Acceptor-catalyst method

Obtained copoly and block-copolyestersulfoneketones, as well as polyaiylates based of dichloranhydrides of phthalic acids and chloranhy-dride of 3,5-dibromine- -oxybenzoic acid and copolyester with groups of terephthaloyl-bis(w-oxybenzoic) acid possess high mechanical and dielectric properties, thermal and fire resistance and also the chemical stability. The regularities of acceptor-catalyst method of polycondensation and high-temperature polycondensation when synthesizing named polymers have been studied and the relations between the composition, structure and properties of polymers obtained have been established. The synthesized here block-copolyesters and copolyesters can find application in various fields of modem industry (automobile, radioelectronic, electrotechnique, avia, electronic, chemical and others) as thermal resistant constmction and layered (film) materials. 

Peters and van Bekkum noted that the original method of Sakurai and Tanabe suffered from problems due to the competitive reduction of the A A -dimethylaniline. In their modified procedure, diisopro-pylethylamine is used as HCl acceptor/catalyst regulator, and 10% palladium on carbon as catalyst. As for the Sukarai-Tanabe procedure, the reaction is carried out at room temperature and atmospheric pressure in acetone or ethyl acetate. In the latter solvent, which is said to be marginally preferable, the reduction is complete within minutes for aliphatic acyl chlorides, although aromatic substrates may take several days. 

The synthesis is lead via the method of acceptor-catalyst polycondensation. The double exeess of triethylamine in respect to oligoketones is used as acceptor-catalyst. Obtained block-copolyketones possess good solubility in chlorinated organic solvents and can be used as temperature-resistant high-strength durable constructional materials. 

The method of acceptor-catalyst polyetherification can be used to produce [184, 185] thermo-reactive polyarylenesulfones on the basis of nonsaturated 4,4 -dioxy-3,3 -diallylbisphenyl-2,2 -propane and various chlor- and sulfo- containing monomers and oligomers. The set of physic-mechanical properties of polymers obtained allows one to propose them as constructional polymers, sealing coatings, film materials capable of operating under the influence of aggressive environments and high temperatures. 

Metallic Pd is a good catalyst for the conversion of the primary azide 34 into the nitrile 35 in the presence of a hydrogen acceptor such as diphenylacety-lene[33]. By this method, organic halides can be converted into nitriles without increasing the carbon number. Reaction of the azidoformate 36 with an allylic... 

The l ,J -DBFOX/Ph-transition metal aqua complex catalysts should be suitable for the further applications to conjugate addition reactions of carbon nucleophiles [90-92]. What we challenged is the double activation method as a new methodology of catalyzed asymmetric reactions. Therein donor and acceptor molecules are both activated by achiral Lewis amines and chiral Lewis acids, respectively the chiral Lewis acid catalysts used in this reaction are J ,J -DBFOX/Ph-transition metal aqua complexes. 

We employed malononitrile and l-crotonoyl-3,5-dimethylpyrazole as donor and acceptor molecules, respectively. We have found that this reaction at room temperature in chloroform can be effectively catalyzed by the J ,J -DBFOX/Ph-nick-el(II) and -zinc(II) complexes in the absence of Lewis bases leading to l-(4,4-dicya-no-3-methylbutanoyl)-3,5-dimethylpyrazole in a good chemical yield and enantio-selectivity (Scheme 7.47). However, copper(II), iron(II), and titanium complexes were not effective at all, either the catalytic activity or the enantioselectivity being not sufficient. With the J ,J -DBFOX/Ph-nickel(II) aqua complex in hand as the most reactive catalyst, we then investigated the double activation method by using this catalyst. 

Asymmetric conjugate addition of lithium amides to alkenoates has been one of the most powerful methods for the synthesis of chiral 3-aminoalkanoates. High stereochemical controls have been achieved by using either chiral acceptors as A-enoyl derivatives of oxazolidinones (Scheme 4) 7 7a-8 chiral lithium amides (Schemes 5 and 6),9-12 or chiral catalysts.13,14... 

Since the first use of catalyzed hydrogen transfer, speculations about, and studies on, the mechanism(s) involved have been extensively published. Especially in recent years, several investigations have been conducted to elucidate the reaction pathways, and with better analytical methods and computational chemistry the catalytic cycles of many systems have now been clarified. The mechanism of transfer hydrogenations depends on the metal used and on the substrate. Here, attention is focused on the mechanisms of hydrogen transfer reactions with the most frequently used catalysts. Two main mechanisms can be distinguished (i) a direct transfer mechanism by which a hydride is transferred directly from the donor to the acceptor molecule and (ii) an indirect mechanism by which the hydride is transferred from the donor to the acceptor molecule via a metal hydride intermediate (Scheme 20.3). 

The requirements for new glycosylation methods outlined at the beginning of this chapter, namely convenient diastereocontrolled anomeric O-ac-tivation (first step) and subsequent efficient diasterecontrolled glycosylation promoted by genuinely catalytic amounts of a catalyst (second step), are essentially completely fulfilled by the trichloroacetimidate method. This is clearly shown by the many examples and references given in this article. In terms of stability, reactivity, and applicability toward different acceptors, the... 

The oxidation of substituted pyridines to iV-oxides was reported by Sharpless and coworkers to proceed with yields between 78 and 99% (Scheme 154). A variety of substituents like electron donor as well as acceptor groups and alkenyl substituents are tolerated. In 1998, Sharpless and coworkers reported an alternative method for the preparation of pyridine-A-oxides in which the MTO/H2O2 catalyst could be replaced by cheaper inorganic rhenium derivatives (ReOs, Re207, HOReOs) in the presence of bis(trimethylsilyl) peroxide (equation 73). Yields of the prepared A-oxides after simple workup (filtration and bulb to bulb distillation) ranged from 70-98%. Molecular sieves slowed down the reaction while small amounts of water (0-15%) were essential for the reaction. Both electron-poor or electron-rich pyridines give high yields of their A-oxides and while para-... 

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