栗原 崇人

Herein we report a scandium-catalyzed regioselective synthesis of 5-carbonyl-4-hydroxybenzofurans via a phenol-directed intramolecular Friedel-Crafts reaction. This synthetic method was applied for the total synthesis of furanoflavones. Experimental studies and density functional theory calculations suggest that hydrogen bond interactions between the phenolic hydroxy group and the scandium complex realize regioselective intramolecular cyclization.

Abstract Although transition metal-catalyzed reactions have evolved with ligand development, ligand design for palladium-catalyzed photoreactions remains less explored. Here, we report a secondary phosphine oxide ligand bearing a visible-light sensitization moiety and apply it to Pd-catalyzed radical cross-coupling reactions. The tautomeric phosphinous acid coordinates to palladium in situ, allowing for pseudo-intramolecular single-electron transfer between the ligand and palladium. Molecular design of the metal complexes aided by time-dependent density functional theory calculations enables the involvement of allyl radicals from π-allyl palladium(II) complexes, and alkyl and aryl radicals from the corresponding halides and palladium(0) complex. This complex enables radical cross-couplings by ligand-to-Pd(II) and Pd(0)-to-ligand single-electron transfer under visible-light irradiation.

Abstract Unsymmetrical 1,1,2-triacylalkenes were conveniently prepared by the oxidative coupling of 1,3-keto esters with terminal alkynes by employing 4.0 equivalents of inexpensive ceric ammonium nitrate (CAN) as the oxidant in acetonitrile as the solvent at 0 °C. The method is milder than previously reported methods and can be conducted under air, thereby demonstrating its practicality and versatility for preparing these useful building blocks. The reaction is believed to occur by a single-electron-transfer process of the 1,3-keto ester substrate initiated by CAN to generate an α-radical species that quickly adds to the terminal alkyne partner in the reaction. Subsequent oxidation of the resulting vinyl radical by air and CAN then leads to the formation of the triacylalkene product as a mixture of E- and Z-isomers. The reaction was shown to be general, with 27 illustrative examples of the formation of the desired products in up to quantitative yield and with moderate to excellent alkene geometrical selectivities.

Polypyrrole-based polyamides are used as sequence-specific DNA probes. However, their cellular uptake and distribution are affected by several factors and have not been extensively studied in vivo . Here, we generated a series of fluorescence-conjugated polypyrrole compounds and examined their cellular distribution using live zebrafish and cultured human cells. Among the evaluated compounds, Py ₃ -FITC was able to visualize collagen-rich tissues, such as the jaw cartilage, opercle and bulbus arteriosus, in early-stage living zebrafish embryos. Then, we stained cultured human cells with Py ₃ -FITC and found that the staining became more intense as the amount of collagen was increased. In addition, Py ₃ -FITC-stained HR cells, which represent a type of ionocyte on the body surface of living zebrafish embryos. Py ₃ -FITC has low toxicity, and collagen-rich tissues and ionocytes can be visualized when soaked in Py ₃ -FITC solution. Therefore, Py ₃ -FITC may be a useful live imaging tool for detecting changes in collagen-rich tissue and ionocytes, including their mammalian analogues, during both normal development and disease progression.