Cyclobutanol, oxidation

A material with nitrogen-coordinated Ru was obtained from a silica-linked 2-(phenylazo)pyridine ligand. Results for cyclobutanol oxidation with 02 and the sacrificial oxidant isobutyraldehyde indicate that one- and two-electron oxidations occur simultaneously. The stability of the catalyst is not always guaranteed, probably because acids may be formed in oxidations of alcohols (284). Leaching problems are also encountered with a polymer-bound Ru Schiff base complex, used in oxidation of benzyl alcohol (285). 

Cyclobutanols oxidize with ring cleavage to 4-hydroxy ketones, 4-hydroxy acids, or 1,4-diones under the influence of chromium(Vl) reagents (Scheme 11). The first formed product is a 4-hydroxycarbonyl compound (31) which exists as the five-membered ring hemiacetal (32). This form will persist in the absence of excess reagent under nonforcing conditions otherwise further oxidation takes place to give a... 

Oxidation of cyclobutanol by a Cr(VI)-V(IV) couple appears to involve attack of Cr(IV) upon the substrate to yield a free radical, (Section 2.5). This implies the following possible variation in the Westheimer scheme for a secondary alcohol ... 

Preliminary results have been reported of oxidation of cyclobutanol by the Cr(VI)-V(IV) couple to 4-hydroxybutyraldehyde. This proceeds at the same rate as the oxidation of V(IV) by Cr(VI) and cannot involve attack of Cr(V) upon the alcohol, for this oxidation state is formed in a rapid pre-equilibrium, but rather attack by Cr(IV), viz. 

The alkoxide generated by KH in THF was believed to be effective in accelerating the vinylcyclobutane ring expansion in the synthesis of 6-membered ring compounds 142). As an example, the cyclobutanol (416) reacted with KH and rearranged to (417), which upon subsequent oxidation, provided (418) 142) in 64.5% yield. The a,P-unsaturated ketone (418) was converted to (—)- 3-selinene (419)142). Similarly, furancyclohexanol (421) could be obtained from the cyclobutanol (420) 142). 

The cyclobutanols (458) underwent oxidative cleavage with chromic acid to provide diketones (459) (Table 19)157). 

The mechanism of the oxidation of tertiary cyclobutanols with Jones reagent is believed to involve the intermediate lactols (Eq. (18)) and the cleavage of the lactol to ketol and its subsequent oxidation to diketone when R1 = H157). 

Various oxidation conditions which could promote the ring cleavage of cyclobutanols have been briefly reviewed 158). This work was extended to the cyclo-... 

The absence of any acyclic products from the reaction of cyclobutanol with RuO suggests that clean two-electron steps are involved [276]. Kinetic data for the oxidation of 2-propanol to acetone by RuOyaq. HCIO indicated that at moderate acidities the rate-determining step involves hydride abstraction, while at very high acid concentrations carbonium ions may be formed [277]. 

All of the usual chromium-based oxidation reagents that have been used for the oxidation of cyclobutanols to cyclobutanones, for example, chromium(VI) oxide (Jones reagent),302 pyri-dinium chlorochromate,304 pyridinium dichromate,307 and chromium(YI) oxide/pyridine (Collins),303 are reported to do so without any serious problems. Alternatively, tetrapropylam-monium perruthenate in the presence of A-methylmorpholine A -oxide. oxalyl chloride in the presence of triethylamine in dimethyl sulfoxide (Swern),158,309,310 or phenyl dichlorophos-phate in the presence of triethylamine and dimethyl sulfoxide in dichloromethane (Pfitzner-Moffatt),308 can be used. The Pfitzner-Moffatt oxidation procedure is found to be more convenient than the Swern oxidation procedure, especially with respect to the strict temperature control that is necessary to achieve good yields in the latter, e.g. oxidation of 1 to give 2.308... 

Examples of the oxidation of cyclobutanols to cyclobutanones are given in Table 14. 

The photochemistry of isomesityl oxide is rather interesting in that cyclobutanol formation and type I cleavage proceed with a fair quantum yield.361 The efficiency of the process may indicate that energy transfer to the double bond is not favored.361 However, it is likely that most of the photoreaction proceeds from an excited singlet. 

Posner et al. found that commercial aluminium oxide is able to promote the oxidation of alcohols employing chloral as hydride acceptor.30 The reaction operates at room temperature in inert solvents like CCI4 and surprisingly no base-induced condensations are reported. Basically, the same experimental conditions were later applied for the oxidation of cyclobutanol,31 a compound with a great propensity to fragmentation under the action of other oxidants. 

A modified Oppenauer oxidation, using activated neutral chromatographic alumina and chloral in CCI4 at room temperature, allows the oxidation of cyclobutanol in ... 

The oxidation of cyclopropanecarbinol under Oppenauer conditions using ciiinamaldehyde as oxidant leads to the desired aldehyde contaminated with cyclobutanol, which probably arises from a ring expansion promoted by a complexation of the alcohol with the aluminium atom operating as a Lewis acid. 

The photochemical addition of cyclic 1,3-diones such as dimedone, 1,3-cylohexandione 62, or their respective silyl enol ethers leads to the formation of two fused furanylfullerenes, (1) achiral 63 and (2) chiral 64 [244], The latter having an unusual bis-[6,5] closed structure. In the initial step of this reaction, [2 + 2] photocycloaddition across a [6,6] bond to form cyclobutanols or the corresponding TMS ethers is involved (Scheme 26). Oxidation with 02 yields in the formation of the radical 65a. Cleavage to 66a followed by cyclization gives furanyl radical 67a. H abstraction by 102 or a peroxy radical finally leads to product 63. In competition, formation of fullerene triplets by absorption of a... 

Another type of carbopalladation is observed in the oxidation of the 2,2-disubstituted alkene attached to the cyclobutanol 104. The shift of the carbon-carbon bond as shown by 105 and ring expansion generate 106. Intramolecular alkene insertion gives the bicyclo[4.3.0]nonane system 107. Finally, 108 is obtained [78],... 

Very similar product mixtures are obtained from electrochemical decarboxylations or deoxidations 201 and deaminations 202 of the corresponding alcohols or amines. Anodic oxidation of cyclobutanecarboxylic acid affords in 30% yield a mixture of cyclopropylcarbinol, cyclobutanol and allylcarbinol identical in composition with that obtained from deamination of cyclobutylamine 203 Electrolysis of exo- or encfo-norbornane-2-carboxylic acid gave exo-norbornyl-2-... 

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