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Although helicenes are promising molecules, the synthetic difficulty and tediousness have often been problems, and only small amounts of optically pure helicenes have been obtained by using chiral HPLC in most cases. Herein, aza[7]helicenes or closed‐aza[7]helicenes with (1R)‐menthyl substituents were selectively synthesized via the intramolecular Scholl reaction, and the diastereomeric pairs were separated by silica gel column chromatography. The optically pure helicenes were further transformed into the corresponding cyclic dimers, and the chiroptical properties were investigated. The rigid π‐frameworks of the dimers led to the high molar extinction coefficients and fluorescence quantum yields, while the twisted helicene moieties induced clear Cotton effects and CPL in the visible region, and the high CPL brightness (BCPL) was achieved. Furthermore, the cyclic dimers were found to have the macrocyclic cavity with the two NH groups suitable for the selective binding of a fluoride anion, which induced significantly redshifted fluorescence and CPL in the red region. [ABSTRACT FROM AUTHOR]

D2‐symmetric (R)‐binaphthyl‐bridged pyrenophanes containing thioether bonds were synthesized. The pyrenophanes exhibited the temperature‐induced sign inversion of circularly polarized luminescence (CPL) while maintaining the emission wavelength and reversibility. The Δglum value reached 0.02, and the FL quenching by heat was negligible. The sign inversion of CPL originates from the inversion of intramolecular excimer chirality associated with excitation dynamics. The two pyrenes form a kinetically trapped left‐handed twist excimer at low temperatures, while they form a thermodynamically favored right‐handed twist excimer at high temperatures. The thioether linkers can impart flexibility suitable for the inversion of chirality of the excimers. [ABSTRACT FROM AUTHOR]

Circularly polarized luminescence (CPL) dyes are recognized to be new generation materials and have been actively developed. Molecular recognition systems provide nice approaches to novel CPL materials, such as stimuli‐responsive switches and chemical sensing materials. CPL may be induced simply by mixing chiral or achiral, luminescent or nonluminescent host and guest; there are several combinations. Molecular recognition can potentially save time and effort to construct well‐ordered chiral structures with noncovalent attractive interactions as compared with the multi‐step synthesis of covalently bonded dyes. It is a challenging subject to engage molecular recognition events with CPL, and it is important and interesting to see how it is achieved. In fact, simple molecular recognition systems can even enable the fine adjustment of CPL performance and detailed conformational/configurational analysis of the excited state. Here we overview the recent achievements of simple host–guest complexes capable of exhibiting CPL, summarizing concisely the host/guest structures, CPL intensities, and characteristics. [ABSTRACT FROM AUTHOR]

BPh3 catalyzes the N‐methylation of secondary amines and the C‐methylenation (methylene‐bridge formation between aromatic rings) of N,N‐dimethylanilines or 1‐methylindoles in the presence of CO2 and PhSiH3; these reactions proceed at 30–40 °C under solvent‐free conditions. In contrast, B(C6F5)3 shows little or no activity. 11B NMR spectra suggested the generation of [HBPh3]−. The detailed mechanism of the BPh3‐catalyzed N‐methylation of N‐methylaniline (1) with CO2 and PhSiH3 was studied by using DFT calculations. BPh3 promotes the conversion of two substrates (N‐methylaniline and CO2) into a zwitterionic carbamate to give three‐component species [Ph(Me)(H)N+CO2−⋅⋅⋅BPh3]. The carbamate and BPh3 act as the nucleophile and Lewis acid, respectively, for the activation of PhSiH3 to generate [HBPh3]−, which is used to produce key CO2‐derived species, such as silyl formate and bis(silyl)acetal, essential for the N‐methylation of 1. DFT calculations also suggested other mechanisms involving water for the generation of [HBPh3]− species. [ABSTRACT FROM AUTHOR]

A series of D2‐symmetric macrocycles composed of alternately linked pyrene and binaphthyl moieties (binaphthyl‐bridged pyrenophanes) have been synthesized. Among them, a pyrenophane possessing ether linkers at the 2,7‐positions of the pyrenes exhibited intense circularly polarized luminescence (CPL) with a |glum| value of 0.053. This value is by far the highest for excimers and was not sensitive to temperature, solvent, or concentration. The CPL originated from a twisting pyrene excimer, with the (R)‐binaphthyl moieties producing a left‐handed twist excimer, which exhibited (−)‐CPL. The electric and magnetic transition dipole moments are perfectly parallel, which is the best relationship for strong CPL. [ABSTRACT FROM AUTHOR]

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.

BPh3 catalyzed the N-methylation of secondary amines and the C-methylenation (methylene-bridge formation between aromatic rings) of N,N-dimethylanilines or 1-methylindoles in the presence of CO2 (1 atm) and PhSiH3 without solvent at 30–40 °C. A cascade reaction from 1-methyl-2-oxindole to 3,3′-methylenebis(1-methylindole) via 1-methylindole also proceeded. [ABSTRACT FROM AUTHOR]

RutheniumII complexes bearing three axially chiral bipyridyl ligands were synthesized as a new family of chiral complex dyes, and Δ‐(S)‐ and Λ‐(S)‐diastereomers were obtained. The X‐ray crystal structure analyses, spectroscopy, and DFT calculations suggested that all the bipyridyls maintained chirality in both the ground and excited states, and the Δ‐(S)‐ and Λ‐(S)‐isomers are the matched (more relaxed) and mismatched (more constrained) pairs, respectively. The mismatched Λ‐(S)‐isomer exhibited red circularly polarized phosphorescence (CPP) both in solution and in the solid state. The solution state CPP is the most intense of ruthenium complexes, while the solid state CPP is the first example of them. It is supposed that, for the Λ‐(S)‐isomer, the six cumulative CH/π interactions suppress further distortion in the T1 state. [ABSTRACT FROM AUTHOR]

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.

