Beta-alkoxy reaction

For example, at the roughest level of approximation, all carbonyl carbons can be treated as identical they all have similar thermochemistry and all can undergo certain types of reactions (e.g. they all can be formed by beta-scission reactions of the corresponding alkoxy radicals). However, if one looks at the situation more carefully, the carbonyl groups in ketones, ketenes, aldehydes,... 

The alkoxy radical is usually described as a typical product of the thermal decomposition of hydroperoxides. Nevertheless, in the post-irradiation oxidation process at room temperature, it cannot originate from this reaction because all the formed products follow a kinetic similar to that of ketone formation [21]. The reaction between the alkyl macroradical and the peroxy macroradical forms peroxides (Scheme 9, Reaction 20), but we can also hypothesize Reaction 21, Scheme 9. Literature studies demonstrate that the alkoxy radical can give beta-scission (Reaction 28) forming a primary alkyl radical and CO, a product that is found during the irradiation of PE (Scheme 10, Reaction 29) [24]. The activation energy of this reaction is around 50kJ/mole. 

Guindon Y, Rancourt J. The use of Lewis acids in radical chemistry. Chelation-controUed radical reductions of substituted alpha-bromo-beta-alkoxy esters and chelation-controUed radical addition reactions. J Org Chem. 1998 63 6554-6565. 

By characterizing various zeolite catalysts under the same reaction conditions, the authors found weaker MAS NMR signals of alkoxy species for the less active zeolites HY and HZSM-5 than for the more active zeolite H-beta (250). This observation suggests that the alkoxy species observed under steady-state conditions act as reactive surface species in the MTBE synthesis from isobutylene and methanol on acidic zeolite catalysts. 

The reaction pathway is identical to that of alpha-pinene alkoxylation except no bicyclic compounds are formed. As mentioned in the literature (53, 54), alkoxylation of limonene to l-methyl-4-[alpha-alkoxy-isopropyl]-l-cyclohexene can be carried out only in the presence of acidic catalysts. After a catalyst screening using various zeolitic and non-zeolitic acid heterogeneous catalysts, we found that beta zeolite is the best candidate. 

Transition States in Acid-Cataiyzed Reactions on Zeolites. A considerable number of experimental attempts were carried out to elucidate the structure of intermediates in the acid-catalyzed reactions. This information may be used to deduce the nature of elusive transition states, which are present on the catalytic surface in concentrations far below detection limit. For example, adsorption of alcohols and unsaturated hydrocarbons on acidic zeolites gives rise to the MAS NMR signal attributed to alkoxy species (135). Transition of these surface complexes to the corresponding carbenium ions, an important step in their further transformations, was shown to have low activation energy. In the synthesis of methyl-tetrabuthyl ether on zeolite Beta, features due to secondary and tertiary carbon atoms in alkoxy species have been observed. This observation along... 

The oxidation of the sugar-containing carboxylic acid 52, in the presence of acetate, leads to the unsymmetrical bis-acetal 53 [30]. In a similar manner, 0,N-acetals can be efficiently constructed from alpha-amino-acids [24]. This process has been employed as a key step in the synthesis of some beta-lactam antibiotics [31]. The oxidative decarboxylation of alpha-alkoxy acids 58 in methanol provides a simple and efficient route to the formation of MOM ethers and obviates the use of the highly toxic MOMCl [32]. Furthermore, Mark6 et al. demonstrated that Hofer-Moest reaction of dialkoxy carboxylic acids 60 offers an easy and general route to variously functionalized orthoesters [33]. These are usually difficult to prepare by alternative methodologies and some of them can only be assembled using this electrochemical process. 

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