Alkoxy generation

For a secondary alkoxy, the products are an aldehyde and an alkyl radical. In the oxidation of a straight-chain hydrocarbon, aldehydes are likely to be major intermediates via this mechanism. They are the major precursors of acids. Because of the high reactivity of aldehydes, in most cases little aldehyde survives in the product. The alkyl radicals produced according to eq. (8) make a fresh entry into eq. (3). Tertiary alkoxys generate ketones, which oxidize much more slowly than aldehydes, but they, too, produce mostly acids [10]. 

Peroxyesters undergo single- or multiple-bond scission to generate acyloxy and alkoxy radicals, or alkyl and alkoxy radicals and carbon dioxide ... 

Monoperoxycarbonates. 00-tert-A ky O-alkylmonoperoxycarbonates (37) (eg, 00-tert-huty 0-isopropylmonoperoxycarbonate [2372-21-6]) are a class of peroxides related to peroxyesters that also generate alkoxy radicals, -OR, which again as above can undergo -scission. 

Diall l Peroxides. Some commercially available diaLkyl peroxides and their corresponding 10-h half-life temperatures in dodecane are Hsted in Table 6 (44). DiaLkyl peroxides initially cleave at the oxygen—oxygen bond to generate alkoxy radical pairs ... 

The reactions of alkyl hydroperoxides with ferrous ion (eq. 11) generate alkoxy radicals. These free-radical initiator systems are used industrially for the emulsion polymerization and copolymerization of vinyl monomers, eg, butadiene—styrene. The use of hydroperoxides in the presence of transition-metal ions to synthesize a large variety of products has been reviewed (48,51). 

Alkoxy radicals from hydroperoxides can undergo a -scission reaction (eq. 2) to yield an alkyl radical and a ketone. The higher stabiUty of the generated alkyl radical compared to that of the parent alkoxy radical provides the driving force for this reaction, and the R group involved is the one that forms the most stable alkyl radical. 

Chemical Properties. Acychc di-Z f/-alkyl peroxides efftciendy generate alkoxy free radicals by thermal or photolytic homolysis. 

RTV Silicone Chemistry. There are two basic cure chemistries used by RTV sihcones the acetoxy-based and the alkoxy-based cure systems. Acetoxy-based RTV sihcones were first commercialized in the early 1960s (422,423). The general chemical reactions of these first-generation products are shown in Figure 8. 

In general,. alkoxy- or silyloxy-isoxazolidines when treated with acid produce 2-isoxazo-lines <77AHC(2i)207, 74MIP41601). Other isoxazolidines are cleaved at the N—O bond with further degradation then following <77AHC(2i)207). The treatment of (182) with HCl generated cinnamic acid and a small amount of benzoic acid, whereas treatment of (182) with... 

The nucleophilic catalysis mechanism only operates when the alkoxy group being hydrolyzed is not much more basic than the nucleophilic catalyst. This relationship can be imderstood by considering the tetrahedral intermediate generated by attack of the potential catalyst on the ester ... 

A possible mechanism for the formation of the furanones 6 and 7 is illustrated in Scheme 2. The initial alkoxy radical generated from the alcohol 5 and lead tetraacetate (LTA) undergoes /3-scission to produce the acyl radical intermediate 9. Subsequent cyclization to 10 proceeds through attack of the radical at the carbonyl oxygen. The resulting Pb(IV) intermediate 11 finally collapses via the reductive... 

In addition to alkyl-substituted derivatives, soluble PPPs 6 are also known today containing alkoxy groups as well as ionic side groups (carboxy and sulfonic acid functions) [18]. Schliiter et al. recently described the generation of soluble PPPs decorated with densely packed stcrically demanding dendrons on the formation of cylindrically shaped dendrimers, so-called cylinder dendrimers ] 19]. 

The a-alkoxy iron-acyl complex 5 may be deprotonated to generate the lithium enolate 6, which undergoes a highly diastereoselective aldol reaction with acetone to generate the adduct 7 as the major product. Deprotonation of acetone by 6 is believed to be a competing reaction 30% of the starting complex 5 is found in the product mixture48 40. 

Treatment of a-alkoxy-substituted iron acyl complexes 20 with bromine in the presence of an alcohol produces free acetals 22 with loss of stereochemistry at the center derived from the a-carbon of the starting complexl2,49. Electron donation from the alkoxy group allows formation of the oxonium intermediate 21, which is captured by the alcohol to generate the product acetal. 

For diastereoselective addition of pcrfluoroalkyl lithium generated in situ to imines and %-alkoxy imines in the presence of BF, OEt2. see refs 13 and 14. 

Oxygen-centered radicals are arguably the most common of initiator-derived species generated during initiation of polymerization and many studies have dealt with these species. The class includes alkoxy, hydroxy and aeyloxy radicals and tire sulfate radical anion (formed as primary radicals by homolysis of peroxides or hyponitrites) and alkylperoxy radicals (produced by the interaction of carbon-centered radicals with molecular oxygen or by the induced decomposition of hydroperoxides). 

For a related study of intramolecular nucleophilic addition by an alkoxy group without generation of any new stereogenic center, see Reference 94. 

Non-heteroatom-stabilised Fischer carbene complexes also react with alkenes to give mixtures of olefin metathesis products and cyclopropane derivatives which are frequently the minor reaction products [19]. Furthermore, non-heteroatom-stabilised vinylcarbene complexes, generated in situ by reaction of an alkoxy- or aminocarbene complex with an alkyne, are able to react with different types of alkenes in an intramolecular or intermolecular process to produce bicyclic compounds containing a cyclopropane ring [20]. 

The superior donor properties of amino groups over alkoxy substituents causes a higher electron density at the metal centre resulting in an increased M-CO bond strength in aminocarbene complexes. Therefore, the primary decarbo-nylation step requires harsher conditions moreover, the CO insertion generating the ketene intermediate cannot compete successfully with a direct electro-cyclisation of the alkyne insertion product, as shown in Scheme 9 for the formation of indenes. Due to that experience amino(aryl)carbene complexes are prone to undergo cyclopentannulation. If, however, the donor capacity of the aminocarbene ligand is reduced by N-acylation, benzannulation becomes feasible [22]. 

There has been a plethora of recent hterature regarding the synthetic manipulations of the 2(lH)-pyrazinone skeleton. Even though the addition-elimination reactions at the C-3 position to decorate the pyrazinone scaffold are well documented [24], the versatihty of such approaches can be found somewhat limited. Selective attack of nucleophiles on the chloroimine group of the pyrazinone system can generate 3-alkoxy- and 3-amino-pyrazinones (Scheme 9) [27,28]. The 3-CN group was introduced via a Rosemund-von Braun reaction with copper(I)cyanide under harsh conditions (heating in NMP at 150 °C) [27] (Scheme 9). 

Hoomaert has studied Diels-Alder reactions of pyridine oquinodimethane analogs generated from functionalized o-bis(chloromethyl)pyridines <96T(52)11889>. The photochemical cycloaddition of 2-alkoxy-3-cyano-4,6-dimethylpyridine with methacrylonitrile gives a bicyclic azetine, 6-alkoxy-3,5-dicyano-2,5,8-trimethyl-7-azabicyclo[4.2.0]octa-2,7-diene, in moderate yield <96CC1349>. Regiospecific hydroxylation of 3-(methylaminomethyl)pyridine to 5-(methylaminomethyl)-2-(17/)-pyridone by Arthrobacter ureafaciens has been reported <96MI173>. 

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