Carbazole‐based aza[7]helicenes and hetero[9]helicenes were successfully obtained via the intramolecular Scholl reaction of 3,6‐bis(biphenyl‐2‐yl)carbazole congeners, while the reaction of 3,6‐bis(naphthylphenyl)‐appended carbazole gave a triple helicene via an unexpected simultaneous double aryl rearrangement. DFT calculations suggested that the rearrangement proceeded via an arenium cation intermediate. In addition, the reaction of methoxy‐appended substrate gave an azahepta[8]circulene via the concurrent C−C bond formation. These helical dyes showed circularly polarized luminescence. The azahepta[8]circulene was further transformed into deeply saddle‐distorted dibenzodiaza[8]circulenes as the first example of its solution‐based synthesis and unambiguous structural determination. [ABSTRACT FROM AUTHOR]

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.

The one-step C-methylenation of anilines and indoles with CO2 and phenylsilane was catalyzed by a pentanuclear ZnII complex to give diarylmethanes via geminal C–H and C–C bond formation. It is proposed that the zinc–hydride complex generated in situ is a catalytically active species and that bis(silyl)acetal is a key intermediate. When aniline was used as a substrate, both the C-methylenation and N-methylation proceeded. [ABSTRACT FROM AUTHOR]

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.

A series of axially chiral 1,1′‐binaphthyls with trialkylsiloxy (OSiR3) groups were synthesized. Among them, 1 a–c possessing OSiR3 groups at the 7,7′‐positions and methyl groups at the 2,2′‐positions were liquids at room temperature, and the neat liquids showed circularly polarized luminescence (CPL) (R=Bu; Φfl,liquid=0.21, |glum,liquid|=1.6×10−3). The |glum,liquid| value is the highest of pure liquids. These compounds remained liquid over a broad range of temperatures, down to −50 °C. Time‐dependent DFT calculations indicated that in the excited state, the binaphthyls adopt a transoid conformation with a small angle between the electric and magnetic transition dipole moments (θμ,m=77°), which is a key factor in their CPL activity. The best binaphthyl dihedral angle in the excited state is approximately 110°. [ABSTRACT FROM AUTHOR]

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.

Directly linked carbazole-based core-modified diporphyrin D2 and fused diporphyrin F2 were synthesized. These diporphyrins showed significant electronic interactions and conjugation allowing for redshifted near infrared (NIR) absorption and small HOMO–LUMO gaps as confirmed by NIR absorption spectroscopy, cyclic voltammetry (CV) measurements, and DFT calculations. [ABSTRACT FROM AUTHOR]

A variety of carbazolyl‐appended Schiff bases were readily synthesized from 1‐formylcarbazoles and aniline derivatives. Boron complexation of the resulting ligands allowed for facile preparation of new carbazole‐based BODIPY analogues showing solid‐state fluorescence. Furthermore, some dyes were converted into chiral compounds through the Et2AlCl‐mediated incorporation of a binaphthyl unit. The chiral dyes showed aggregation‐induced fluorescence and circularly polarized luminescence (CPL) with the ΦF and glum of up to 0.22 and −3.5×10−3, respectively, in the solid state. The solid‐state fluorescence and CPL were well characterized by the crystal packing analyses and DFT calculations. [ABSTRACT FROM AUTHOR]

Carbon dioxide (CO2) was used as a C1 source to prepare silyl formates, formamides, and aldehydes. Tetrabutylammonium acetate (TBAA) catalyzed the solvent-free N-formylation of amines with CO2 and hydrosilane to give formamides including Weinreb formamide, Me(MeO)NCHO, which was successively converted into aldehydes by one-pot reactions with Grignard reagents. [ABSTRACT FROM AUTHOR]

Helical carbazole‐based BODIPY analogues were readily synthesized via aza[7]helicenes. The structures of azahelicene‐incorporated BF2 dyes were elucidated by x‐ray diffraction analysis. DFT calculations revealed that the π‐conjugated system expanded from the helicene moiety to the BODIPY framework. The azahelicene‐fused boron complexes showed the Cotton effects and the circularly polarized luminescence (CPL) in the visible region. Furthermore, an axially chiral binaphthyl group was attached to the helically chiral dyes, which enhanced the chiroptical properties. [ABSTRACT FROM AUTHOR]

A series of carbazole‐based boron dipyrromethenes (BODIPYs) 2 a–g bearing binaphthyl units have been synthesized by the Et2AlCl‐mediated reaction of the corresponding BODIPY difluorides 1 a–g with 1,1′‐binaphthalene‐2,2′‐diol. Substituents such as halogen, nitrile, and amino groups were tolerated under the reaction conditions, and the reaction of the phenylethynyl‐substituted 1 h gave (R,R)‐3 h bearing two binaphthyl units. The chiroptical properties of these dyes with different substituents were investigated by UV/Vis, CD, fluorescence, and circularly polarized luminescence (CPL) spectroscopy. The CD spectra showed Cotton effects in the absorption region of the BODIPY moieties. In addition, they showed CPL both in solution and in the solid state. Interestingly, several dyes recorded higher glum values in the solid state, probably due to intermolecular interactions. Because (R,R)‐3 h recorded relatively low glum values, the diastereomer (R,S)‐3 h was prepared. The (R,S) diastereomer showed intense CPL, which suggests a synergetic effect of the two binaphthyl groups. Finally, chiral carbazole‐based BODIPY dimers have been synthesized for the first time and their chiroptical properties were investigated. They showed redshifted fluorescence and CPL, which reached the near‐IR (NIR) region in the solid state. [ABSTRACT FROM AUTHOR]