Chromium trioxide benzylic oxidation

Again, as with pyridopyrimidines, the main reaction is oxidation of di- or poly-hydro derivatives to fully aromatic structures, often merely by air or oxygen. In some cases the reagent of choice is mercury(II) oxide, whilst other reagents used include sulfur, bromine, chloranil, chromium trioxide-acetic acid, hydrogen peroxide, and potassium ferricyanide, which also caused oxidative removal of a benzyl group in the transformation (306) (307)... 

ALDEHYDES FROM PRIMARY ALCOHOLS BY OXIDATION WITH CHROMIUM TRIOXIDE 1-HEPTANAL, 52, 5 ALDEHYDES FROM sym-TRITHIANE n-PENTADECANAL, 51, 39 Aldehydes, acetylenic, 54, 45 Aldehydes, aromatic, 54, 45 Aldehydes, benzyl, 54, 45 Aldehydes, olefinic, 54, 45... 

Synonym Gamma-Chloropropylene Oxide 3-Chloro-1,2-Propylene Oxide Chlorosulfonic Acid Chlorothene Chiorotoluene, Alpha Alpha-Chlorotoluene Omega-Chlorotoluene Chlorotrifluoroethylene Chlorotrimethylsilane Chlorsulfonic Acid Clilorylen Clip Chromic Acid Chromic Anhydride Chromic Oxide Chromium (VI) Dioxychloride Chromium Oxychloride Chromium Trioxide Chromyl Chloride Cianurina Citric Acid Citric Acid, Diammonium Salt Clarified Oil Clorox Cc Ral Coal Tar Oil Cobalt Acetate Cobalt Acetate Tetrahydrate Cobalt (II) Acetate Cobalt Chloride Cobalt (II) Chloride Cobaltous Acetate Cobaltous Chloride Cobaltous Chloride Dihydrate Cobaltous Chloride Hexahydrate Cobaltous Nitrate Cobaltous Nitrate Hexahydrate Cobaltous Sulfate Heptahydrate Cobalt Nitrate Cobalt (II) Nitrate Cobalt Sulfate Compound Name Epichlorohydrin Epichlorohydrin Chlorosulfonic Acid Trichloroethane Benzyl Chloride Benzyl Chloride Benzyl Chloride Trifluorochloroethylene Trimethylchlorosilane Chlorosulfonic Acid Trichloroethylene Cumene Hydroperoxide Chromic Anhydride Chromic Anhydride Chromic Anhydride Chromyl Chloride Chromyl Chloride Chromic Anhydride Chromyl Chloride Mercuric Cyanide Citric Acid Ammonium Citrate Oil Clarified Sodium Hypochlorite Coumaphos Oil Coal Tar Cobalt Acetate Cobalt Acetate Cobalt Acetate Cobalt Chloride Cobalt Chloride Cobalt Acetate Cobalt Chloride Cobalt Chloride Cobalt Chloride Cobalt Nitrate Cobalt Nitrate Cobalt Sulfate Cobalt Nitrate Cobalt Nitrate Cobalt Sulfate... 

Methoxy-2-tetralone was methylated by the Stork method to yield 337. The latter was treated with sodium hydride and benzyl chloromethyl ether to furnish compound 338 in 60% yield. Ketalization of 338 afforded the ketal 339 which was hydrogenated with palladium on calcium carbonate to give the alcohol 340 in a yield of 92%. The alcohol 340 was oxidized with chromium trioxide in pyridine to afford the aldehyde 341 in quantitative... 

Benzaldehyde is prepared by the hydrolysis of (dichloromethyl)benzene (benzal chloride) in either aqueous acid or aqueous alkali and by the oxidation of toluene with chromium trioxide in acetic anhydride (Scheme 6.3). In the latter synthesis, as the benzaldehyde is formed, it is converted into its diacetate by the acetic anhydride, so preventing further oxidation subsequent hydrolysis generates the aldehyde group. The benzaldehyde has thus been protected from oxidation. Benzyl alcohol can... 

While removal of an AT-alkyl substituent is not always a feasible process benzyl groups can be removed by reduction with sodamide or by catalytic hydrogenolysis. If such reductive methods fail, an oxidation with chromium trioxide in acid may be successful. Other groups are not so readily displaced, but a procedure involving transalkylation with benzyl chloride followed by debenzylation can be employed to convert 1-methylimidazole into imidazole (Scheme 137). The reaction is capable of extension and operates because the quaternary salt is in equilibrium with both 1-alkylimidazoles and the alkyl halides. Under conditions in which the more volatile alkyl halide can escape from the system the 1-benzylimidazole builds up. 

