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Volume 54, Issue 7
Displaying 1-10 of 10 articles from this issue
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Takeshi OHKUMA, Ryoji NOYORI1996 Volume 54 Issue 7 Pages 553-563
Published: July 01, 1996
Released on J-STAGE: November 16, 2009
JOURNAL FREE ACCESSEnantioselective reduction of prochiral ketones to optically active secondary alcohols is an important, fundamental subject in synthetic organic chemistry, because the resulting chiral alcohols are versatile building blocks for synthesis of natural or unnatural biological active compounds as well as functional materials. Asymmetric hydrogenation is particularly useful for a large-scale reduction because of the operational simplicity, economical advantage, and environmental consciousness. Enantioselective hydrogenation of simple ketones which have no heteroatoms near carbonyl groups has remained difficult. This review describes the recent development in this area. Certain chiral Ru (II) complexes exhibit an excellent catalytic activity and enantiodifferentiation ability in asymmetric hydrogenation of simple ketones in homogeneous phase.View full abstractDownload PDF (1508K) -
Atsushi ABIKO1996 Volume 54 Issue 7 Pages 564-573
Published: July 01, 1996
Released on J-STAGE: January 28, 2010
JOURNAL FREE ACCESSNew chiral auxiliaries based on the isoxazolidine skeleton have been developed. Characteristic feature of these auxiliaries are : 1) High reactivity for asymmetric alkylations. 2) Acylation of the auxiliary with an acid chloride and an amine, or DCC condensation. 3) One step transformation of the reaction products to the corresponding chiral alcohols, aldehydes and ketones without loss of the stereochemical integrity with the recovery of the auxiliary. Asymmetric alkylation of chiral β-substituted alkanols via their triflates lead to the easy access to the “reduced polypropionate units” as well as the first synthesis of the marine natural product (+) -siphonarienone. Enantiomerically pure axially dissymmetric cyclohexylidene compounds were synthesized using asymmetric Horner-Emmons reaction of the phosphonate derived from the auxilliary.View full abstractDownload PDF (1214K) -
Cycloaddition of o-Quinodimethane and Its Analogs to [60] Fullerene, and Properties of CycloadductsYosuke NAKAMURA, Masumi TAKI, Toshiyuki MINOWA, Jun NISHIMURA1996 Volume 54 Issue 7 Pages 574-579
Published: July 01, 1996
Released on J-STAGE: November 16, 2009
JOURNAL FREE ACCESSSeveral C60-o-quinodimethane adducts having various aromatic rings have been synthesized by the simple thermal reaction of C60 with benzocyclobutene homologues. The electronic and photophysical properties of the adducts were found to be virtually independent of the attached aromatic rings, according to the absorption, fluorescence, and transient absorption spectra. In the adduct possessing an N, N-dimethylaniline (DMA) moiety, however, intramolecular electron transfer from S0 (DMA) to S1 (C60) was observed in benzonitrile, while not in cyclohexane. The regio- and stereoselective synthesis of C60-bisadducts has been successful by the reaction between C60 and the compounds in which two o-quinodimethane precursors were connected by an oligomethylene unit of the suitable length (n=2-5). A new nomenclature of C60 derivatives is also proposed in order to designate such bisadducts.View full abstractDownload PDF (785K) -
Recent Development on Fullerence Chemistry Part 2Takeshi AKASAKA, Shigeru NAGASE, Kaoru KOBAYASHI1996 Volume 54 Issue 7 Pages 580-585
Published: July 01, 1996
Released on J-STAGE: November 16, 2009
JOURNAL FREE ACCESSEncapsulation of one or more metal atoms inside fullerene cages (endohedral metallofullerenes) is one of the most exciting topics in the fullerene science, since it could give rise to new species or materials with novel properties which are unexpected for hollow fullerenes. Recent important progress is marked by the successful isolation and purification of Sc@C82, Y@C82, La@C82, Gd@C82, Laz@C80, and Sc2@C84 in large quantities. It is an interesting challenge to disclose how the properties of hollow fullerenes are modified upon endohedral metal-doping.
Recently, we have clarified the electronic structures and properties of endohedral metallofullerenes based on the theoretical calculations and have undertaken the first exohedral functionalization of metallofullerenes with organosilicon compound which can act as a mechanistic probe to clarify the electronic and chemical character of fullerenes. These successful exohedral derivatizations of endohedral metallofullerenes should open the way to a variety of new chemical entities with novel properties, enriching the chemistry of metallofllerenes.
