone was isolated from bakers' yeast. Gel filtration and sodium dodecyl sulphate-polyacrylamide gel electrophoresis indicated that the reductase is a monomeric enzyme with a 37-kilodalton molecular weight. Moreover, the reductase exhibited low Michaelis values and high specificity constants for all the substrates investigated.

The acyl moiety of acylating agents enhances the enantioselectivity of Pseudomonas cepacia lipase-promoted acylations of racemic alcohols. This stereochemical controlling function, which arises from the transient attachment of the acyl group at the active site of the lipase, was evident in the kinetic resolution of 2-((N,N-dimethylcarbamoyl)-methyl)-3-cyclopenten-1-ol and 2-(2-(tert-butyldimethylsilyloxy)ethyl)-3-cyclopenten-1-ol using enol esters as acyl donors.

Host-guest combination influences the circular dichroism (CD) spectra of amino acid ester-porphyrin supramolecular systems. Observation of induced CD requires the presence of intermolecular hydrogen bonding to the carbonyl group of the guest molecule. Molecular orbital calculations show the influence of relative geometry or the carbonyl group and porphyrin plane on the induced CD of the system. Coupling of electric and magnetic transition dipole moments of the carbonyl group with the electric transition dipole moment of the porphyrin Soret bond influences the observed induced CD.

A chiral porphyrin and its reference porphyrins with features for binding of alpha-amino acid esters to hosts are synthesized. Three recognition groups, Zn, OH, and CH2CO2Me, are introduced into the porphyrin framework for binding experiments. Zn ion and the OH group stabilize the host-guest complex through coordination and hydrogen bonding interactions.

Three host porphyrins were prepared in order to investigate the relationship between the structure of the hosts and their recognition of amino acid esters. A host molecule bearing both coordination and hydrogen bonding recognition sites was constructed. Host-guest interactions were characterized by UV-vis titration, circular dichroism (CD) and 1H nuclear magnetic resonance spectroscopic studies. It was found that the fixation of the carbonyl group of the guest by two-point recognition caused marked enhancements in induced CD.

Research has been conducted on the enantioselectivity and substrate specificity of the chiral catalysts. The potential capabilities of the carbonyl reductase, a monomeric NADPH-dependent enzyme, as a chiral biocatalyst have been investigated and the results are reported.

Chiral macrocycles with the hydrogen bond donor/acceptor sites in the cavity are prepared and covalently bonded to silica gel to provide chiral stationary phases (CSPs), which has displayed excellent abilities to solve chiral compounds including ketones, esters, carboxylic acids, sulfoxides, amines amino acid derivatives and metal complexes. The MM calculations have shown that the chiral recognition of Co[(acac).sub.2] is obtained by a combination of steric interactions and hydrogen bonds between the carbonyl O atom coordinated to the Co atom and the macrocyclic amide NH groups.

The size and shape of the chiral cavity of a macrocyclic receptor are tuned by the alteration of the binaphthyl moiety in order to improve the chiral recognition/discrimination ability. The host with the 3,5-bis(trifluoromethyl)phenyl group at the 3,3'-positions has an excellent ability as an NMR chiral solvating agent.

Bifunctional macrocycles and diamide are designed and synthesized. The analysis has shown the importance of the relative orientation of the binaphthyl moiety and the orthogonal disposition of the binaphthyl moiety in bifunctional macrocycle has brought the differential ring-current effect on the chiral guest molecule bound.

Optically active aziridine derivatives have attracted considerable attention because of their versatile synthetic utilities, and a variety of methods for asymmetric syntheses are reported. Methods for the regio-and stereoselective ring cleavage of the aziridines are well studied, and are still under active investigation for the syntheses of chiral amines, amino alcohols, and amino acids.

The temperature effect on enantioselectvity (E) in lipase-catalyzed kinetic resolutions of 34-phenyl-2H-azirine-2-methanol was evaluated through the utilization of a lipase from Pseudomonas cepacia (PS) in a reaction with vinyl acetate in ether under -40 degrees Celsius. Lowering the temperature even as to as low as -40 degrees Celsius enhances the E value, favoring the (R)-enantiomer.

