Oxidations of alcohols with manganese dioxide

Another reagent that has applicability for oxidation of alcohols to ketones is ruthenium tetroxide. For example, the oxidation of 1 to 2 was successfully achieved with this reagent after a number of other methods failed. 

This is a potent oxidant, however, and it readily attacks carbon-carbon double bonds.  

A very useful group of procedures for oxidation of alcohols to ketones have been developed that involve dimethyl sulfoxide (DMSO) and any one of a number of electrophilic molecules, particularly dicyclohexylcarbodiimide, acetic anhydride, trifluoroacetic anhydride, oxalyl chloride, and sulfur trioxide. The initial work involved the DMSO-dicyclohexylcarbodiimide system.The utility of the method has been greatest in the oxidation of molecules that are highly sensitive to more powerful oxidants and therefore cannot tolerate alternative methods. The mechanism of the oxidation involves formation of intermediate A by nucleophilic attack of DMSO on the carbodiimide, followed by reaction of this species with the alcohol. A major part of the driving force for the reaction is derived from the conversion of the carbodiimide to a urea, with formation of an amide carbonyl.  

SECTION 10.1. OXIDATION OF ALCOHOLS TO ALDEHYDES, KETONES, OR CARBOXYLIC ACIDS 

Oxidation of alcohols under extremely mild conditions can be achieved by a procedure that is mechanistically related to the DMSO method. Dimethyl sulfide is converted to a sulfonium derivative by reaction with iV-chlorosuccinimide. This sulfur species reacts readily with alcohols, generating the same kind of alkoxysul-fonium salt that is involved in the DMSO procedures. In the presence of mild base, elimination of dimethyl sulfide completes the oxidation.Similarly, reaction of 

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Scheme 12.2. Oxidation of Alcohols with Manganese Dioxide...

Figure 19.1 Synthetic scheme for example pheromone components. Abbreviations al and a2 = Wittig-Homer condensations with triethyl 2-phosphonopropionate and triethyl 2-phosphonobutyrate, respectively b = reduction of ester with lithium aluminum hydride c = partial oxidation of alcohol with manganese dioxide to aldehyde dl and d2 = Wittig condensations with ethyltriphenylphosphonium bromide and propyltriphenylphosphonium bromide, respectively e = condensation with dimethylhydrazone phosphonate reagent f = hydrolysis under acidic conditions. Compound numbers are as in Table 19.1.

Oxidation of tazettinol with manganese dioxide afforded 2-(4-hy-droxyphenyl)-4,5-methylenedioxybenzyl alcohol. Presumably the primary oxidation product (CLVI) underwent jS-elimination to give CLVII,... 

Pratt, E. E, and McGovern, T. P, Oxidation by solids. 1. Oxidation of selected alcohols by manganese dioxide, J. Org. Chem., 26, 2973, 1961 Pratt, E. E, and Van de Castle, J. E, Oxidation by solids. 11. The preparation of eithertetraarylethanes or diarylketones by oxidation of diarylmethanes with manganese dioxide,/ Org. Chem.,... 

Oppenauer oxidation, 236 Oxidation of allylic alcohols with dichloro-dicyanobenzoquinone, 248 Oxidation of allylic alcohols with manganese dioxide, 247... 

Thus, reduction of androst-5-ene-l,17-dione (1-5) with lithium aluminum hydride reduced both 3- and 17-carbonyl groups, that at Cn cleanly to the /8-epimer and the ketone at C3 to a mixture of epimers (3-1) (Scheme 5.3). Treatment of the mixture of epimers with manganese dioxide oxidizes the allylic alcohol at C3, leaving that at C17 untouched, affording testosterone (3-2). 

Oxidation of cinnamyl alcohol with manganese dioxide in a suitable solvent (like hexane or octane) gives the corresponding aldehyde on sonication. It is believed that under sonication the low reactive manganese dioxide is activated. 

The synthesis of several terpenoid natural lactones has been described. Butyrolactones are formed efficiently by the cyclization of hydroxy-acids, and acid olefin cyclization. The diester (123) has been converted independently into the isomeric lactones cinnamolide (124), and drimenin (125) (Scheme 71). Selective reduction of the a,/3-unsaturated ester was used in the latter case, whereas selective oxidation of the corresponding allylic alcohol with manganese dioxide was used in the former. Manganese dioxide has also been... 

Other Anhydrides.—The enones (42) and (43) have been prepared by oxidation of the corresponding allylic alcohols with manganese dioxide. Whereas the oxiran derivative (44) afforded the allylic alcohol (45) on treatment with butyl-lithium, the /yxo-isomer (46) gave the 2-substituted glycal (47). Enols with equatorially oriented hydroxy-groups were obtained when the enones (42) and (43) were reduced with sodium borohydride. 

Selective Oxidation of a Benzylic Alcohol with Manganese Dioxide H OH... 

Preparation of Acrolein by Oxidation of Allyl Alcohol with Manganese Dioxide 2 ... 

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. 

Aldehyde 244 reacts with manganese dioxide and sodium cyanide in ethanol to give ethyl ester 245 (Scheme 19), while oxidation of alcohol 12 with sodium peroxodisulfate in the presence of a catalytic amount of ruthenium chloride furnishes the carboxylic acid 246 (Scheme 19) <1998CPB287>. 

It is of interest that the methyl alcohol 81 underwent oxidation with chromic acid to afford 3-acetylfervenulin 83 in good yield, whereas the same conditions resulted in the conversion of alcohol 79 into fervenulin 8. The desired product of this latter transformation, that is, fervenulin-3-carboxaldehyde 82, could, however, be obtained, albeit in low yield, by the oxidation of alcohol 79 with manganese dioxide. Fervenulin-3-carboxaldehyde 82 could be obtained in much better yield from the treatment of 3-styrylfervenulin 68 with periodate in the presence of osmium tetroxide, or by ozonolysis of the same substrate. 

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