Selective catalytic reduction direct synthesis

A series of 8-amlnopurine nucleosides and their N -substituted derivatives were prepared via direct brominatlon of the natural purine ribosides and deoxyribosides and subsequent nucleophilic displacement of the 8-bromo group with hydrazine or azide (followed by catalytic reduction), hydroxylamine or allqrlamines . A new synthesis of 2-fluoro-adenoslne was developed, starting from 2,6-diazido-9-(tri-0-acetyl-p-D-ribofuranosyl)purine which was reduced to the 2-amlno-adenosine derivati the latter was selectively diazotized in the presence of fluoroboric acid 2. 2-Fluoro-3 -deoxyadenpsine was prepared from the unprotected 2-amlno-3 -deoxyadenosine in an analogous manner . 2-Aminoadenosine was also prepared by Raney-nickel catalyzed reduction of 2,6-dihydroxylamino-... 

Among various methods to synthesize nanometer-sized particles [1-3], the liquid-phase reduction method as the novel synthesis method of metallic nanoparticles is one of the easiest procedures, since nanoparticles can be directly obtained from various precursor compounds soluble in a solvent [4], It has been reported that the synthesis of Ni nanoparticles with a diameter from 5 to lOnm and an amorphous-like structure by using this method and the promotion effect of Zn addition to Ni nanoparticles on the catalytic activity for 1-octene hydrogenation [4]. However, unsupported particles were found rather unstable because of its high surface activity to cause tremendous aggregation [5]. In order to solve this problem, their selective deposition onto support particles, such as metal oxides, has been investigated, and also their catalytic activities have been studied. 

Because of the pure performance of traditional Cu catalysts in the hydrogenation of C02, efforts have been made to find new, more effective catalysts for direct C02 hydrogenation. The problem is to improve selectivity, specifically, to find catalysts that display high selectivity toward methanol formation and, at the same time, show low selectivity in the reverse water-gas shift reaction, that is, in the formation of CO. It appears that copper is the metal of choice for methanol synthesis from C02 provided suitable promoters may be added. Special synthesis methods have also been described for the preparation of traditional three-component Cu catalysts (Cu-ZnO-A1203 and Cu-Zn0-Cr203) to improve catalytic performance for C02 reduction. 

The combination of the chromatographic separation of enan-tiopure p-hydroxysulfoximine diastereomers and reductive elimination results in a method of ketone methylenation with optical resolution. The technique is illustrated in the synthesis of the ginseng sesquiterpene (—)-p-panasinsene and its enantiomer (eq 5). The addition of the enantiopure lithiosulfoximine to prochiral enones or the diastereoface selective addition to racemic enones results in the formation of two diastereomeric adducts. The hydroxy group in these adducts can be used to direct the Simmons-Smith cyclopropanation (eq 6 and eq 7). Catalytic osmylation of such adducts is directed by the anti effect of the hydroxy augmented by chelation by the methylimino group (eq 7). ... 

The carbonylation of aryl halides with alcohols and amines catalysed by palladium complexes with triphenylphosphine ligand is the convergent and direct route to the synthesis of aromatic esters as well as aromatic amides. Even though these palladium complexes are widely employed as the best catalytic system, those catalysts are difficult to separate and reuse for the reaction without further processing. The major drawbacks are oxidation of triphenylphosphine to phosphine oxide, reduction of palladium complex to metal and termination of the catalytic cycle. The phosphine-free, thermally stable and air resistant catalyst (1) containing a carbon-palladium covalent bond (Figure 12.3) has been found to be a highly selective and efficient catalyst for the carbonylation of aryl iodides.[1]... 

The formation of C—N bonds is an important transformation in organic synthesis, as the amine functionality is found in numerous natural products and plays a key role in many biologically active compounds [1]. Standard catalytic methods to produce C—N bonds involve functional group manipulations, such as reductive amination of carbonyl compounds [2], addition of nucleophiles to imines [3], hydrogenation of enamides [4—8], hydroamination of olefins [9] or a C—N coupling reaction [10, 11]. Recently, the direct and selective introduction of a nitrogen atom into a C—H bond via a metal nitrene intermediate has appeared as an attractive alternative approach for the formation of C—N bonds [12-24]. 

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