Chiral macrocyclesfeaturing sulfonamide and/or amide groups asanion-binding sites were synthesized. X-ray crystal structures andDFT calculations have shown that they adopt different conformationsthat may lead to unique binding behavior. Indeed, various anions couldbe sensed by their colorimetric and/or fluorescence signal output.The chiral macrocycles showed chiral recognition for chiral anions.Furthermore, a multisensor array with two or four chiral receptorsdiscriminated seven phosphate anions (AMP, ADP, ATP, CMP, GMP, Pi,and PPi) with 100% classification accuracy. [ABSTRACT FROM AUTHOR]

A correction to the article "Bifunctional Porphyrin Catalysts for the Synthesis of Cyclic Carbonates from Epoxides and C02: Structural Optimization and Mechanistic Study" in the September 2014 issue is presented.

The most common protocols for the quantitative determination of the enantiomeric excess ( ee) of raw mixtures by ESI-MS reveal inadequate in cases where the distribution of diastereomeric derivatives diverges from the ee of original solutions. This phenomenon is attributable to a matrix effect, i.e., to the stereospecific formation of high order noncovalent adducts in the ESI droplets, which alters the actual availability of the diastereomeric species under MS analysis. In this frame, the assumption of classic protocols that the ionization correction factor q is independent on the composition of the mixture submitted to analysis is questionable. An alternative methodology is presented in this paper, which is aimed at circumventing the problem by excluding any chemical derivatization of the original raw mixture. It is based on the measurement of the actual distribution of ESI-formed proton-bound diastereomeric complexes from the enantiomeric mixture through a careful analysis of their reaction kinetics with a suitable reactant. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

The catalytic reactions of indoles with CO 2 and phenylsilane afforded indolo[3,2- b ]carbazoles, where the fused benzene ring was constructed by forming two C-H bonds and four C-C bonds with two CO 2 molecules via deoxygenative conversions. Nine-membered cyclophanes made up of three indoles and three CO 2 molecules were also obtained, where the cyclophane framework was constructed by forming six C-H bonds and six C-C bonds. These multicomponent cascade reactions giving completely different carbocycles were switched simply by choosing the solvent, acetonitrile or ethyl acetate.

Tetrabutylammonium acetate (TBAA) and Cu(OAc) 2 worked as a binary catalytic system for the solvent-free N -formylation of amines with CO 2 and PhSiH 3 . This catalysis making C-H and C-N bonds with CO 2 was coupled with the C-C bond-forming reactions to achieve the one-pot synthesis of enamines, aldehydes, and nitriles. The X-ray crystal structure of a Cu(OAc) 2 -TBAA complex was also revealed.

Catalytic CO 2 reduction with phenylsilane under solvent-free conditions was linked with the one-pot synthesis of 3,4-dihydropyrans from β-dicarbonyl compounds and styrenes. The synthesis includes three processes: (1) bis(silyl)acetal formation from CO 2 and phenylsilane and a domino reaction of (2) Knoevenagel condensation and (3) inverse-electron-demand oxa-Diels-Alder reaction. The first process was catalyzed by a pentanuclear Zn II complex (0.07 mol %) to generate bis(silyl)acetals, which were hydrolyzed into formaldehyde to be used in the second step.

Attempts were made to minimize the amounts of catalyst and solvent in the NHC-catalyzed benzoin reactions of solid aldehydes. In some case, solid-to-solid conversions proceeded in the solvent-free NHC-catalyzed benzoin reactions. Even if a mixture of the substrate, N -heterocyclic carbene (NHC) precursor, and inorganic base was initially a powdery solid, the reaction did proceed at reaction temperature lower than the melting points of each compound. The solid mixture partially melted or became a slurry or suspension in the meantime. We call this solid/liquid mixture a semisolid state. The reaction giving an optically active product was faster than that giving a racemic mixture of the same product. Melting-point depression was observed for a series of mixtures of the substrate and product in different substrate/product ratios. Solvent-free solid-to-solid conversions were accelerated by the formation of a semisolid state resulting from the melting-point depression of the solid substrate accompanied by the product formation. In the case of solid substrates with high melting points, melting-point depression was useless, and the addition of a small amount of solvent was needed. The first total synthesis of isodarparvinol B was achieved via the NHC-catalyzed intramolecular benzoin reaction using a small amount of solvent as an additive., Competing Interests: The authors declare no competing financial interest., (Copyright © 2020 American Chemical Society.)

