Super-bases

Potassium, Pubidium, and Cesium idjdrides. Although all the other alkah metal hydrides have been synthesized and some of the properties measured, only potassium hydride [7693-26-7] is commercially available. KH is manufactured in small amounts and sold as a mineral oil dispersion. It is a stronger base than NaH and is used to make the strong reducing agent KBH(C2H )2 and the super bases RNHK and ROK (6). 

Gas-phase basity and proton affinity values for 3,4,6,7,8,9-hexahydro-2/f-pyrido[l,2-n]pyrimidine were determined and they were compared to other super bases, including its lower and higher piperidine ring homologs (94JP0725, 01JPO25). 

Schlosser s super base 615 f. Schmidt trichloroacetimidate glyco-sidation 528,531,537,556 Schwartz s reagent 606, 616 scopadulcic acid A 571 scopadulcic acid diterpenes 569 secocorrin 100, 122, 126 f., 130... 

Solid super bases, prepared by successive treatment of y-alumina with alkali metal hydroxide and alkali metal, are highly active catalysts for reactions involving reactive carbanions, and have been commercialised by Sumitomo (Suzukamo et al, 1997). For example, t.vobutylbenzene, the. starting material for ibuprofen (see earlier) is produced by side-chain alkylation of toluene with propylene over a K/KOH/AI2O3 catalyst (Eqn. (14)). 

Obviously such super bases are suitable only for reactions of aprotic substrates such as hydrocarbons since the reactive alkali metals will be leached from the surface by reaction with protic molecules. 

Proton affinity in the gas phase and pXa values of strong neutral organic (super)bases in acetonitrile were calculated by DFT at the B3LYP level, among others for 34a (TBD, hppFI) and 34b (MTBD, hppM) <20010L1523>. 

While the significance of the bifunctional Brpnsted base catalysts has been illustrated in the previous sections, few examples rely solely on a Brpnsted base interaction for asymmetric catalysis. However, in the past few decades, a novel catalyst system has emerged as a powerful promoter of chiral transformations. The guanidines have gained the reputation as super bases in organic transformations. 

Comparison of the results for catalytic isomerization of pent-l-ene to trans-pent-2-ene with the basic and one-electron donating properties of the catalysts led to the conclusion that two different reaction mechanisms operate in double bond isomerization reactions (a) an ionic mechanism which involves proton abstraction from the alkene molecule by the super base site (pAia = 37 for pentenes) and (b) a free radical mechanism which involves the abstraction of a hydrogen atom from the alkene by the one-electron donor center (Scheme 39). 

Investigations of the generation of super base sites on alkaline earth metal oxides by doping with alkali metals (246,247,253) led to the inference that when zero-valent alkali metals react with a metal oxide surface, the electron donated by the alkali metal to the oxide lattice resides in a defect site, such as an oxygen vacancy, generating a one-electron donor site (F center) (254,255) (Scheme 40). 

Tanabe, K., and Noyori, R., Super Acids and Super bases, ch. 4. Kodanska Scientific, Tokyo, 1980. 

As seen in Table XIII, the yield of 2-aryl-1-vinylpyrroles depends much on the benzene ring substituent. The sharp decrease in the yield of 4-bromophenyl-l-vinylpyrrole (from 4-bromoacetophenone oxime) is expected it is caused by reaction at the bromine atom with the strong base. No success was attained in an attempt to obtain pyrrole from 4-nitroacetophenone oxime under the conditions studied as a result of instability of the substituent in the super base medium. 

Organic super bases, such as DBU, or l,5-diazabicyclo[4.3.0]non-5-ene (DBN) have also been used as effective promoters in the synthesis of PC from propene... 

Trofimov reaction.1 The reaction of ketoximes with acetylene in the super base KOH/DMSO forms N-vinylpyrroles. An extension is the reaction of the unsaturated ketoxime 1 under the same conditions to form either 2 or 3 as the major product.2... 

Streitwieser et al. [160] and BordweU et al. [161] used the lyate ions of organic solvents such as cyclohexylamine and dimethyl sulfoxide in the determination of the C—H acidity of weak organic carbon acids. Using super base systems such as alkali metal salts of cyclohexylamine [i.e. lithium and cesium cyclohexylamides) [160] and dimethyl sulfoxide (sodium dimsyl) [161] in an excess of these non-HBD solvents, relative acidity scales for weak carbon acids have been established. In this way, values for the ionization of over a thousand Bronsted acids in dimethyl sulfoxide have... 

Scales of gas-phase proton affinities and gas-phase acidities for numerous organic compounds, including super bases and super acids [232], can be found in references [115, 120, 232, 233] for comparisons of gas-phase and solution acidities, see references [124, 234-238]. 

Cyclocondensation of malonyl derived O-acyl hydroxamic acid derivatives 6, in the presence of phosphazene super base P2-r-Bu 7, gave rise to isoxazolone carboxylic esters 8 <03TL7763>. 

Such deprotonations may be achieved with SchEosser s super base , a combinatian of butyllithium wid potassium terf-butoxide. Me,COK (Bu OK). This reagent is even more basic than organolithium species. 

Solid base catalyzed reactions are not as commonly used in synthetic processes as are those reactions promoted by solid acids. While several so-called super bases have been developed, they have not been generally used for the types of reactions... 

The truth is that some fruits proposed as super really aren t, and no claims about antioxidant health benefits from fruits are actually established by science or allowed by regulatory authorities. I m going to expose some misconceptions about this expanding category of superfoods and give you a list of twenty fruits that are actually super based on nutritional facts and scientific criteria. I ll share with you how these twenty superfruits can be easily added to your diet, not just because they are delicious, but also for their nutrient properties—scientifically proved to have the potential for lowering your risk of contracting major diseases. 

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