Alcohols, reaction with manganese dioxide

It should be noted, however, that the lack of electron density in the 7t-system may be bypassed by creating local (T-electron density by lithiation and reaction with suitable electrophiles. Quenching of lithiated alkoxy-l,2,3-triazines with aromatic aldehydes generates (a-hydroxybenzyl)-l,2,3-triazines, products of an electrophilic attack on carbon. Dehydrogenation of their alcohol function with manganese dioxide affords formal Friedel-Crafts acylation products <1998MI119>. Lithiation has been discussed from a theoretical point of view in Section 9.01.2.13, and practical implications are presented in Section 9.01.5.5. 

In comparison with manganese dioxide, the DDQ reagent has several advantages for the oxidation of allylic alcohols. The quinone method is more reproducible only one equivalent of oxidant need be added and generally fewer side reactions are observed. On the other hand, the workup of DDQ reactions often requires chromatography and in the simpler cases lower isolated yields may be realized. 

The alcohol 172 obtained by reaction of 86 with ethynyl magnesium bromide on oxidation with manganese dioxide gave the ketone 17361 Glaser coupling of the ketone 173 gave an equimolar mixture of the two acyclic diketones 170 and 174. 

In the second, the use of diazopropane is avoided the alcohol (250) is converted to the pyrazole (251) by a two step sequence of reaction with hydrazine in acetic acid and then oxidation with manganese dioxide. Photolysis then leads cleanly to the cyclopropene, without any interference by cyclisation of an intermediate carbene to the alcohol group the product is hydrogenated directly, the conversion of (251) to (252) occurring in 94% yield. Elimination of the elements of water leads to m-chrysanthemic acid in good overall yield 175) ... 

A different type of ester formation takes place when a,(3-unsaturated alcohols are oxidized with manganese dioxide and subsequently treated with sodium cyanide, acetic acid, manganese dioxide, and methanol. The final result is shown by the sequence of reactions in equation 238 [382]. 

This reaction was first reported by Corey and co-workers in 1968. It is an efficient synthesis of o ,j8-unsaturated esters by treatment of o, j0-unsaturated aldehydes (or allyl aicohois) with manganese dioxide and potassium cyanide in a proper alcohol. This reaction is thus known as the Corey-Gilman-Ganem oxidation in general or simply the Corey-Ganem oxidatin. ... 

Enhancing the utility of the allq lation-rearrangenient sequence in synthesis, the Evans group addressed the problems of a-versus-y alkylation as well as low anion reactivity by employing heterocyclic sulfides as the alleviation substrates tScheme IR.IfiE For instance, allylic imidazolyl sulfide 56 could be allqvlated efficiently, reaction at the a-position being favored by a chelated but reactive allyl lithium intermediate. Oxidation of 57 to the allylic sulfoxide and treatment with a secondary amine thiophile provided allylic alcohol 58 in high yield and with excellent stereoselectivity at the trisubstituted alkene. Allylic oxidation with manganese dioxide completed a synthesis of the sesquiterpene nuciferal (59). ... 

Nickel peroxide is a solid, insoluble oxidant prepared by reaction of nickel (II) salts with hypochlorite or ozone in aqueous alkaline solution. This reagent when used in nonpolar medium is similar to, but more reactive than, activated manganese dioxide in selectively oxidizing allylic or acetylenic alcohols. It also reacts rapidly with amines, phenols, hydrazones and sulfides so that selective oxidation of allylic alcohols in the presence of these functionalities may not be possible. In basic media the oxidizing power of nickel peroxide is increased and saturated primary alcohols can be oxidized directly to carboxylic acids. In the presence of ammonia at —20°, primary allylic alcohols give amides while at elevated temperatures nitriles are formed. At elevated temperatures efficient cleavage of a-glycols, a-ketols... 

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