Compounds proton-active

The use of compounds with activated methylene protons (doubly activated) enables the use of a mild base during the Neber reaction to 277-azirines. Using ketoxime 4-toluenesulfonates of 3-oxocarboxylic esters 539 as starting materials and a catalytic quantity of chiral tertiary base for the reaction, moderate to high enantioselectivity (44-82% ee) was achieved (equation 240). This asymmetric conversion was observed for the three pairs of Cinchona alkaloids (Cinchonine/Cinchonidine, Quinine/Quinidine and Dihydro-quinine/Dihydroquinidine). When the pseudoenantiomers of the alkaloid bases were used, opposite enantioselectivity was observed in the reaction. This fact shows that the absolute configuration of the predominant azirine can be controlled by base selection. 

CH3OH molecules, which is facilitated by the spontaneous hydration of these proton exchanged oxides. Platinum loading enhances the activity for all compounds. Considerable activity has been observed towards 02 evolution from aqueous AgN03, though the activity is much less than that of Ti02. This is attributed to the intercalated Ag4 cations that work probably as recombination centers for electrons and holes. 

Preparation of Poly (propylene ether) Polyols. The polymerization of propylene oxide with zinc hexacyanocobaltate complexes in the presence of proton donors results in the production of low-molecular-weight polymers. Table V shows the variety of types of compounds that have been found to act this way. Since these compounds end up in the polymer chains, it seems reasonable to call them chain initiators. Thus, in essence, each of these compounds is activated by the catalyst to react with propylene oxide to form a hydroxylpropyl derivative. Thereafter, the reaction continues on the same basis, with the proton of the hydroxyl group reacting with further propylene oxide. This sequence is shown here with 1,5-pentanediol as the initiator. The hydroxyl... 

The effectiveness of these anions depends to a large degree on the integrity of the jl-X linkage. The p,-NH2 compound is air and moisture stable and exhibits a particularly strong bridge, possibly by virtue of four N-H- F hydrogen bonds between ortho fluorine atoms and the amido NH protons. Activation of common metallocenes with the trityl salt... 

Protic solvents or the addition of proton-active compounds after oxaphosphetane formation shift the stereoselectivity of the reaction in the direction of the ( )-form. If the Wittig reaction is carried out in C2HsOD or if the oxaphosphetane solution, prepared at —75 °C in an aprotic solvent, is treated with deuterated ethanol, then deuterium is incorporated in high yield into the ( )-olefm formed, and the degree of deuterium labelling of the coexisting (Z)-olefin is lower. On the basis of these findings the mechanism discussed below has been established (Scheme 5). 

In these compounds the carbon atom is mostly negative and the phosphorus is positive polarized, thus in the case of an addition of proton-active reagents such as hydrogen halides, alcohols, or amines the proton moves to the carbon and the anionic part moves to the phosphorus atom [Eq. (12)] (8,14). 

Another way of producing a low proton activity at the amalgam surface is to add a suitable polar, aprotic compound to the medium. Suitable compounds include urea and its derivatives, amides, lactams, sulfoxides, and sulfones, such as 1,3-dimethylurea, ethyle-neurea, biuret, formamide, A-methyl formamide, acetamide, 5-butyrolactam, dimethyl sulfoxide, di- -butyl sulfoxide, and dimethyl sulfone [41,42]. Dimethylformamide (DMF) or acetonitrile, besides some of the compounds just mentioned, may be used as solvents [43,44]. One function of the added compound is to establish an aprotic reaction layer at the amalgam surface by selective adsorption of the compound on the amalgam another is to solvate the ion pair (consisting of the radical ion and the cation) in a suitable way. 

Friedel-Crafts acylation usually involves the reaction of an acyl halide, a Lewis acid catalyst, and the aromatic reactant. Several species may function as the active electrophile, depending on the reactivity of the aromatic compound. For activated aromatics, the active electrophile can be a discrete positively charged acylium ion or a complex formed between the acyl halide and the Lewis acid catalyst. For benzene and less reactive aromatics, it is believed that the active electrophile is a protonated acylium ion or an acyiium ion complexed by a Lewis acid. Reactions using acylium salts are slow with toluene or benzene as the reactant and do not proceed with chlorobenzene. The addition of triflic acid accelerates the reactions with benzene and toluene and permits reaction with chlorobenzene. These results suggest that a protonation step must be involved. 

