Methoxide-methanol dimer

Compound 4 was found to react readily with the secondary amine 13 in refluxing acetonitrile to produce the fully protected, mixed dimer 22 (Scheme 4). The monobenzoyl species 23 could be generated by deprotection of the cytosine moiety with sodium methoxide/methanol at room temperature, while one hour at reflux was required to achieve the fully deprotected dinucleotide 1. 

The catalysis afforded by the La3 + system for the transesterifications of paraoxon in ethanol and methanol is quite spectacular relative to the background reactions that are assumed to be promoted by the lyoxide. The reaction rate constant of ethoxide with paraoxon in ethanol at 5.1 x 10-3 dm3 mol-1 s-133 is roughly a factor of two lower than the rate constant of methoxide with paraoxon in methanol (1.1 x 10 2dm3mol 1 s-1).17a However a solution 2mmoldm-3 in total [La3 + ], which contains 1 mmol dm-3 of Lal+, has a maximum rate constant of 7 x 10-4s-1 for decomposition of 1 in ethanol at pH of 7.3, and accelerates the rate of ethanolysis of paraoxon by a factor of 4.4 x 10n-fold relative to the ethoxide reaction at the same pH.34 By way of comparison, the acceleration afforded by a 1 mmol dm-3 solution of the La + dimer catalyzing the methanolysis of 1 at the maximal pH of 8.3 (kobs = 0.0175 s 1) is 109-fold greater than its background methoxide reaction. On this simple basis La2+ in ethanol appears to be catalytically superior to La2+ in methanol, but this stems almost exclusively from the pH values... 

With lower hydrochloric acid concentration and reversal of the mode of addition, i.e., acid to indanone-nitrite mixture, the intermediate 2-methyl-2-nitroso-l-indanone may also be isolated as its dimer. This can be isomerized to the isocarbostyril rapidly in refluxing methanolic sodium methoxide and more slowly in concentrated hydrochloric acid.4... 

This novel anodic methoxyiation may proceed via the fluorosulfonium ion B in a Pummerer-type mechanism as shown in Scheme 6.11. In this mechanism, the cation radical A of the sulfide is trapped by a fluoride ion, and this step should suppress side reactions from the cation radical A (such as dimerization and nucleophilic attack on an aromatic ring) even when deprotonation of A is slow due to the weak electron-withdrawing Rf groups or electron-donating substituents on the benzene ring. Since fluoride ions are much weaker nucleophiles compared to methoxide, it is reasonable that the methoxyiation predominates in methanol. 

Few X-ray diffraction data are available for the organotin alkoxides. Trimethyltin methoxide in the crystal is a five-coordinate linear polymer 47,380 and both tin atoms in the methanol solvate, CH2(SnPh2OMe)2-MeOH, are five coordinate, one by intramolecular coordination, and the other by solvation 48.381 Dimethyltin dimethoxide 49,382 dimethyltin diphenoxide 50,383 and isopropyltin triisopropoxide 51384 are five-coordinate oxygen-bridged dimers. All these compounds are monomers in solution. 

A good example of the simplicity and power of the chemistry to rapidly construct complex systems is provided by the Kolbe dimerization of (55) as the key step of a total synthesis of the triterpene (+)-Q -onocerin (57 Scheme 14) [33], Thus, oxidation of (+)-hydroxy keto acid (55) in methanol containing a trace of sodium methoxide and at a temperature of 50 C, followed by acylation and chromatography, provided (+)-diacetoxydione (56) in a 40% yield. 

Figure 4. Variation of relative ionic abundances with reaction time, in a high-pressure source at 5-torr CH4, for negative ions derived from deprotonation of methanol. The exponential decay of rr /z 31 yields the bimolecular rate constant for formation of the proton-bound methoxide dimer, m/z 63. In addition, at this temperature (325 K) the subsequent reaction to generate the trimer anion (m/z 95) and attainment of equilibrium can be seen.