A series of pyrenes sandwiched by axially chiral 1,1'-binaphthyls were synthesized. Among them, ( R , R )- 3 possessing 2-hydroxy-3,3'-dimethylbinaphthyls exhibited solvent-dependent inversion of the sign of circularly polarized luminescence (CPL) without a change in emission wavelength. The (-)- and (+)-CPL were detected in nonpolar and polar solvents, respectively, with g lum values of -0.012 and +0.012. This switching property originates from the inversion of excimer chirality caused by the presence or absence of intermolecular hydrogen bonds in the excited state. The CPL intensity was also changed by variation of the temperature and concentration.

A series of axially chiral peri -xanthenoxanthenes (PXXs) were synthesized from 1,1'-bi-2-naphthol without optical resolution. These are the first examples of chiral PXXs. Among them, PXX 5 with two naphthalene rings connected via a methylenedioxy bridge and a chiral axis displayed intense fluorescence (FL) and circularly polarized luminescence (CPL) both in solution (Φ FL of 0.72 and | g lum | of 1.4 × 10 -3 ) and in the solid state (Φ FL of 0.13 and | g lum | of 4.8 × 10 -3 ). The bridged structure of PXX 5 adjusts the angle between the vectors of the electric and magnetic transition dipole moments, which is essential for showing intense CPL activity.

Chiral binaphthyl-strapped Zn(II) porphyrins with triazolium halide units were synthesized as bifunctional catalysts for kinetic resolution of epoxides with CO 2 . Several catalysts were screened by changing the linker length and nucleophilic counteranions, and the optimized catalyst accelerated the enantioselective reaction at ambient temperature to produce optically active cyclic carbonates and epoxides.

Hemisquaramide tweezers, a new family of H-bond donor organocatalysts, are reported. The catalysts could be synthesized within two steps. Among them, H 8 -binaphthyl-linked hemisquaramide 7 markedly accelerated the synthesis of cyclic carbonates from epoxides and CO 2 . The reactions proceeded well under mild and solvent-free conditions. Kinetic resolution was also achieved at -20 °C ( s = 3.0). The adjustable bite angle and orientation of the two NH groups of the catalysts are important for the high activity.

A series of chiral cyclic dyads, axially chiral binaphthyls linked to a 3,3'-bipyridyl, was synthesized. The dyad 2 bearing methoxy groups exhibited ON/OFF properties in circularly polarized luminescence (CPL), yielding a | g lum | of 1.6 × 10 -3 or 0 without any change in fluorescence. This type of CPL switch is unprecedented. Regioisomer 4 exhibited a dextro/ levo rotation switching ability in [α] D . X-ray structures as well as experimental and theoretical analyses suggested that the switching properties depended on conformational changes.

Among chiral macrocycles 1 synthesized, 1m with the 3,5-bis(trifluoromethyl)phenylethynyl group was the best organocatalyst for the enantioselective synthesis of cyclic carbonates from disubstituted or monosubstituted epoxides and CO 2 . The X-ray crystal structure of 1m revealed a well-defined chiral cavity with multiple hydrogen-bonding sites that is suitable for the enantioselective activation of epoxides. A catalytic cycle proposed was supported by DFT calculations.

The Glaser coupling reaction of ethynyl-substituted carbazole-based isophlorins provided butadiyne-bridged dimers, which were transformed into the thiophene-bridged dimers via the annulation reaction. Oxidation of these isophlorin dimers afforded carbazole-based diporphyrins. Notable electronic interactions in the diporphyrins have been confirmed by means of UV/vis-near-infrared (NIR) absorption spectroscopy, cyclic voltammetry (CV) measurements, and density functional theory (DFT) calculations.

The intermolecular or intramolecular asymmetric benzoin reaction was catalyzed by a small amount of N-heterocyclic carbene (NHC) (0.2-1 mol %) under solvent-free conditions. The solvent-free intramolecular asymmetric Stetter reaction also proceeded efficiently with NHC (0.2-1 mol %). In some cases, even solid-to-solid or solid-to-liquid conversions took place with low catalyst loading (0.2-1 mol %).

