Search

We have synthesized a cyan fluorescent boron complex based on a tridentate imidazo[1,5-a]pyridine ligand. The boron complex was found to have potential applications as not only a chiroptical material but also a heavy-atom-free mitochondria-targeted photosensitizer for cancer treatment.

Herein, we present the first study on the polyaddition reaction of biscarbodiimides with chiral diamines, which focuses on a definite case using optically active trans-4a,8a-decahydroquinoxaline and 1,4-phenylenebis(arylcarbodiimide)s, which readily react with each other under ambient and catalyst-free conditions. The specific reactivity allows for facile access to not only the corresponding chiral polyguanidines under balanced stoichiometry but also their oligomeric analogues under imbalanced stoichiometry via a step-by-step procedure. Spectroscopic, chromatographic, and computational characterization of the novel molecular chains containing arrayed guanidines have revealed their structural, optical, and conformational properties as well as the mechanism of polymerization assisted by molecular association. Their potential use as asymmetric catalysts is also described.

N5-Modified alloxazinium salts including 5-ethyl-1,3-dimethylalloxazinium and 5-ethyl-1,3-dimethyl-8-(trifluoromethyl)alloxazinium salts were readily prepared as alloxazinium-resins from the corresponding N5-unmodified ingredients via the aerobic oxidation—ion exchange protocol, previously introduced by us for the preparation of isoalloxazine analogues, and their catalysis and reusability in H2O2 oxidations were evaluated.

Nucleophilic addition reactions of soft carbon nucleophiles to nitrones in a flow microreactor are reported for the first time. Under microflow conditions at 30 °C to 0 °C, a range of nitrones can be efficiently transformed into the corresponding oxyiminium ions by reacting with either acyl halides or trialkylsilyl triflates, which can subsequently undergo the addition of nucleophiles including allyltributylstannane, ketene methyl tert-butyldimethylsilyl acetal, and N-silyl ketene imines to afford the corresponding adducts in high yields, while such reactions at a similar temperature under batch conditions have resulted in lowering the yields due to undesired side reactions.

Acid dissociation constants (pKa) of 9 kinds of flavin analogues as molecular catalyst candidates were determined by CZE. Although some of the analogues are instable and degradable under the light-exposure or in alkaline aqueous solutions, the effective electrophoretic mobility of the flavin analogue of interest has been measured with the residual substance. The pKa values of the flavin analogues were analyzed through the changes in the effective electrophoretic mobility with varying pH of the separation buffer. One or two steps pKa values were determined by the analysis. One of the degraded species from the flavin analogues, lumichrome, was also detected in the CZE analysis, and its pKa values were also determined. While coexisting impurities generated over the storage conditions were found in some analogues, the pKa values of the target analogues were successfully determined with the help of the CZE separations. A pressure-assisted CZE was utilized for the determination or the estimation of the pKa values of such analogues as possessing carboxylic acid moiety.

We present that thioacetalization of aldehydes can be induced by blue light irradiation in the presence of a catalytic amount of riboflavin tetraacetate (RFTA) under aerobic conditions. Several control experiments have suggested that the reaction is more likely to be catalyzed by acidic species generated in situ during the light irradiation. We have proposed that single electron transfer from a thiol (RSH) to the excited state of RFTA can take place to give a one-electron oxidized thiol (RSH+•) and the one-electron reduced RFTA (RFTA–•), which can be trapped by molecular oxygen to be stabilized as Brønsted acids including the protonated RFTA–• (RFTAH•). Finally, we have demonstrated that such acidic species can be prepared in advance as a solution and used as Brønsted acid catalysts for not only the thioacetalization but also Mannich-type reactions.

Nitrones are important compounds and are highly useful in many aspects. The first part describes the methods for synthesis of nitrones, which are useful and environmentally friendly. Catalytic oxidations, condensations, and other useful reactions are described. The nitrones thus obtained are key intermediates for the synthesis of biologically important nitrogen compounds. The second part describes the fundamental transformations of nitrones, which will provide the strategies and means for the construction of nitrogen compounds. The reactions with nucleophiles or radicals, C—H functionalization, and various addition reactions are described. The last reactions are particularly important for highly selective carbon—carbon bond formations. 1,3-Dipolar cycloaddition reactions are excluded because the size of the review is limited and excellent reviews have been published in Chem. Rev.