Perfluorocyclopropene reacts readily with sodium methoxide at low temperature [22] (equation 19) Slow addition of sodium methoxide to 1,2 dichloro-3,3-di fluorocyclopropane yields initially l-chloro-2-methoxy-3,3-difluorocyclopro pane Further addition of methanol produces probably a ketal Opening of the cyclopropane ring gives an ortho ester that undergoes facile hydrolysis during the workup to form (Z)-methyl 2-fluoro-3-chloroacrylate [23] (equation 20) A per-fluorocyclobutene dimer is also very reactive and undergoes an easy SN2 displacement on treatment with ethanol [24] (equation 21)... 

Methanol is the solvent of choice for the Kolbe electrolysis. The following electrolytes with methanol as solvent have been used methanol/sodium carboxylate, methanol/sodium methoxide/carboxylic acid, methanol/water/sodium hydroxide/carboxylic acid, methanol/triethylamine/pyridine/carbox-ylic acid. An increasing amount of water often decreases the yield of dimer. 

Vanadium(V) alkoxides have been known since 1913,69 and in Table 2 we show some of the known alkoxides, the parent alcohol, and the nature of the complex in organic solvents and in aqueous solution. Alkoxides have been prepared from methanol, ethanol, isopropanol, t-butanol, silsequioxanes, cyclopentanol, cyclohexanol, norborneol, adamantanol, phenol, and other alcohols (see Table 2).70- 0 The simple complexes associate in organic solvents and dimerization in the presence of alkoxide is observed with the isopropanol complex.70 The more sterically hindred alcohols are less reactive and do not hydrolyze completely in the presence of small amounts of water.73 The first simple alkoxide to be structurally characterized was the methoxide complex (14) and the vanadium was found to be a six-coordinate dinuclear species however, the structure of this compound did not refine very well.91 This was the first report of the diamond core V—O—V—0 unit, albeit associated with two six-coordinate vanadium atoms. The diamond core V—O—V—O (11), which has since then been found to be a typical structural unit for these complexes, was distinctly asymmetric revealing a difference in the interactions between the two mononuclear parts of the molecule. The first monodentate alkoxide found to contain... 

A synthesis of dicyclopropyl ketone developed by Hart and co-workers involves in the first step a sodium methoxide-catalyzed self-condensation of y-butyrolactone (1) to the dimeric product (2). Solvent methanol is removed by distillation, eventually... 

Coextrusion of L-lactide (a cyclic dimer lactone of lactic acid) with hydroxy-terminated poly(caprolactone) in the presence of stannous octoate gave a block copolymer.74 Block copolymers can also be used as compatibilizers for the homopolymers, in addition to having interesting properties in their own right.75 Copolymers of ethylene and vinyl acetate can be treated with methanol and a little sodium methoxide to remove some of the acetate groups from the copolymer.76 The by-product methyl acetate comes out the vent of the extruder. n-Butyl alcohol can be used in the same way.77 The product copolymer is useful as a gas barrier coating on films for packaging food. 

Aminopyrimidine-5-carbonitriles can be dimerized under basic conditions to give pyrimi-do[4,5-c/]pyrimidines. Thus, the treatment of 4-aminopyrimidine-5-carbonitriles with sodium methoxide in refluxing methanol leads to 2-(4-aminopyrimid-5-yl)pyrimido[4,5-tf]pyrimidin-4-amines and 2-(4-amino-2-methylpyrimidin-5-yl)-7-methylpyrimido[4,5-t/]pyrimidine (33).111... 

This novel anodic methoxylation may proceed via the intermediacy of fluorosulfonium ion G by way of a Pummerer-type mechanism as shown in Scheme 17. In this route, the sulfide cation radical F is trapped by fluoride ion, a process which suppresses potentially complicating side reactions (such as dimerization and nucleophilic attack on an aromatic ring) of this intermediate. Because fluoride ion is a much weaker nucleophile than methoxide, it is reasonable that methoxylation predominates in methanol. Thus, fluoride ions are not incorporated into the products yet they promote the anodic methoxylation, playing the role of a mediator. 

A number of interesting reactions of the dimer (66) with nucleophiles have been described. Addition of sodium methoxide in methanol yields dimethoxy-ether (71), by replacement of the olefinic fluorine atom and of an allylic fluorine, which in turn yields keten (72) by reaction with sulphur trioxide at 30—40 Diverse... 

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