Oxidative cleavage with chromium reagents

The chiral Fischer-type chromium carbene complex of furan 28, shown in Scheme 14, participated in nucleophilic 1,4-addition with organolithium reagents followed hy alkylation in a regioselective and diastereoselective manner, creating a quaternary C-3 stereocenter in the 2,3-trisubstituted 2,3-dihydrofuran products after oxidative decom-plexation and reductive cleavage of the chiral auxiliary <2003CEJ5725>. 

Oxidative cleavage of cyclopropanes has been studied mostly with lead(IV), thaIlium(III) and chromium(Vl) reagents. - The oxidative cleavage of cyclobutanols has been explored mainly with chro mium(VI) reagents, although other oxidants have been studied. ... 

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]. 

It is now generally admitted that this reaction involves both one-electron and two-electron transfer reactions. Carbonyl compounds are directly produced from the two-electron oxidation of alcohols by both Crvl- and Crv-oxo species, respectively transformed into CrIV and Crm species. Chromium(IV) species generate radicals by one-electron oxidation of alcohols and are responsible for the formation of cleavage by-products, e.g. benzyl alcohol and benzaldehyde from the oxidation of 1,2-diphenyl ethanol.294,295 The key step for carbonyl compound formation is the decomposition of the chromate ester resulting from the reaction of the alcohol with the Crvl-oxo reagent (equation 97).296... 

Cyclobutanols oxidize with ring cleavage to 4-hydroxy ketones, 4-hydroxy acids, or 1,4-diones under the influence of chromium(Vl) reagents (Scheme 11). The first formed product is a 4-hydroxycarbonyl compound (31) which exists as the five-membered ring hemiacetal (32). This form will persist in the absence of excess reagent under nonforcing conditions otherwise further oxidation takes place to give a... 

Two oxidants essentially dominate these oxidations lead tetraacetate in organic solvents and periodic acid in aqueous media. On occasion, other oxidation reagents cause the cleavage of vicinal diols ceric ammonium nitrate [424], sodium bismuthate [482, 483], chromium trioxide [482, 555], potassium dichromate with perchloric acid [949], manganese dioxide [817], and trivalent [779, 789] or pentavalent [798] iodine compounds. 

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