Carbazole-based BODIPYs were synthesized in three steps using an organometallic approach consisting of sequential Ir-catalyzed borylation, Suzuki-Miyaura coupling, and boron complexation. Various substituents were introduced into the carbazole moiety, and large substituent effects were confirmed by means of absorption spectroscopy, cyclic voltammetry, and DFT calculations. Dibenzocarbazoles were also converted into the corresponding BODIPYs.

We prepared bifunctional Mg(II) porphyrin catalysts 1 for the solvent-free synthesis of cyclic carbonates from epoxides and CO2. The activities of 1d, 1h, and 1i, which have Br(-), Cl(-), and I(-) counteranions, respectively, increased in the order 1i < 1h < 1d. Catalysts 1d and 1j-m, which bear four tetraalkylammonium bromide groups with different alkyl chain lengths, showed comparable but slightly different activities. Based on the excellent catalyst 1d, we synthesized Mg(II) porphyrin 1o with eight tetraalkylammonium bromide groups, which showed even higher catalytic activity (turnover number, 138,000; turnover frequency, 19,000 h(-1)). The catalytic mechanism was studied by using 1d. The yields were nearly constant at initial CO2 pressures in the 1-6 MPa range, suggesting that CO2 was not involved in the rate-determining step in this pressure range. No reaction proceeded in supercritical CO2, probably because the epoxide (into which the catalyst dissolved) dissolved in and was diluted by the supercritical CO2. Experiments with (18)O-labeled CO2 and D-labeled epoxide suggested that the catalytic cycle involved initial nucleophilic attack of Br(-) on the less hindered side of the epoxide to generate an oxyanion, which underwent CO2 insertion to afford a CO2 adduct; subsequent intramolecular ring closure formed the cyclic carbonate and regenerated the catalyst. Density functional theory calculations gave results consistent with the experimental results, revealing that the quaternary ammonium cation underwent conformational changes that stabilized various anionic species generated during the catalytic cycle. The high activity of 1d and 1o was due to the cooperative action of the Mg(II) and Br(-) and a conformational change (induced-fit) of the quaternary ammonium cation.

Bifunctional organocatalysts bearing an ammonium betaine framework have been developed as a new catalytic motif for the activation of carbon dioxide and epoxides to produce cyclic carbonates.

Bicyclic tertiary alcohols 1 bearing quaternary stereocenters at the two adjacent bridgehead positions were synthesized with high stereoselectivity via the intramolecular crossed benzoin reactions catalyzed by NHC organocatalysts.

Chiral macrocycles with the hydrogen bond donor/acceptor sites in the cavity were synthesized and covalently bonded to silica gel to give chiral stationary phases (CSPs), which showed excellent abilities to resolve various chiral compounds, such as benzoin and Co(acac)3, in HPLC. Various organic solvents could be used as the mobile phase to optimize the resolution efficiency of CSPs, and in some cases, even MeCN, MeOH, and CO(2) could be used for the complete resolution of enantiomers.

[structure: see text] Bifunctional macrocycle 1 with C2 symmetry was newly synthesized. NMR studies demonstrated that receptor 1 functions as a chiral shift reagent (solvating agent) that is highly effective for a wide range of chiral compounds having a carboxylic acid, oxazolidinone, lactone, alcohol, sulfoxide, sulfoximine, isocyanate, or epoxide functionality. Binding constants were determined to investigate the binding behavior of 1.

[reaction: see text] We have found new conditions for the Suzuki-Miyaura coupling reaction applicable to pentafluorophenylboronic acid (C(6)F(5)B(OH)(2)) (1), which is an inactive substrate under normal conditions. The reactions of 1 with phenyl iodide or bromide under Pd(PPh(3))(4)/CsF/Ag(2)O or Pd(2)(dba)(3)/P(t-Bu)(3)/CsF/Ag(2)O catalytic system conditions gave 2,3,4,5,6-pentafluoro-1,1'-biphenyl (3a) in more than 90% yields. Combination of CsF and Ag(2)O was essential for promoting these reactions.

A new type of chiral receptor (R,R)- or (S,S)-1b with C(2) symmetry was synthesized. An induced-fit type of binding behavior of 1b for diamines was revealed by CD spectroscopy. NMR studies demonstrated that 1b can function as a highly sensitive chiral shift reagent for the determination of the enantiomeric purity of chiral diamines, aziridine, and isoxazoline at the microgram level. [structure: see text]