Chromium dimethylpyrazole

Allylic oxidations may also be carried out with the related Chromium(Vl) Oxide-3,5-Dimethylpyrazole (DMP) complex.3... 

Chromium(II) complexes of the ligands l,l -methylenedipyrazole (11 H2Cpz2), l,l -methyl-enebis(3,5-dimethylpyrazole) (12 H2Cdmpz2), tris(l-pyrazolyl)methane (13 HCpz3),10S tris(l-pyrazolylethyl)amine (14 R = H, TPyEA)106,107 and tris(3,5-dimethyl-l-pyrazolylethyl)amine... 

With the advent of the chromium trioxide-3,5-dimethylpyrazole complex as an oxidant - allylic oxidation has become far more valuable as a synthetic transfonnation. The reagent was applied by Sala-mond to the allylic oxidation of cholesteryl benzoate to give the correspondbg A -7-ketone (equation 35). However, a 20 molar excess of reagent was still requii to effect the reaction in less than 30 min at room temperature. 

Some fine examples of the synthetic use of this reagent are available in the literature for example in a total synthesis of vemolepin, intermediate (70), containing a fairly sensitive lactol ether unit, was selectively prepared by the use of chromium trioxide-dimethylpyrazole with formation of only 5% of the allylically rearranged product (equation 36). 

Although chromium(VI) oxide-(3,5-dimethylpyrazole) is also a good oxidant for allylic C—bonds, it is surprising that this reagent has not been more widely adopted. 

Two independent syntheses of quadrone eiiq>loyed an allylic oxidation with rearrangement, as shown in equation (3), where the chromium trioxide-(3,5-dimethylpyrazole) reagent (CrOs DMP) was used. In some cases, the success of the reaction strongly depends on the nature of the oxidant, as shown in an iq>proach to (-)-upial (equation 4). Here the chi ium trioxide-heterocycle reagents, which are weaker oxidants, are quite inferior compared to the Fieser reagent ... 

Chromic acidarui simple chromate esters 2.13.1.2 Pyridinium chlorochromate and dichromate 2.13.13 Chromium trioxide-33-dimethylpyrazole... 

In contrast to the Collins reagoit, the complex formed by 3,5-dimethylpyrazole with chiomium(VI) oxide (2) is very soluble in dichloromethane. Hence, reactions (up to 0.1 mol scale) can be carried out in the minimum amount of solvent. Generally, 2.5 equiv. of complex, generated in situ, gives good yields of aldehydes and ketones. In addition, upon woric-up most of the chromium salts may be precipitated by dilution with diethyl ether. 

Chromium trioxide-3,5-dimethylpyrazole complex, Cr03 CsHgN2, is... 

Instead of pyridine, 3,5-dimethylpyrazole may be used for complexing chromium trioxide. It forms a l.T complex that can be generated in situ in dichloromethane at room temperature. The reaction is finished within 10 min. Addition of the alcohols and stirring of the mixture for 30 min at room temperature result in 78-100% yields of ketones (equation 252) 602. ... 

Chromium trioxide-3,5-dimethylpyrazole is a mild and selective reagent for oxidation of a-methylenecyclopropanes into cyclopropylketones <93CC954>. 

Pyrazole-tethered Schiff base ligands 62 promoted Suzuki cross-couplings of aryl bromides and chlorides with phenylboronic acid efficiently under mild conditions <05TL15>. Chromium-trioxide complex with 3,5-dimethylpyrazole 63 oxidation of cyclohexenecarbonitrile provided 3-oxocyclohex-1 -ene-1 -carbonitrile <05S3179>. 

The chromium trioxide-3,5-dimethylpyrazol complex has been found to be a mild and selective reagent for the oxidation of cyclopropyl hydrocarbons (reaction proceeds in the dark at -20 °C) [67]. 

Cholestanone, 497 5a-Cholestanone, 475 A -Cholestene, 497 A -Cholestene-3d,5a-diol, 110 A -Cholestene-3/3,5(3-diol, 110 Cholesteryl benzoate, 110 Chromenes, 235-236 A -Chromens, 407 Chromic acid-Silica gel, 110 Chromic anhydride-3,5-Dimethylpyrazole complex, 110 Chromium carbonyl, 110 Chromium(III) chloride-Lithium aluminum hydride, 110-112 Chromyl chloride, 112 ... 

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