Ethanol exchange reactions

The key step in the total synthesis of rhizobitoxine is the Pd-catalyzed exchange reaction of the methyl alkenyl ether moiety in 4 with the functionalized alcohol, although the yield is low[3]. The enol pyruvate 6 (a-ethoxyacrylic acid) is prepared by the reaction of methyl a-methoxyacrylate or a-methoxy-acrylic acid (5) with ethanol catalyzed by PdCl2(PhCN)2 at room temperature in the presence of CuCli and NaH2P04[4],... 

Selectivity in formation of protective groups may also be achieved by a proper choice of reaction conditions and catalyst. Thus formation of the 3-monothioketal from 3,6-diketones is achieved by dilution of the ethane-dithiol-boron trifluoride reaction mixture with acetic acid. 3-Monocyanohydrins are obtained in good yield from 3,20-diketo-(5a)-pregnanes by diluting the exchange reaction with ethanol. Similarly, dilution of the... 

An exchange reaction of 9 at the remaining hydroxyl group with the carbamate of ethanol affords carisoprodol (10)... 

The first extensive kinetic study of these reactions was carried out by Ingold et a/.7I3b, who demonstrated that for the two-alkyl exchange reaction, i.e. the reverse direction of equilibrium (283), the kinetics in acetone and ethanol were cleanly second-order, viz. 

As an example consider the exchange reaction between benzyl iodide and free iodide ions, Eq. (3-43).6 Mixing ethanolic solutions of benzyl iodide and radio-labeled potassium iodide started the isotopic exchange. At different times, samples were withdrawn and added to a benzene-water mixture, causing separation into two layers. The aqueous layer contained the iodide ions, and the organic layer contained the benzyl iodide. The activity of 1311 was determined in each layer. 

Dynamic polymeric systems utilizing the C=N exchange reaction have been reported by Lehn s group. They have suggested a polymerization system consisting of a fluorene-based dialdehyde monomer 4, cyclohexane diamine 5, and fluorene-based diamine 6 as a comonomer (Scheme 8.2) [20,21]. In principle, a 1 1 1 mixture of all monomers in ethanol was expected to yield the two-component polymers 7 and 8 together with all component-mixed polymers. However, polymer 7 was dominantly yielded (80%) due to the nucleophilicity of diamines. The nucleophilic-ity of aliphatic diaminocyclohexane is much higher than that of aromatic... 

Ligand exchange reactions starting from [Re(NPh)Cl3(PPh3)2] and excess maltol in ethanol in the presence of triethylamine give a dark green solution from which the diamagnetic complex... 

However, the hemiaminal 17 is unstable as a free base and readily undergoes exchange reactions. Since the hydroxy moiety of 17 is more easily displaced than the amine moiety, a highly reactive cyclopropyliminium salt 18 is formed, which then reacts with weak nucleophiles such as ethanol, to give e. g., 19. Otherwise in water solution 17 can also probably eliminate ammonia to form the highly reactive cyclopropanone 20, which is in equilibrium with its hydrate 21 and hemi-acetal 22, Eq. (8) [20]. It has been reported that hydrate 21 is also a potent inhibitor of ALDH [20,21]. 

Amine-Exchange Reactions. Procedure A. A solution of a copper compound was heated in 10 ml. of n-butylamine or aniline on a steam bath, and, after 30 minutes, the mixture was poured into water. The crystals which formed were filtered off and recrystallizea from 95% ethanol. 

U(OEt)5 is easily prepared by oxidation of U(OEt)4 by bromine in ethanol, followed by addition of the calculated quantity of sodium ethoxide, a reaction which yields181 only Np(OEt)4Br in the case of Np(OEt)4. U(OEt)s is commonly used as the starting material for the preparation of other uranium(V) alkoxides by alcohol exchange reactions. A comprehensive review of metal alkoxides includes a useful discussion of the uranium(V) compounds.182... 

In ethanol solution, tertiary phosphines react with [MoCl4(NCEt)2] to yield mer-[MoOCl2(PR3)3], which can undergo exchange reactions to give mer-[MoOX2(PR3)3] (X = Br,... 

The complications which result from the hydrolysis of alkali metal cyanides in aqueous media may be avoided by the use of non-aqueous solvents. The one most often employed is liquid ammonia, in which derivatives of some of the lanthanides and of titanium(III) may be obtained from the metal halides and cyanide.13 By addition of potassium as reductant, complexes of cobalt(O), nickel(O), titanium(II) and titanium(III) may be prepared and a complex of zirconium(0) has been obtained in a remarkable disproportion of zirconium(III) into zirconium(IV) and zirconium(0).14 Other solvents which have been shown to be suitable for halide-cyanide exchange reactions include ethanol, methanol, tetrahydrofuran, dimethyl sulfoxide and dimethylformamide. With their aid, species of different stoichiometry from those isolated from aqueous media can sometimes be made [Hg(CN)3], for example, is obtained as its cesium salt form CsF, KCN and Hg(CN)2 in ethanol.15... 

The H-D exchange reaction of 3-ethoxybutanoate in ethanol-rf (which occurs with a diastereomeric excess of 82%) has been modelled by performing ab initio calculations on protonation of the enolate of 3-fluorobutanoic acid by HCN the predicted diastereomeric excess (84-91%) is dependent on die level of dieory used but similar for botii cis and trans enolates.140 For each diastereomeric padiway die C—F bond is... 

The exchange reactions of organyltrialkoxysilanes with THEA mostly require heating of the components in an appropriate inert solvent (benzene, toluene, xylene, anisole, chloroform, methanol, ethanol etc.) for a long time. However, in some cases the reactions can be carried out at room temperature or, if necessary, with cooling. The transetherification rates and silatrane yields increase in the presence of an alkali metal hydroxide or alkoxide as a basic catalyst. 

The most widely used method for nucleophilic iodination is the Cu+-assisted method, which was first described by Mertens et al [5]. This method can be used in a bromine for radioiodine or an iodine for radioiodine exchange reaction, and results in a regiospecific substitution (scheme 3). A limitation of this labelling method is that it has to be performed in water. If the substrate however is insoluble in water, a mixture of 10% ethanol in water is also possible, higher concentrations of ethanol lead to the precipitation of reagents. It is therefore difficult to iodinate lipophilic compounds with this method. 

The treatment of 3-chloro-4//-pyrido[ 1,2-a]pyrimidin-4-one 619 with sodium phenolate in boiling ethanol yielded 2-methylimidazo[l, 2-a]pyrimi-dine 620 instead of the chloro-to-phenoxy exchange reaction (83H1083). 

Diazotization in the presence of sulfuric add affords a simple means of avoiding the exchange reaction since diazonium add sulfates do not rearrange. Thus, by treating the diazonium add sulfate of tribromoaniline with boiling ethanol, pure tribromobenzene is obtained in about 80% yield.29 Even pentabromoaniline suffers no loss of bromine when deaminated via the diazonium add sulfate.32... 

Exchange reactions using triorgano telluronium halides as starting materials produced triorgano telluronium salts with the anions Y identified below. These telluronium salts precipitate when aqueous or ethanolic solutions of the reactants are combined. 

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