Here we summarize our recent experimental and theoretical studies of the chemical and electronic features of monometallofullerenes and dimetallofullerenes.View full abstractDownload PDF (860K) -
Diastereoselectivity in Ring-Closure ReactionTakashi TOKOROYAMA1996 Volume 54 Issue 7 Pages 586-595
Published: July 01, 1996
Released on J-STAGE: November 16, 2009
JOURNAL FREE ACCESSPotentiality of diastereofacial selection in ring-closure reaction of the substrate with a stereogenic center in the acyclic chain is discussed in terms of “folding strain stereocontrol”, which implies that the difference between total sums of the strain energy involved in the diastereomeric foldings in the transition state is determinative for the diastereofacial selectivity. Firstly, elucidation of the concept is provided referring to the asymmetric induction in intermolecular reaction and literature examples of remote diastereoselection in the ring-closure are briefly surveyed. Then, an account of our investigation directed to generalization of the concept is described. The diastereoselection in cyclization was studied with regard to the locational relationship of the substituents as well as the other factores in the substrates : alkyl- and oxy-substituted 2- (6'-trimethylsilylhex-4'-enyl) -cyclohex-2-enones and alkyl-substituted ethyl 7-bromo-2-methylheptanoates. In the second substrates, the utilization of the oxy-substitutents as a stereocontrolling group has been explored in connection with a stereoselective synthesis of clerodane diterpenoid. Cyclization reaction of 5-methyl- or 5, 6-dimethyl-8-trimethylsilyloctenals was also studied for the stereoselective synthesis of marine natural products. The folding strain stereocontrol is proved to influence diastereoselectivity of a ring-closure reaction to a greater extent than generally thought and the utility of stereoselective ring construction using this approach is emphasized.View full abstractDownload PDF (1363K) -
Mechanisms for Generating an Excited Molecule in Chemi- and Bioluminescent ReactionsTakashi HIRANO, Mamoru OHASHI1996 Volume 54 Issue 7 Pages 596-606
Published: July 01, 1996
Released on J-STAGE: November 16, 2009
JOURNAL FREE ACCESSThe photoprotein aequorin isolated from the jellyfish Aequorea victoria emits blue light in the presence of Ca2+ with a high quantum yield. Aequorin consists of apoaequorin (apoprotein), coelenterazine, and molecular oxygen. Coelenterazine also has a chemiluminescent reactivity with oxygen. In vivo, the excited energy generated by aequorin is transferred to a green fluorescent protein (GFP), which emits green light after energy transfer. The molecular processes in the jellyfish bioluminescence have been studied for designing a highly efficient luminescent compound and for establishing the supramolecular interaction between coelenterazine and apoaequorin as well as the interaction between aequorin and GFP. This review describes the chemiluminescent reaction mechanism of coelenterazine, the supramolecular structure and the bioluminescent character of aequorin investigated by the use of chemically modified coelenterazines and apoaequorin mutants, and the character of GFP.View full abstractDownload PDF (1543K) -
Taichi USUI, Takeomi MURATA1996 Volume 54 Issue 7 Pages 607-615
Published: July 01, 1996
Released on J-STAGE: November 16, 2009
JOURNAL FREE ACCESSSignificant attentions have been focused on the application of glycosidase-catalyzed transglycosylation for practical synthesis of oligosaccharides involved in glycoconjugates. The enzymatic synthesis has become more practical by the use of several glycosidases available in sufficient quantity. This review describes convenient syntheses of di and trisaccharide units, which are related to molecular recognition, by employing regioselective transgalactosylation, trans-N-acetylglucosaminidation, transfucosylation and transmannosylation. The regioselectivity could be manipulated to some extent by using following techniques : (1) careful selection of enzymes, (2) organic co-solvent system, (3) inclusion complex of acceptor glycoside with cyclodextrin.View full abstractDownload PDF (1242K) -
Yoshimasa HIRAT1996 Volume 54 Issue 7 Pages 616-620
Published: July 01, 1996
Released on J-STAGE: January 28, 2010
JOURNAL FREE ACCESSDownload PDF (593K) -
Yoshiro FURUKAWA, Naoya KASAI1996 Volume 54 Issue 7 Pages 621-622
Published: July 01, 1996
Released on J-STAGE: November 16, 2009
JOURNAL FREE ACCESS -
[in Japanese], [in Japanese], [in Japanese], [in Japanese], [in Japane ...1996 Volume 54 Issue 7 Pages 623
Published: July 01, 1996
Released on J-STAGE: November 16, 2009
JOURNAL FREE ACCESSDownload PDF (184K)
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