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481.
Zeitschrift für Physik C Particles and Fields - 相似文献
482.
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Masahiro Ojima Yasuo Oka Takashi Kushida Shigeo Shionoya 《Solid State Communications》1977,24(12):845-848
Luminescence spectra of excitonic molecules in CuCl resonantly created by nano-second dye laser excitation are measured at 4.2 K changing the lenghts of the excited region. The spectra are dominated by stimulated emission. The gain coefficient for the MT line is saturated more easily than that for ML, though the former is larger under unsaturated conditions. These gain characteristics explain well various stimulated emission effects observed. 相似文献
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1,3-Diemthyl(5H,7H)imidazo(4,5-pyrimidine-2,4,6-trithione () was synthesized by the reaction of carbon disulfide with 1,3-dimethyl-4-cyano-5-aminoimidazolidine-2-thione () which was produced by reacting trimethylsilyl cyanide with methyl isothiocyanate followed by methanolysis. An unusual reversible formation of the dimethylamine salt of is also described. 相似文献
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A highly efficient method for the synthesis of 1-azabicyclo[x.y.0]alkane amino acid derivatives and their congeners by means of extremely regioselective cyclohydrocarbonylation (CHC) is described. The CHC reactions are catalyzed by Rh-BIPHEPHOS complex under mild conditions. These CHC reaction processes involve (i) an extremely linear-selective hydroformylation of the terminal alkene moiety of a dehydrodipeptide substrate, (ii) intramolecular condensation to form cyclic N-acyliminium key intermediate, and (iii) the second cyclization through intramolecular nucleophilic addition of a heteoatom nucleophile to the cyclic N-acyliminium moiety to afford the corresponding 1-azabicyclo[x.y.0] system. This consecutive double cyclization process proceeds with extremely high diastereoselectivity in most cases. This method has been successfully applied to the syntheses of 1-azabicyclo[4.4.0], -[5.4.0], and -[4.3.0] systems. The mechanisms of the reactions and the rationale for the observed extremely high diastereoselectivity are presented. This Rh-catalyzed CHC process would serve as a highly efficient and versatile method for the syntheses of a variety of conformationally restrained dipeptides, peptidomimetics, alkaloids, and other biologically active natural or unnatural products. 相似文献
488.
Chiou WH Schoenfelder A Sun L Mann A Ojima I 《The Journal of organic chemistry》2007,72(25):9418-9425
Homologues of kainic acid, a naturally occurring potent glutamate receptor agonist, were designed based on a rigidified pipecolinoglutamic acid structure and can be regarded as homokainoids for their potential activities in the central nervous system. These novel homokainoids in an enantiomerically pure form were synthesized from enantiopure (R)- and (S)-Garner's aldehyde, featuring (i) the highly diastereoselective addition of alkenylcuprates to the acrylate intermediates and (ii) the Rh-catalyzed cyclohydrocarbonylation of homoallylic amine intermediates to construct the functionalized piperidine moiety in the key steps. For the introduction of a substituent at the 4- or 5-position of pipecolinoglutamic acid, a few different strategies were used, which successfully led to the formation of enantiopure homokainoids. 相似文献
489.
Tamura O Takeda K Mita N Sakamoto M Okamoto I Morita N Ishibashi H 《Organic & biomolecular chemistry》2011,9(21):7411-7419
Stereoselective vinylogous Mannich reaction of 2-trimethylsilyloxyfuran with L-gulose-derived chiral nitrones in the presence of a catalytic amount of trimethylsilyl trifluoromethanesulfonate was investigated. The selectivity was strongly influenced by the bulkiness of the C-substituent of the nitrone: for example, C-benzyloxymethyl nitrone afforded four stereoisomers, whereas bulky C-[(4S)-2,2-dimethyl-1,3-dioxolan-4-yl]nitrone gave a single stereoisomer. The latter product was elaborated to afford key synthetic intermediates for polyoxin C and dysiherbaine. 相似文献
490.
In the presence of silica gel or titanium tetrachloride, ketene silyl acetals or ketene silyl thioacetals underwent 1,4-addition with α,β unsaturated aldimines which possess a large triphenylmethyl group at the imino nitrogens followed by reduction with sodium cyanoborohydride to give aminopropylated products, δ-amino esters, in good yields. 相似文献