Glycols cleavage, oxidative

MALAPRAOE LEMIEUX JOHNSON Olefin (dfoO cleavage Oxidative cleavage of 1,2-glycols to two cart nyls (Malaprade) or direct oxidation o( olefins IO4 and OSO4 catalyst (Lenveux Johnson)... 

The reaction is based, on the one hand, on the oxidative cleavage of vicinal diols by lead(IV) acetate and, on the other hand, on the reaction of dichlorofluorescein with lead(IV) acetate to yield a nonfluorescent oxidation product. The dichlorofluorescein only maintains its fluorescence in the chromatogram zones where the lead(IV) acetate has been consumed by the glycol cleavage reaction [1],... 

Fatty acids, both saturated and unsaturated, have found a variety of applications. Brassilic acid (1,11-un-decanedicarboxylic acid [BA]), an important monomer used in many polymer applications, is prepared from erucic acid (Scheme 2), obtained from rapeseed and crambe abyssinica oils by ozonolysis and oxidative cleavage [127]. For example, an oligomer of BA with 1,3-butane diol-lauric acid system is an effective plasticizer for polyvinylchloride. Polyester-based polyurethane elastomers are prepared from BA by condensing with ethylene glycol-propylene glycol. Polyamides based on BA are known to impart moisture resistance. 

Desilylation of the major jjw-isomer, followed by oxidative cleavage with sodium metaperiodate, liberates the 3-hydroxy-2-methyl carboxylic acids. The immolative character of this method, i.e., the destruction of the chiral auxiliary reagent in the final glycol cleavage, is a drawback. 

Cyelobutanone has been prepared by (1) reaction of diazomethane with ketene,4 (2) treatment of methylenecyclobutane with performic acid, followed by cleavage of the resulting glycol with lead tetraacetate,s (3) ozonolysis of methylenecyclobutane, (4) epoxidation of methylene-cyclopropane followed by acid-catalyzed ring expansion,7 and (5) oxidative cleavage of cyclobutane trimethylene thioketal, which in turn is prepared from 2-(co-chloropropyl)-l,3-dithiane.8... 

It is an important reagent for the oxidative cleavage of vicinal glycols which are oxidised at room temperatures to aldehydes, ketones or both depending on the nature of glycol. 

As discussed in connection with cleavage of double bonds by permanganate-periodate or osmium tetroxide-periodate (see p. 757), the glycol unit is susceptible to oxidative cleavage under mild conditions. The most commonly used reagent for this oxidative cleavage is the periodate ion.150 The fragmentation is believed to occur via a... 

Exposure of 144 to catalytic quantities of ruthenium tetroxide, generated in situ from ruthenium trichloride and sodium periodate, produces the symmetrical lactones 145 <2000JA9558>. It is proposed that the products form as a result of the ruthenium-catalyzed oxidative cleavage of the a-diketones to produce intermediate glycols (Equation 49). 

With respect to the side chain, although some standard reactions failed [78], different correlation reactions assayed to confirm the structure of new isolated members were achieved successfully, some examples include oxidation of the podolactone C sulphoxide group to give the corresponding sulphone (110), as well as the glycol oxidative cleavage of... 

Another is the oxidation of a secondary alcohol to a ketone (9-3), where A and B are alkyl or aryl groups and Z is also CrOjH. In the lead tetraacetate oxidation of glycols (9-7) the mechanism also follows this pattern, but the positive leaving group is carbon instead of hydrogen. It should be noted that the cleavage shown is an example of an E2 elimination. 

Oxidative Cleavage of Glycols and Related Compounds 21O-De-hydrogen-uncoupling... 

With a molar ratio of propylene glycol to H2O2 of 2.5, the selectivity to hydroxyacetone at 32% conversion of the glycol was 94%, and the selectivity based on H202 was 85%. Small amounts of acetic acid and formic acid were detected. The initial oxidation proceeds with high selectivity for the secondary alcohol group. Further oxidation affords oxidative cleavage products rather than pyruvic acid, as is observed when the oxidation of hydroxyacetone is carried out with 02 and noble metal catalysts. 

Oxidative cleavage of the olefin is accomplished by the method of ijemieux-Johnson.12 The process begins with dihydroxylation of the double bond using osmium tetroxide (see Chapter 3)T leading to a cis diol and osmium(VI) oxide. The added periodate has two functions first, it reoxidizes the osmium(VI) species to os-mium(VIII), but it also cleaves the glycol oxidatively to an aldehyde. This is the reason for utilizing several equivalents of periodate. The periodate is in turn reduced from the +VH to the +V oxidation state. 

Oxidation of glycol esters to ene-S-lactones. Reaction of glycal esters with m-chloroperbenzoic acid involves the expected epoxidation followed by cleavage of the oxide by the /n-chlorobenzoic acid formed. However, in the presence of BF3, the reaction produces a,/ -unsaturated 5-lactones, usually in excellent yield. This oxidation is also possible with pyridinium chlorochromate and BF3 as catalyst, but in lower yield.1... 

The reagent is effective for oxidative cleavage of a-glycols to aldehydes, of a-hydroxy ketones to an aldehyde and a carboxylic acid, and of a-diketones and a-keto iicids to acids.3... 

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