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251.
Direct reductive amination (DRA) using triethylsilane (TESH) and catalytic bismuth(III) chloride (BiCl3) is described for the first time. The use of TESH and BiCl3 provides easy handling, low cost, non-toxicity, and a mild Lewis acid activity, thereby meeting the demand for green and sustainable chemistry. The developed DRA is highly chemoselective and applicable to less-basic amines. The experimental results of this study revealed that the developed DRA could be catalyzed by BiCl3, which was gradually reduced to Bi(0) or bismuth with a low valency by TESH, but TESCl, Bi(0), and Bi(0) with TESCl catalyzed the DRA to some extent. 相似文献
252.
Mie KodaniAyumi Takamori Kazuo TakimiyaYoshio Aso Tetsuo Otsubo 《Journal of solid state chemistry》2002,168(2):582-589
Seven conductive radical cation salts based on MDSe-TSF (methylenediselenotetraselenafulvalene) have been synthesized by electrocrystallization in the presence of Cl−, Br−, I3−, I2Br−, PF6−, ClO4−, and Cu(NCS)2− counter anions. The crystal appearances of these salts fairly depend on the anions employed. X-ray crystallographic analyses have revealed that the PF6 and ClO4 salts in the shape of brown thin plates adopt the θ-type structures characterized by the herringbone arrangement of donor stacks, whereas the Cl and Br salts in the shape of black thick plates favor the κ-type structures with the orthogonal arrangement of donor dimers. Regardless of different crystal appearances or crystal packing patterns, all these salts show high conductivity (>102 S cm−1) at room temperature and retain metallic properties down to 4.2 K. Of them, the Br salt shows a weak but distinct diamagnetic shielding signal below 4 K in the dc magnetization measurement under zero-field-cooled (ZFC) condition, suggesting a sign of superconductivity. The band calculations of both PF6 and Br salts demonstrate closed Fermi surfaces indicative of two-dimensional molecular conductors. 相似文献
253.
Nanofibrillar cellulose aerogels 总被引:3,自引:0,他引:3
Hao Jin Yoshiharu Nishiyama Masahisa Wada Shigenori Kuga 《Colloids and surfaces. A, Physicochemical and engineering aspects》2004,240(1-3):63-67
Highly porous aerogels consisting of cellulose nanofibrils were prepared by dissolution/regeneration of cellulose in aq. calcium thiocyanate followed by regeneration and carefully controlled drying. The influence of drying method (regular freeze drying, rapid freeze drying, and solvent exchange drying) on resulting porosity was studied by electron microscopy and nitrogen adsorption. While regular freeze drying caused significant coalescence of microfibrillar units, solvent exchange drying gave highly porous aerogel composed of approx. 50 nm-wide cellulose microfibrils. Correspondingly, specific surface area of the solvent-exchange-dried aerogels ranged 160–190 m2/g, in contrast to 70–120 m2/g of regular freeze-dried materials. Rapid freeze technique using liquid nitrogen-cooled metal plate gave aerogel sheets with asymmetrical porosity, with the face contacted by copper having porous structure similar to those of solvent-exchange dried material. 相似文献
254.
N. Otsubo 《manuscripta mathematica》2000,101(1):115-124
Conjecures of Beilinson and Bloch–Kato describe the order of zeros of L-functions of motives in terms of motivic cohomology groups and Selmer groups. We restrict our attention to the parts generated by the cycle classes, and give modest evidence for the conjectures. Received: 7 June 1999 / Revised version: 7 September 1999 相似文献
255.
The highly stereoselective total synthesis of nemorosone via a new approach to the bicyclo[3.3.1]nonane-2,4,9-trione core which features intramolecular cyclopropanation of an α-diazo ketone, stereoselective alkylation at the C8 position, and regioselective ring-opening of cyclopropane is described. The total synthesis of nemorosone includes chemo- and stereoselective hydrogenation directed by the internal alkene. 相似文献
256.
Formal Total Synthesis of (−)‐Taxol through Pd‐Catalyzed Eight‐Membered Carbocyclic Ring Formation 下载免费PDF全文
Sho Hirai Masayuki Utsugi Mitsuhiro Iwamoto Prof. Dr. Masahisa Nakada 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(1):355-359
A formal total synthesis of (?)‐taxol by a convergent approach utilizing Pd‐catalyzed intramolecular alkenylation is described. Formation of the eight‐membered carbocyclic ring has been a problem in the convergent total synthesis of taxol but it was solved by the Pd‐catalyzed intramolecular alkenylation of a methyl ketone affording the cyclized product in excellent yield (97 %), indicating the high efficiency of the Pd‐catalyzed intramolecular alkenylation. Rearrangement of the epoxy benzyl ether through a 1,5‐hydride shift, generating the C3 stereogenic center and subsequently forming the C1–C2 benzylidene, was discovered and utilized in the preparation of a substrate for the Pd‐catalyzed reaction. 相似文献
257.