1,2-Diols chromium oxides

Some more recent processes have been developed which involve direct hydrogenation of the oil to the fatty acid and 1,2-propane diol. These high-temperature (>230 °C) and high-pressure processes generally use a copper chromium oxide catalyst. 

The reduction into diols is performed by using KBH4 [68], AlLiH4 [69, 70] and also by catalytic reduction (copper and chromium oxide) [68] or Ru/C [71]. 

The reduction of aldols and ketols from the aldol condensation (method 102) is often a convenient route to branched 1,3-dio/s. Catalytic hydrogenation over platinum oxide, nickel-on-kieselguhr, and copper-chromium oxide has been used. Other procedures include electrolytic reduction and reduction by aluminum amalgam. 1,3-Diols may also be prepared by catalytic reduction of 1,3-diketones. Cleavage of the carbon-to-carbon and carbon-to-oxygen bonds accompanies this conversion. The effect of structure on the course of the reaction has been studied. ... 

Oxidation of quinazolin-4(3/f)-one to quinazoline-2,4(l/f,3f )-dione with chromium(VI) oxide or potassium permanganate yields only traces of the product and is therefore preparative-ly not important. However, oxidation of quinazolin-4(3/f)-onc 1-oxide with chromiurn(VI) oxide in glacial acetic acid affords l-hydroxyquinazoline-2,4(l//,3//)-dione which is tautomeric with quinazoline-2,4-diol 1-oxide (50%). ... 

Carbonyl groups. Breitner et al. found Engelhard Ru-C and Rh-C distinctly superior to Pl-C and Pd-C for the hydrogenation of ketones in neutral or basic medium. Hu.sek et til. iittcmpted reduction of tetramothy 1-1,3-cyclobutanedione with platinum, palladium, and rhodium catalysts but the results were very poor. With copper-chromium oxide and supported nickel culitlyilR yieldsol diols were moderate,... 

Cholestane-3/3,5a-diol 3-acetate, 397 Cholestane-4a,5a-diol 4-tosylate, 398 Cholestane-5a,6a-diol 6-tosylate,394 5a-Cholestan-2-one, 57, 88, 427 10(5 4 H)ijAeo-Cholestan-5-one, 398 10(5 6)ij ieo-Cholestan-5-one, 392, 394 5a-Cholestan-3-one cyanohydrin, 359 5a-Cholestan-3-one cyanohydrin acetate, 360 5a-Cholestan-2a,3a-oxide, 42 5a-Cholestan-2/3,3/3-thiirane, 43 Cholest-5-ene-3, 19-diol, 268 Cholest-5-ene-3, 25-diol, 71 5(10->l/3H)flfc eo-cholest- 10(19)-ene-3/8,5a-diol 3-acetate, 397, 398 Cholest-4-ene-3,6-dione, 105 Cholest-4-en-3-one, 318 Chromium trioxide, 147, 150 5a-Conanine-3/3-ol-ll-one 3-acetate, 259 Cupric bromide, 210, 211 Cuprous chloride-catalyzed conjugate addition, 76, 80... 

Addition of 4-pentenyllithium to the dione 65 gave the ds-diol 71 which was converted to the (Z)-l,2-disubstituted cyclododecene 72a. Hydroboration-oxidation and chromium trioxide oxidation provided the dialdehyde 72b whose McMurry ring closure, followed by partial catalytic hydrogenation gave the (Z)[10.10] precursor 73. Treatment of this (Z)-olefin 73 with HzS04-Ac0H in benzene was reported to effect conversion into [10.10]betweenanene (61b) of 95% purity and high yield. 

A selection of cases in which 2 has been found to be particularly efficacious is given in the Table. Additional examples are cited in references 1 and 5. Particularly noteworthy examples include the oxidation of acid- and base-sensitive systems, systems containing sulfur and selenium, and 1,3-diols to 1,3-dicarbonyl compounds. Use of chromium reagents in these latter cases often leads to fragmentation products. 

The oxidation of chroman-4-ols to chroman-4-ones, on the other hand, is more easily accomplished, using chromium trioxide in acetic acid (66JCS(C)2013). The same oxidant in pyridine converts chroman-3,4-diols to the 3-hydroxychroman-4-one (65CB1498). 

Using chromium-based oxidants 2,4-Dimethylpentane-2,4-diol chromate(VI) diester, 122 Trimethylsilyl chlorochromate, 327 Using other oxidizing agents... 

Using chromium-based oxidants 2,4-Dimethylpentane-2,4-diol chromate(VI) diester, 122 Trimethylsilyl chlorochromate, 327 Using other oxidizing agents Bis(tributyltin) oxide, 41 Hydrogen hexachloroplatinate(IV)-Copper(II) chloride, 145 4-Methoxy-2,2,6,6-tetramethyl-1 -oxopiperidinium chloride, 183 Osmium tetroxide, 222 Potassium nitrosodisulfonate, 258 Samarium(II) iodide, 270 From alkenes by addition or cleavage reactions... 

Chromium coordinates selectively with the 1,2-diol, forming a stable cyclic chromate ester that evolves producing the formation of a tetrahydrofuran. Observe that no formation of tetrahydrofuran from the alcohol on the left occurs, for this would involve the intermediacy of a less stable simple chromate ester (vide infra). The experimental conditions are so mild that no direct oxidation of the secondary alcohol to ketone is observed, either on the starting compound or in the product. 

This mechanistically fascinating product can be explained by the initial formation of a cyclic chromate ester, facilitated by the formation of a five-membered ling and the (cis) relationship in the 1,2-diol. Interestingly, this stable chromate does not evolve resulting in the oxidation of the secondary alcohol, but it suffers elimination producing a very electron-rich benzyloxy alkene that is easily epoxidized intramolecularly by chromium. Observe that the epoxide oxygen enters from the same face than the secondary alcohol. 

In variance with other oxidants, such as the chromium-based ones, no carbon-carbon bond breakage is observed in the Pfitzner-Moffatt oxidation of this 1,2-diol. 

The mixture 258 was converted to the unstable benzenesulfonyl aziridine 259 by treatment with an excess of benzenesulfonyl azide in benzene. Ace-tolysis of 259 with acetic acid and sodium acetate at room temperature for several days afforded the crystalline mixture of diastereoisomers represented by the formula 260. The aziridine rearrangement was regiospecific and 260 was the only product detected during this rearrangement. Lithium aluminium hydride reduction of 260 followed by acetylation yielded the mixture 261 in 85% yield. Selective hydrolysis of 261 afforded 262 in quantitative yield. The diastereoisomeric mixture 262 was converted into the diols 263 by hydrogenolysis. The diol mixture was oxidized with chromium trioxide... 

---