Hydroxyalkylation occurs when certain compounds containing active protons are treated with higher aldehydes e.g., the copper chelate of glycine reacting with aldehydes affords -amino-/ -hydroxy acids 693,694... 

Whereas these reactions of dihalides with proton-active compounds seem reasonably simple, [Mo(NO)(Me2pzb)l2] reacts with Mc2CO, MeEtCO or diacetone alcohol in complex fashion, affording some [Mo(NO)(M pzb)I(OEt)J but also some [ Mo(NO)(Me2pzb)I 20], presumably via a reduced species such as the paramagnetic Mo(NO)(Me2pzb)I. The possible reaction course has been discussed, and it has been established that the dinuclear species has a slightly bent MoOMo system [171.0(15)°], with linear ZMoNO (176(3), mean). Mo—N = 1.74(3) and N—0 = 1.21(4) A (mean values). The two molybdenum coordination shells are eclipsed with respect to each other. 

Theoretical Study of the Proton Affinities of Some Substituted Derivatives of Histamine and Homologous Compounds. Structure-Activity Relationships... 

Theoretical study of the proton affinities of some substituted derivatives of histamine and homologous compounds. Structure-activity relationships... 

This reaction was initially reported by Eisleb in 1941. It is the alkylation of compounds of active hydrogen with alkyl halide via the treatment of sodium amide. The compounds with active hydrogens include deoxybenzoin, diphenylmethane, phenylacetonitrile, fluorene, " benzyl phenyl sulfone, and 2-pyridyl acetonitrile. This reaction normally gives a satisfactory yield of introducing A/, A/ -dialkylamino alkyl group to compounds with an active proton. ... 

This reaction was first reported by Mitsunobu in 1967. It is the alkylation of compounds with active protons by using primary or secondary alcohols as the alkylating agents in combination with triphenylphosphine and diethyl azodicarboxylate (DEAD) or diisopropyl azodicarboxylate (DIAD), to form molecules like esters, ethers, thioethers, and amines. Therefore, this reaction is generally known as the Mitsunobu reaction or Mitsunobu coupling. In addition, the specific reaction for forming esters by means of DEAD (or DIAD) and PPhs is generally referred to as the Mitsunobu esterification." Occasionally, the Mitsunobu reaction is also called the Mitsunobu transformation (for the conversion of alcohol into amines) or Mitsunobu cyclizafion (for the formation of cyclic compounds). Because of its intrinsic features of stereospecificity, as well as its occurrence in neutral media and at room temperature without a prerequisite activation of alcohol, this reaction has been extensively studied and used to synthesize a variety of compounds since 1970. 

Proton-activating groups such as nitrile, ester, or p-nitrophenyl, on carbon atom 5 of the 7r-(penteno-4-lactonyl)cobalt tricarbonyl complexes make the compounds reactive toward bases. Bases cause the elimination of cobalt tricarbonyl anion and 5-substituted 2,4-pentadieno-4-lactones are produced 17). 

If an acid is chosen with a concentration of 1 mol L then the result is a NHE (with N for normali.e., molar for a monoacid). However, it does not quite constitute a SHE because the real compounds are not close to their standard state. For example, the proton activity of an acid with a concentration equal to 1 mol is not equal to 1. The value of the NHE potential is about 6 mV/sHE at room temperature for hydrogen chloride. In practice, if one wishes to have a hydrogen electrode with a potential as close as possible to that of the SHE, then an acidic solution is implemented with a concentration slightly higher than 1 mol L Using this type of electrode is a difficult task and must be reserved to particular applications indeed, many particular experimental precautions are necessary for ensuring an equilibrium state in such a system. 

The reductive coupling of carbonyl compounds with active metals (Na, Mg, Al) yields pinacols. An electron transfer from the metal surface to the carbonyl oxygen (ketyl formation), a soft-soft interaction, is undoubtedly involved. The conversion of esters to acyloins (22, 23) on the surface of metallic sodium is well known. Here the enediolate products can be trapped in situ by Me3SiCl (24). The chlorosilane does not interfere with the coupling, yet it effectively removes the alkoxide ions and neutralizes the enediolate ions immediately on formation. The elimination of RO is imperative, for otherwise Claisen or Dieckmann condensations would compete with the normal course of reaction. These complicating processes require a hard base (e.g. RO ) to abstract a proton from the starting esters, whereas the desired coupling is accomplished by a soft base which is the electrons on the metal surface. 

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