Alcohol oxidation with chromium

I- ol, and elaborated by conjugate addition of nitrile, ketal formation, conversion with diisobutylaluminium hydride to the hydroxyaldehyde (129) and then the sequence Wittig reaction, alcohol oxidation with chromium trioxide—sulphuric acid in dimelhylformamide, ketone reduction and ketal hydrolysis to give (1)-... 

If homolytic reaction conditions (heat and nonpolar solvents) can be avoided and if the reaction is conducted in the presence of a weak base, lead tetraacetate is an efficient oxidant for the conversion of primary and secondary alcohols to aldehydes and ketones. The yield of product is in many cases better than that obtained by oxidation with chromium trioxide. The reaction in pyridine is moderately slow the intial red pyridine complex turns to a yellow solution as the reaction progresses, the color change thus serving as an indicator. The method is surprisingly mild and free of side reactions. Thus 17a-ethinyl-17jS-hydroxy steroids are not attacked and 5a-hydroxy-3-ket-ones are not dehydrated. 

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... 

ALDEHYDES FROM PRIMARY ALCOHOLS BY OXIDATION WITH CHROMIUM TRIOXIDE 1-HEPTANAL... 

Oxidations with chromium trioxide.6 Secondary alcohols can be oxidized to ketones in good yields by Cr03 in the presence of catalytic amounts of tetraalkyl-ammonium halides. Yields from oxidation of primary alcohols are moderate. 

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... 

Among compounds related to uleine that have been isolated from A. dasycarpon are X-noruleine (CCLVII-B), dasycarpidone (CCLVII-A), the corresponding alcohol, dasycarpidol, X-nordasycarpidone, and 1,1 -dihydro-l -hydroxyuleine. Dasycarpidone may be obtained from uleine by ozonolysis, or from dasycarpidol by oxidation with chromium trioxide in pyridine. l,l -Dihydro-l -hydroxyuleine has been synthesized from uleine by hydroboration (143b). Apparicine, an alkaloid of novel skeleton present in A. dasycarpon and several other species, has been shown to have the structure CCLVII-U (37). 

Metal species, including chromium,191 iron,192 cobalt,193 cerium194 and ruthenium195 compounds, have also been used to catalyse alcohol oxidation with peracetic acid. 

The same reactivity order is found with oxidation.. A number of these reactions may have radical character. Oxidation with chromium(VI) oxide (C1O3) may lead to a tertiary alcohol. 

Copper chromite, CuCr204, and mixtures of cupric oxide with chromium sesquioxide and special additives (the Adkins catalyst), dehydrogenate primary alcohols to aldehydes [354, 355] and secondary alcohols to ketones [354, 355, 356]. 

The main applications of oxidation with chromium trioxide are transformations of primary alcohols into aldehydes [184, 537, 538, 543, 570, 571, 572, 573] or, rarely, into carboxylic acids [184, 574], and of secondary alcohols into ketones [406, 536, 542, 543, 575, 576, 577, 578, 579, 580, 581, 582, 583, 584]. Jones reagent is especially successful for such oxidations. It is prepared by diluting with water a solution of 267 g of chromium trioxide in a mixture of 230 mL of concentrated sulfuric acid and 400 mL of water to 1 L to form an 8 N CrOj solution [565, 572, 579, 581, 585, 556]. Other oxidations with chromic oxide include the cleavage of carbon-carbon bonds to give carbonyl compounds or carboxylic acids [482, 566, 567, 569, 580, 587, 555], the conversion of sulfides into sulfoxides [541] and sulfones [559], and the transformation of alkyl silyl ethers into ketones or carboxylic acids [590]. 

The presence of three oxidizing species, chromium(VI), chro-mium(V), and chromium(IV) acids, accounts for differences in the oxidation products of some alcohols. Thus in the reaction of cyclobutanol with chromic acid, not only cyclobutanone but also 4-hydroxlybutanal is obtained, evidently by oxidation with chromium(V) or chromium(IV) acid via a free-radical pathway [577, 621, 654, 655, 1143] (equation 246). 

Oxidations with chromium trioxide (chromic oxide or chromic anhydride) and with chromic acid are carried out in different solvents, usually by adding solutions of chromic oxide or chromic acid to the solutions of the alcohols. When chromium trioxide dissolved in 80% acetic acid is added to a stirred solution of cis-2-phenylcyclohexanol in acetic acid at 50 °C and the mixture is allowed to stand at room temperature for 1 day, an 80% yield of 2-phenylcyclohexanone is obtained [576], Other solvents used are dimethylformamide [542], hexamethylphosphoric triamide (HMPA) [543], acetone [578, 5 i], ether [55 ], dichloromethane [555, 617], and benzene [571] (equation 249). 

A commonly used, protected carbohydrate containing a secondary hydroxy group is diiso-propylideneglucofuranose 23. Oxidation to the corresponding ketone 24 illustrates some of the most widely applied methods for oxidation of secondary alcohols (O Table 4). Again, the reactions can be divided into three main categories oxidations mediated by activated DMSO, oxidations with chromium(VI) oxides, and oxidations catalyzed by mthenium oxides. For oxidations with activated DMSO the Swern procedure is the most widely used [27]. 

In general, better results are obtained with Raney nickel catalysts, especially in large-scale reactions. The preferential formation of the thermodynamically most stable product can be used, e.g., in the synthesis of steroids from aromatic precursors such as 1324. Here hydrogenation yields the tram-fused product with a nearly equimolar mixture of the two isomeric alcohols, which can be converted into the corresponding ketone by oxidation with chromium trioxide24. 

Evidence for the structure (CXXIII) of the hemiacetal is based on the extremely hindered nature of the derived aldehyde (CXXV) and carboxylic acid (CXXVII). Thus, the aldehyde exhibited a negative Cotton effect in methanol, which remained unchanged upon the addition of hydrochloric acid, indicating great resistance toward acetal formation. Attempts to prepare carbonyl derivatives of this aldehyde were unsuccessful. The acid CXXVII was prepared by oxidation of alcohol CXXIV with chromium trioxide in acetic acid. Comparison of the apparent dissociation constant of this acid (pX cs 9.45) with that for... 

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