Dimethylaminopyridinium chlorochromate, 4-(CH3)2NCsH4NH CrOsCI, is a yellow-orange solid prepared by the addition of 1 mol of 4-liimethylaminopyridine to a solution of 1 mol of chromium trioxide in dilute hydrochloric acid. The reagent is light sensitive [530]. For the oxidation of allylic and benzylic alcohols to aldehydes in dichloromethane at room temperatures, 4-6 mol of 4-dimethylaminopyridinium chlorochromate is used. Saturated alcohols are not oxidized [5Jd]. 

Secondary benzylic chlorides and bromides give aromatic ketones on oxidation with chromium trioxide [5<5f>] or with tetrabutylammonium hypochlorite [690] (equations 198 and 199). 

The oxidation of diols having alcoholic groups of the same nature, for example, both alcoholic groups are primary, secondary, allylic, or benzylic, is usually carried out at both groups to yield dialdehydes [832] or diketones [552], Such reactions are achieved by chromium trioxide [582], barium manganate [832], dimethyl sulfoxide activated with acetic anhydride [1013], and others (equations 284 and 285). 

Tribromo-m-cresol is oxidized by chromium trioxide in 70% acetic acid at 70-75 °C within 10 min to dibromo-m-toluquinone (3,5-dibromo-2-methyl-p-benzophenone) in 77% yield [559]. 2-BVomo-4-hy-droxy-5-methoxybenzyl alcohol treated with Fremy salt at pH 6 at room temperature for 1 h gives an 84% yield of 2-bromo-5-methoxy -benzo-quinone [487]. 4-Benzyl-2,6-dibromophenol, on oxidation with bromine in a sealed tube, yields 2,6-dibromophenylchinomethide [732] (equation 312). The oxidation of 2,5-di-tert-butyl-4-methoxyphenol with mercuric oxide or... 

Chromium trioxide (CrOs) immobilized on premoistened alumina affords efficient oxidation of benzyl alcohols to carbonyl compounds by simple mixing (Scheme 7). Remarkably, neither the over-oxidation to carboxylic acids nor the formation of tar, a typical occurrence in many CrOs oxidations, is observed. ... 

New reactions of isoquinoline derivatives include the following 3,4-di-hydroisoquinoline N-oxide with 2-acetylcycloalkane-l,3-diones, Reissert compounds with stilbene and tolan derivatives, isoquinoline with pyrrole derivatives and with 2-methylfuran " (both in the presence of benzyl chloride), and the chromium trioxide oxidation of the benzo[a]quinolizidine (49) to give (50). Compound (49) was prepared by the condensation of 3,4-dihydroiso-quinoline with the 5-lactone (51). Further examples of a classical benzo[a]-... 

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... 

Cobalt chloride in diglyme is a useful catalyst for benzylic [22a] and allylic [22b] oxidation under mild conditions. The addition of sodium azide to oxidations catalyzed by transition metal acetylacetonates, heteropolyacids, phtha-locyanines, bis-(pyridylimino)isoindolines, porphyrins and Schiff bases significantly enhances the rates of the low-temperature catalytic oxidation of alkanes [22c]. Ethylbenzene is slowly oxidized by air in MeCN in the presence of catalytic amount of chromium trioxide [23]. Complexes of Fe(III) and Co(II)... 

Use of chromium(VI) reagents for oxidative transformation is compromised by their inherent toxicity, involved preparation of the various complex forms (with pyridine or acetic acid), and cumbersome work-up procedures. Chromium trioxide (CrOa) immobilized on premoistened alumina enables efficient oxidation of benzyl alcohols to carbonyl compounds by simple mixing with different substrates... 

Oxidation with acid solutions of chromic acid is normally unsuitable for alcohols that contain acid-sensitive groups or other easily oxidizable groups, such as allylic or benzylic C—H bonds elsewhere in the molecule. However, the end-point of the oxidation can in many cases by observed by the persistence of the red colour of the chromic acid. Therefore the reaction can be monitored by dropwise addition of a solution of chromium trioxide in aqueous sulfuric acid to a cooled (0-20 °C) solution of the alcohol in acetone, thereby adding only the stoichiometric amount... 

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