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71.
72.
Kuwano R Kashiwabara M Ohsumi M Kusano H 《Journal of the American Chemical Society》2008,130(3):808-809
Catalytic asymmetric hydrogenation of N-Boc-protected pyrroles proceeded with high enantioselectivity by using a ruthenium catalyst modified with a trans-chelating chiral bisphosphine PhTRAP. The ruthenium catalyst prepared from Ru(eta3-methallyl)2(cod) and (S,S)-(R,R)-PhTRAP in the presence of triethylamine was the most enantioselective for the asymmetric hydrogenation of methyl pyrrole-2-carboxylate, giving the desired (S)-proline derivative with 79% ee in 92% yield. Moreover, 2,3,5-trisubstituted pyrroles bearing a large substituent at the 5-position were hydrogenated with 93-99.7% ee. The asymmetric reduction of 4,5-dimethylpyrrole-2-carboxylate gave only all-cis isomer and created three chiral centers with high degree of stereocontrol in a single process. This is the first highly enantioselective reduction of pyrroles. 相似文献
73.
Two-dimensional growth of GaN thin films on an atomically flat C-face 6H-SiC(0001) surface prepared by ultra-high vacuum Si-etching is observed when using an AlN buffer layer in N plasma-assisted molecular beam epitaxy. Scanning tunneling microscopy and reflection high energy electron diffraction observations reveal a series of Ga-stabilized reconstructions which are consistent with those reported for an N-polar GaN(0001) film. The result, including the effect observed previously for GaN thin film on Si-terminated 6H-SiC(0001), agrees with the polarity assignment of heteroepitaxial wurtzite GaN films on polar 6H-SiC substrates, i.e., GaN film grown on SiC(0001) is <0001> oriented (N-face) while that on SiC(0001) is <0001> oriented (Ga-face). 相似文献
74.
Satoshi Ueno Dr. Ryosuke Shimizu Ryoichi Kuwano Prof. 《Angewandte Chemie (International ed. in English)》2009,48(25):4543-4545
Gone fishing : When propiophenone and related ethyl ketones are treated with morpholine in the presence of K3PO4, chlorobenzene, and [Ni(cod)2]/PMe3 catalyst, a carbon–nitrogen bond is formed selectively at the β position (see scheme; cod=cycloocta‐1,5‐diene). Secondary amines were employed as substrates to give the corresponding β‐enaminones.
75.
Asymmetric Hydrogenation of Azaindoles: Chemo‐ and Enantioselective Reduction of Fused Aromatic Ring Systems Consisting of Two Heteroarenes 下载免费PDF全文
Dr. Yusuke Makida Masahiro Saita Takahiro Kuramoto Dr. Kentaro Ishizuka Prof. Dr. Ryoichi Kuwano 《Angewandte Chemie (International ed. in English)》2016,55(39):11859-11862
High enantioselectivity was achieved for the hydrogenation of azaindoles by using the chiral catalyst, which was prepared from [Ru(η3‐methallyl)2(cod)] and a trans‐chelating bis(phosphine) ligand (PhTRAP). The dearomative reaction exclusively occurred on the five‐membered ring, thus giving the corresponding azaindolines with up to 97:3 enantiomer ratio. 相似文献
76.
Kitazawa M Ishitsuka Y Kobayashi M Nakano T Iwasaki K Sakamoto K Arakane K Suzuki T Kligman LH 《Photochemistry and photobiology》2005,81(4):970-974
The generation of reactive oxygen species (ROS) by ultraviolet radiation (UVR) accelerates skin aging, which is known as photoaging. Because cutaneous iron catalyzes ROS generation, sequestering iron by chelating agents is thought to be an effective approach toward preventing photoaging. Previously, N-(4-pyridoxylmethylene)-l-serine (PYSer) was designed as an antioxidant to suppress iron-catalyzed ROS generation by its iron-sequestering activity. In this study, PYSer showed protective effects against skin damage in hairless mice irradiated with ultraviolet B (UV-B). Topical application of PYSer to the skin significantly delayed and/or decreased the visible wrinkle formation induced by chronic UV-B irradiation. A histological study indicated that UV-B-induced epidermal hypertrophy and lymphocytic infiltration were suppressed by PYSer. Moreover, PYSer showed suppressive activity against the UV-B-induced increase in glycosaminoglycans (GAG). These results indicate that PYSer is a promising antioxidant for the prevention of chronic skin photoaging by its iron-sequestering activity. 相似文献
77.
78.
An experiment was designed to investigate the effects of sound level (LA), number of single noises (N), level of total energy (LT) and mean energy level () on the noisiness of steady state and intermittent noises. With the level and duration of pink noise controlled with a sound system called “Programmable Sound Control System”, 16 kinds of intermittent noises and 22 kinds of steady state noises were prepared. Seven subjects judged the noisiness of these stimuli by magnitude estimation. Their judgments were converted into the corresponding sound level (point of subjective equality, abbreviated PSE) by using the power function obtained between sound level and magnitude estimation for the seven kinds of steady state noises. As a result, the level of total energy and mean energy level were found inappropriate to evaluate the noisiness of intermittent noises though they showed high correlation with the noisiness of steady state noises. PSE's of the intermittent noises showed good correspondence with LN, which is expressed by the equation . LN could also be applied to steady state noises if it was assumed that a steady state noise with a duration of DT is equal to a 2000 ms noise presented times. This result suggests that LN is a good measure of the noisiness of both steady state and intermittent noises. 相似文献
79.
Depending on the N-heterocyclic carbene catalyst utilized, α-unbranched aldehydes selectively provided amides, esters, or carboxylic acids through oxidation by NCS. The α-unbranched aldehyde underwent these reactions chemoselectively in the presence of an aromatic or α-branched aldehyde. 相似文献
80.