Cyclohexanol, 2-alkoxy

Oxidation of tertiary alcohols by lead tetraacetate gives alkyl radicals by /3-scission of the initially formed alkoxy radicals. The reaction has been used to alkylate protonated heteroaromatic bases using 1-methyl-cyclohexanol. (Scheme 4). 

A review by Schuchardt et al. thoroughly analyses the various catalytic systems reported in the literature up to 2000, both homogeneous and heterogeneous ones, and those that use oxidants other than oxygen [e.g., HP or t-butyl hydroperoxide (f-BuOOH)[ [2c[. The mechanism involves the formation of cyclohexanol via the cyclohexyl radical and cyclohexyl hydroperoxide. According to the Haber-Weiss mechanism, cyclohexyl hydroperoxide decomposes into alkoxy and alkyloxy radicals (Section 7.2.1). Cyclohexanol is finally oxidized to cyclohexanone. A similar mechanism may occur at the a-C, affording 1,2-cyclohexanedione, which is finally cleaved to AA. Oxidation of the intermediately formed cyclohexanone to AA then occurs through a mechanism similar to that illustrated in Scheme 7.5. 

The oxo-oxidation products from cyclohexane with tBuOOH arc cyclohcxyl peroxide and its decomposition products, cyclohexanol and cyclohexanone. The relative ratio of the hydroperoxide decomposition products depends on its decomposition mechanism (see scheme). After a homolytic 0-0 bond cleavage in the peroxide, the formed alkoxy radical can undergo disproportionation, yielding equal amounts of ol/onc. A high ketone yield results from the peroxide dehydration with a Lewis acid, such as l e(OII) formed by H2O2 decomposition on free Fe. 

Chemical reactions with the radicals formed during the primary processes are also found to be responsible for synergistic effects, e.g. in a combination of 1 and 1 -benzoyl cyclohexanol 3. in aerated medium. A possible explanation [23] is based on the decomposition by 1 of the hydroperoxides arising from the oxidation of the radicals generated through cleavage of 3- The weak reactivity of these peroxy radicals compared to alkoxy and hydroxy radicals (Scheme 2) and the concommittant reduction of air inhibition due to the consumption of dissolved oxygen by excited benzophenone can be also invoked to account for the experimental observations. 

Summary The interaction of organoacetoxysilanes with menthol, eugenol, vanillin, citronellol, phenol, cyclohexanol and hexanol was investigated. Products of full and partial esterification were obtained. The hydrolysis of alkoxy(aroxy)silanes and acetoxyalkoxy(aroxy)silanes in a solution of methyl ethyl ketone or THF and on a cellulose surface was investigated. Rates of acetoxyalkoxy(aroxy)silane hydrolysis on the cellulose surface were by 1-2 orders lower than in a solution, but the dependence on the nature of the substituents remained. 

Mansuy et al. employed alkyl peroxides and iodosylbenzene as oxygen donors and examined the oxidation products of cyclohexane in the presence of a series of M(TPP) complexes (M=Fe, Mn, Co, Rh, and Cr) [284]. As listed in Table 10, cyclohexanol and cyclohexanone are the major products however, the ratio of the alcohol and ketone was dependent on the oxidant employed. For the oxidation by peroxides, involvement of alkoxy radical (RO ) due to the homolytic 0-0 bond cleavage of R-OO-M was proposed. In order to trap possibly formed radical intermediates. He and Bruice examined the oxidation of cw-stilbene and (Z)-l,2-bis(fran5-2,tran5-3-diphenylcyclopropyl)ethane by iron porphyrin/f-BuOOH system [285]. In separate experiments, AIBN was used as a radical chain initiator for the oxidation of the alkenes by t-BuOOH. According to the product distribution, they concluded the products to be derived from initial combination of t-BuOO, rather than 0=Fe (por)", with olefin. 

Further work on the preparation of cryt/iro-2-alkyl-3-hydroxy-esters (140) by various condensations between propionic acid derivatives and aldehydes has been reported " the use of zirconium enolates seems to be particularly efficacious. Rules for predicting the stereochemical outcome of condensations between lithium enolates of esters and ketones and a-alkoxy-aldehydes have also been delineated. Pure erythro-isomer (140) can also be obtained in some cases by reduction of the corresponding jS-keto-ester with zinc borohydride. In related work it has been found that sodium borohydride in isopropanol reduces t-butyl a-alkoxy-j8-keto-esters to the corresponding -hydroxy compounds with erythro-threo ratios of between 2 1 and 20 1 in favour of the eryt/iro-isomer. In an extension of his previous work, Frdter has reported that dianions derived from cyclohexanol (141) can be alkylated with 95% stereoselectivity, to give (142). When the starting alcohol (141) is optically pure, a sequence of alkylation and oxidation leads to 2-ethoxycarbonylcyclohexanones with 76% enantiomeric enrichments. 

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