Hydroxylation permanganate, olefin

Acetal formation is a characteristic property of aldehydes. It is.the addition of two alcohol molecules to the carbonyl carbon under acidic conditions. Acetals are stable to the hydroxylation of olefins by neutral permanganate in alkaline condition. It can be converted back to aldehyde by acid-catalyzed hydrolysis. However, the double bond has to be masked before the acetal formation. This can be done simply by hydrohalogenation which does not affect the aldehyde. Dehydrohalogenation can be accomplished by elimination after the formation of acetal. 

Hydroxyl.—At low temperature the olefines are converted into their glycols by permanganate ... 

Successive treatment of primary or secondary nitroalkanes with triethylamine and hex-adecyltrimethylammonium permanganate affords aldehydes or ketones, respectively (e.g. equation 129). Hydroxyl groups and olefinic double bonds are not affected421. 

Hydroxylation of the olefinic bond is also a convenient route for utilization of the alkenes being considered. Treatment of alkene 26 with aqueous alkaline potassium permanganate resulted in formation of compound 45, the structure of which was established by a de-gradative procedure11. It followed from this result that the initial alkene (26) was the cis isomer. Treatment of alkene 28d with iodic acid in the presence of a catalytic amount of osmium tetraoxide, with propyl alcohol as the solvent, led918 to a mixture of two alditols (46). 

Olefins can be easily oxidized to cis- 1,2-glycols by dilute potassium permanganate solutions.110 This reaction has been used for hydroxylation of numerous unsaturated compounds of the most diverse types.111... 

It is very important to choose the reaction conditions so as to avoid further oxidation of the glycols formed if, for instance, the permanganate is added too rapidly to a neutral solution of olefin, the main product is an acyloin RCH(OH)—COR. 112 Hydroxylation is usually effected in the cold with neutral or alkaline potassium permanganate solution water, acetone, alcohols, methylcyclohexane, and mixtures of alcohol and water can serve as solvent. Magnesium sulfate is often added for reactions in a neutral medium.113... 

The two racemic tetroses have been prepared from 43 by a sequence of reactions involving the extension of the carbon atom chain by a Grignard reaction with ethyl orthoformate to four atoms, acetylation, and half-reduction of the triple bond to a cis olefin (48). cw-Hyroxylation of 48 with potassium permanganate, peracetylation (for the purpose of isolation), and final hydrolytic deprotection gave DL-erythrose. franj-Hydroxylation of 48 with peroxyacids failed. Therefore acetal 48 was hydrolyzed with 70% aq. formic acid to 4-acetoxycro-tonaldehyde (49). Reacetalization of 49 followed by cii-hydroxylation led to dl-threose in about 14% yield. 

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