Benzylic position oxidation

In addition to oxidizing an allylic CH unit or positions a to a carbonyl, selenium dioxide can also oxidize benzylic positions to a carbonyl derivative, without oxidizing the aromatic ring. 

CrOs. Chromium oxide can also oxidize benzylic positions., as in the Etard reaction (see sec. 3.8.E). When 391 was treated with chromium trioxide in acetic acid, an 85% yield of 392 was obtained, as part of Pan s synthesis of (-)-6,7-dehydrofeiruginyl methyl ether. l... 

Oxidation (Section 11 13) Oxidation of alkylben zenes occurs at the benzylic position of the alkyl group and gives a benzoic acid derivative Oxidiz mg agents include sodium or potassium dichro mate in aqueous sulfuric acid Potassium perman ganate (KMn04) is also an effective oxidant... 

The benzylic position in tetralin can be selectively oxidized to the hydroperoxide... 

From cumene Almost all the phenol produced in the United States is prepared by this method. Oxidation of cumene takes place at the benzylic position to give a hydroperoxide. On treatment with dilute sulfuric acid, this hydroperoxide is converted to phenol and acetone. 

The benzylic position of an alkylbcnzene can be brominated by reaction with jV-bromosuccinimide, and the entire side chain can be degraded to a carboxyl group by oxidation with aqueous KMnCfy Although aromatic rings are less reactive than isolated alkene double bonds, they can be reduced to cyclohexanes by hydrogenation over a platinum or rhodium catalyst. In addition, aryl alkyl ketones are reduced to alkylbenzenes by hydrogenation over a platinum catalyst. 

SCHEME 10.2 Common pathways of QM formation in biological systems, (a) Stepwise two-electron oxidation by cytochrome P450 or a peroxidase, (b) Enzymatic oxidation of a catechol followed by spontaneous isomerization of the resulting n-quinone. (c) Enzymatic hydrolysis of a phosphate ester followed by base-catalyzed elimination of a leaving group from the benzylic position. 

Tertiary butylhydroperoxide (TBHP) is a popular oxidizing agent used with certain catalysts. Because of its size, TBHP is most effective with catalysts containing large pores however, it can also be used with small-pore catalysts. Using first-row transition metals, Cr and V, impregnated into pillared clays, TBHP converts alcohols to ketones, epoxidizes alkenes, and oxidizes allylic and benzylic positions to ketones.83-87... 

Anodic oxidation of j9-methylbenzyl-sulfonic ester, -carboxylic ester, and -nitrile in Et3N-3HF/CH3CN affords fluorides and acetamides at tbe metbyl (Me) and substituted (CH2E) benzyl position Me/CH2E = 24/76 (E = C02Et), 9/91(CN), 69/31 (SOsEt). In tbe radical bromination of these compounds, substitution at CH3 is enhanced [20],... 

Chemoselective anodic methoxylation at a distinct carbon atom in the a-position to an amino group in a polypeptide was achieved by prior introduction of a silyl group as an electroauxiliary at this carbon atom [156]. Amide oxidation in A-acetylpyrrolidines substituted with electron-rich phenyl rings led to either methoxylation a to the nitrogen atom or in the benzylic position. Mechanistic studies indicate that both the amide and the phenyl oxidation compete, but intramolecular electron transfer leads to... 

Oxidation at the benzylic position of indane -with potassium permanganate (Eq. 3.30) gives indanone in good yields and no PTC is necessary [133]. In a two-phase system consisting of an aqueous solution of KMn04 and indane in benzene an 80 % yield can be obtained under a reduced pressure of ca. 450 Torr. The authors explain this effect by the size of the cavitation bubbles, which is dictated to some extent by the over pressure. An optimal energy transformation, from acoustic to chemical, can thus take place. 

Starting from glucoside 3, the 4,6-O-benzylidene 25 could be produced by the same method, then 4,6-0-benzylidene-3-0-benzyl glucoside 11 was obtained through the same as above mentioned tin oxide benzylation method (Scheme 3). The lower yield was caused by the similar reactivity between the 2- and 3-positions of 25. 

The enzyme is the principal participant in N-demethylation reactions where the substrate is a tertiary amine. The list of substrates includes erythromycin, ethylmor-phine, lidocaine, diltiazem, tamoxifen, toremifene, verapamil, cocaine, amiodarone, alfentanil and terfenadine. Carbon atoms in the allylic and benzylic positions, such as those present in quinidine, steroids and cyclosporin A, are also particularly prone to oxidation by CYP3A4, a range of substrates is illustrated in Figure 7.10. 

A possible mechanism of oxidation of methylene groups to carbonyl groups involves autoxidation (oxidation by molecular oxygen) at the benzylic position. Autoxidation of arylalkanes is a facile reaction with low activation energies for example, 6.0 kcal/mole for 1,1-diphenylethane and 13.3 kcal/mole for toluene. ... 

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