Intermediates, reaction methoxy intermediate

Transient carbene (9) is expected to be a reaction intermediate in the transformation of butadiyne-linked triazene (8) to alkyne-linked bis-2//-indazolcs (10).18 Experimental data and DFT calculations support carbene (9) as an intermediate in this stepwise, non-synchronous coarctate reaction. Methoxy(methylthio)carbene (12) has been observed by UV photoelectron spectroscopy after gas-phase decomposition of oxadiazoline (11).19 The oxadiazoline (13) allows the generation of the acetoxy(methoxy)carbene (14) 20 -pjjg reaC jvj y 0f (he latter with isocyanates has been explored. Such reactions generally yield methyl (acetylamino)oxoacetates (15). DFT calculations permitted interpretation of the experimental data. 

Cyclic olefins preferably undergo twofold carbonylation, even without the presence of buffer compounds such as sodium acetate. With methanol serving as the solvent and under comparable reaction conditions to those mentioned above, cycloalkenes give product mixtures consisting of methyl rrans-2-methoxy-cycloalkanecarboxylates, dimethyl cw-cycloalkane-l,2-dicarboxylates and dimethyl cw-cycloalkane-1,3-dicarboxylates (eq. (3) and Table 1). The formation of 1,3-diesters may be explained by an intermediate reaction sequence which involves an oxidative elimination and a subsequent readdition of the Pd species, thus giving rise to an isomerization [9]. 

Metallation of l-methoxy-2-butyne with n-butyllithium at -78 C, followed by the addition of one equivalent of zinc chloride, generates the very reactive and unisolable organozinc intermediate. Reaction of this zinc reagent with cyclohexenone affords the alkynic alcohol in 95% yield as a 65 35 mixture of diasteieomers. Subsequent reduction of the triple bond provides either the trans alkene or the cis alkene, depending on the reaction conditions. A modified oxy-Cope rearrangement thus provides the dia-steieomeric ketones, which have been used for the synthesis of juvabione (Scheme 29). ... 

The kinetics of methanol oxidation over metal oxide catalysts were elegantly derived by Holstein and Machiels [16], The kinetic analysis demonstrated that the dissociative adsorption of water must be included to obtain an accurate kinetic model. The reaction mechanism can be represented by three kinetic steps equilibrated dissociative adsorption of methanol to a surface methoxy and surface hydroxyl (represented by K,), equilibrated dissociative adsorption of water to two surface hydroxyls (represented by K ), and the irreversible hydrogen abstraction of the surface methoxy intermediate to the formaldehyde product and a surface hydroxyl (the rate determining step, represented by kj). For the case of a fully oxidized surface, the following kinetic expression was derived ... 

Methanol-like or methoxy intermediates undergo a CO insertion and are thereby transformed into C2 intermediates. (4) Two molecules of CO on the same site combine into C2 species. (5) Methanol undergoes a consecutive condensation reaction in the adsorbed state with another methanol molecule, or with another alcohol, to produce higher alcohols. 

In the case study for methanol dehydrogenation, ab initio electrochemical calculations identified the presence of a dual reaction pathway that proceeds through the formation of the hydroxymethyl intermediate as the dominant path to form CO and the formation of the methoxy intermediate as the path to form formaldehye. Differences in the electronic structure of the adsorbed methoxy and hydroxymethyl ultimately control the onset of the dual path at potentials lower than about 0.5 V. While these results are encouraging, theory has only just begun to tackle the complexity of the electrocatalytic systems. 

The anions derived from phenols are bidentate nucleophiles and can react through of the O- or the C-atoms. For example, the 2-naphthoxide ions 65 react with ArX to give substitution only at C-1 of the naphthalene ring [61]. In this reaction, the intermediated Ar radical couples in C-1 of 65 to yield the radical anion 66, which by ET gives the product 67 that after tautomerization yields the more stable products 68 (Eq. 10.25). The rates of reactions of 2- and 4-anisyl and 2-methoxy-l-naphthyl radicals with 65 were determined (10 -10 M s" ) using an indirect method, a competition of the coupling reaction with the H-atom abstraction from the DMSO [62] ... 

The heterocyclic intermediates for bensulfuron methyl and chlorimuron methyl are prepared from 2-amino-4,6-dichloropyrimidine (XVII) (Equation 14). This intermediate was prepared by the reaction of dimethyl malonate and guani ne carbonate to yield 2-amino-4,6-dihydroxypyrimidine which is converted to the dichloro compound by phosporus oxychloride. Treatment of the dichloro intermediate with sodium methoxide and methanol gave the dimethoxy intermediate (XVin) for bensulfuron methyl, whereas with potassium carbonate and methanol the product is the 4-chloro-6-methoxy intermediate (XIX) for chlorimuron methyl. 

Surface methoxy groups are the intermediate reaction species in the production of partially oxygenated reaction products (formaldehyde, methyl formate, methylal, etc.) during methanol selective oxidation on catalysts containing transition metal oxides (oxides of vanadium, molybdenum, chromium, etc.). Therefore, the knowledge of the amount of surface methoxy species formed during methanol chemisorption is the key for the determination of the number of surface active sites... 

Figure 6 (a) Reaction eneigy diagram for DME formation via a surface methoxy intermediate involving one methanol molecule at each step... 

In the proposal for the methane-formaldehyde mechanism, methane and formaldehyde are formed from the surface methoxy intermediates and react to form ethanol [83-86]. Tajima et al. [83] used theoretical calculations to indicate that CHyHCHO are also potential reaction intermediates, van Santen with Blaszkowski [86] have theoretically found a transition state for hydride transfer between methanol and surface methoxy to form methane and potentially formaldehyde. Because methane is very slow to react, almost all conventional experimental and theoretical studies have supposed methane to be independent of the first C-C bond... 

An active catalytic species in the dimerization reaction is Pd(0) complex, which forms the bis-7r-allylpalladium complex 3, The formation of 1,3,7-octa-triene (7) is understood by the elimination of/5-hydrogen from the intermediate complex 1 to give 4 and its reductive elimination. In telomer formation, a nucleophile reacts with butadiene to form the dimeric telomers in which the nucleophile is introduced mainly at the terminal position to form the 1-substituted 2,7-octadiene 5. As a minor product, the isomeric 3-substituted 1,7-octadiene 6 is formed[13,14]. The dimerization carried out in MeOD produces l-methoxy-6-deuterio-2,7-octadiene (10) as a main product 15]. This result suggests that the telomers are formed by the 1,6- and 3,6-additions of MeO and D to the intermediate complexes I and 2. 

Some Hammett values for reactions in thiazole and in nucleophile are reported in Table V-3. The observed p values for normal substitution processes (methoxy and thiophenoxysubstitution) are high and positive, indicating that the substituent plays an important role in modifying the stability of the intermediate anion. 

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