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371.
Nicolaou KC Pihko PM Bernal F Frederick MO Qian W Uesaka N Diedrichs N Hinrichs J Koftis TV Loizidou E Petrovic G Rodriquez M Sarlah D Zou N 《Journal of the American Chemical Society》2006,128(7):2244-2257
Syntheses of the three key building blocks (65, 98, and 100) required for the total synthesis of the proposed structure of azaspiracid-1 (1a) are described. Key steps include a TMSOTf-induced ring-closing cascade to form the ABC rings of tetracycle 65, a neodymium-catalyzed internal aminal formation for the construction of intermediate 98, and a Nozaki-Hiyama-Kishi coupling to assemble the required carbon chain of fragment 100. The synthesized fragments, obtained stereoselectively in both their enantiomeric forms, were expected to allow for the construction of all four stereoisomers proposed as possible structures of azaspiracid-1 (1a-d), thus allowing the determination of both the relative and absolute stereochemistry of the natural product. 相似文献
372.
Rosica Petrova Nikolova Keiko Fujiwara Noriaki Nakayama Vladislav Kostov-Kytin 《Solid State Sciences》2009,11(2):382-388
The small-pore zirconosilicate Na2ZrSi2O7·H2O crystallizes in monoclinic system with space group C2/c, a = 5.4715(4); b = 9.4111(6); c = 13.0969(8) Å, β = 92.851(7)°. Its framework consists of layers built of ZrO6 octahedra and SiO4 tetrahedra and forming condensed [Si2O7] pyrogroups by connection. The sodium ions and water molecules are placed in channels set up between the layers. The stoichiometric and structural similarities of the studied phase with anhydrous compounds having general chemical formula A2(3)MT2O7 (A = Na,K; M = Zr,Lu,Sc; T = Si,Ge) are discussed. The topological relationship of their structures is interpreted in the light of spatial combination of silicon and zirconium polyhedra as basic building units into larger composite building units and their three-dimensional arrangement. 相似文献
373.
Kenji Hayashi Minoru Hirayama Taizo Muta Noriaki Seto Takeshi Shirafuji 《Fortschritte der Physik》1967,15(10):625-660
A review is given of recent developments in compositeness arguments of particles in the framework of Lagrangian field theory and S-matrix theory. 相似文献
374.
Optical Review - Recently, smartphone cameras have been increasingly used to take pictures of documents. When a shadow appears in the captured document image, it causes problems such as reduced... 相似文献
375.
Akiya Ogawa Noriaki Takami Masahito Sekiguchi Noboru Sonoda Toshikazu Hirao 《Heteroatom Chemistry》1998,9(6):581-584
Elemental sulfur can be reduced to the corresponding thiolate anion species (S2− and S2−2) selectively by samarium diiodide in the presence and absence of HMPA, respectively. The subsequent alkylation of the thiolate anion species provides a useful synthetic route to dialkyl sulfides and disulfides. © 1998 John Wiley & Sons, Inc. Heteroatom Chem 9: 581–584, 1998 相似文献
376.
Toshifumi Satoh Tomoko Imai Yoshikazu Kitajyo Takahiro Maeda Atsushi Narumi Harumi Kaga Noriaki Kaneko Toyoji Kakuchi 《Macromolecular Symposia》2004,217(1):39-46
The thermally induced cationic polymerizations of 1,6-anhydro-β-D -glucopyranose ( 1a ), 1,6-anhydro-β-D -mannopyranose ( 1b ) and 1,6-anhydro-β-D -galactopyranose ( 1c ) as a latent cyclic AB4-type monomer were carried out using (S-2-butenyl)tetramethylenesulfonium hexafluoroantimonate ( 2 ) as an initiator. The solution polymerization in propylene carbonate proceeded without gelation to produce the water-soluble hyperbranched polysaccharides ( 3a-c ) with controlled molecular weights and narrow polydispersities. The degree of branching (DB), estimated by the methylation analysis of 3a-c , was in the range of 0.38 – 0.49. The thermally induced cationic polymerization of 1a-c using 2 is a facile method leading to a hyperbranched polysaccharide with a high DB value. 相似文献