Chromium trioxide-pyridine complex oxidant

A recently discovered (2) oxidizing system promises to become very important for the oxidation of acid-sensitive compounds. The reagent is chromium trioxide-pyridine complex, which may be isolated after preparation and employed in nonaqueous solvents (usually methylene chloride). A remarkable feature of the reagent is that good yields of aldehydes are obtained by direct oxidation of primary alcohols. The preparation of the reagent and its use are given. 

D. Oxidation with Chromium Trioxide-Pyridine Complex General Procedure... 

A 5% solution of chromium trioxide-pyridine complex in dry methylene chloride is prepared. The alcohol (0.01 mole) is dissolved in dry methylene chloride and is added in one portion to the magnetically stirred oxidizing solution (310 ml, a 6 1 mole ratio) at room temperature. The oxidation is complete in 5-15 minutes as indicated by the precipitation of the brownish black chromium reduction products. The mixture is filtered and the solvent is removed (rotary evaporator) leaving the crude product, which may be purified by distillation or recrystallization. Examples are given in Table 1.1. 

OXIDATION WITH THE CHROMIUM TRIOXIDE-PYRIDINE COMPLEX PREPARED in situ ... 

CHROMIUM TRIOXIDE-PYRIDINE COMPLEX, preparation in situ, 55, 84 Chrysene, 58,15, 16 fzans-Cinnamaldehyde, 57, 85 Cinnamaldehyde dimethylacetal, 57, 84 Cinnamyl alcohol, 56,105 58, 9 2-Cinnamylthio-2-thiazoline, 56, 82 Citric acid, 58,43 Citronellal, 58, 107, 112 Cleavage of methyl ethers with iodotri-methylsilane, 59, 35 Cobalt(II) acetylacetonate, 57, 13 Conjugate addition of aryl aldehydes, 59, 53 Copper (I) bromide, 58, 52, 54, 56 59,123 COPPER CATALYZED ARYLATION OF /3-DlCARBONYL COMPOUNDS, 58, 52 Copper (I) chloride, 57, 34 Copper (II) chloride, 56, 10 Copper(I) iodide, 55, 105, 123, 124 Copper(I) oxide, 59, 206 Copper(ll) oxide, 56, 10 Copper salts of carboxylic acids, 59, 127 Copper(l) thiophenoxide, 55, 123 59, 210 Copper(l) trifluoromethanesulfonate, 59, 202... 

Oxidation, of primary alcohols to aldehydes, 52, 5 of terminal olefins with chromyl chloride, 51, 6 of 2,4,4-trimethyl-1-pentene with chromyl chloride, 51, 4 with chromium trioxide-pyridine complex, 52, 5... 

The Collins/Sarett oxidation (chromium trioxide-pyridine complex), and Corey s PCC (pyridinium chlorochromate) and PDC (pyridinium dichromate) oxidations follow a similar pathway as the Jones oxidation. All these oxidants have a chromium (VI), normally yellow, which is reduced to Cr(IV), often green. 

III. Chromium VI Reagents / 227 Chromium Vi-acetic acid / 227 Chromium Vl-acetone / 228 Chromium trioxide-pyridine complex / 229 Chromic acid-dimethylformamide / 231 Two-phase oxidations / 232... 

The chromium trioxide-pyridine complex affords fair yields of dicarbonyl compounds by oxidation of suitably protected precursors 2,3 4,5-di-<3-isopropylidene-(2/f/e/n f/o-/l-D-(2ra/)/rtrt-hcxos-2-ulose-2,6-pyranose was thus prepared in 53% yield from 2,3 4,5-di-0-isopropylidene-/f-D-fructo-... 

Pyridinium chlorochromate, described as a safe, stable, and readily prepared alternative to the chromium trioxide-pyridine complex, is a convenient oxidant for primary and secondary alcohols84 and should find use in steroid chemistry. Dimethyl sulphide ditriflate , prepared from DMSO and trifluoromethanesulphonic anhydride at —78°C, has been used to oxidize 3-hydroxy-steroids.85 The biological... 

The discovery of the chromium trioxide-pyridine complex led to die accessibility of allylic oxidation under much less harsh conditions, typically room temperature reaction in (Uchloromethane solution " ... 

An alternative mechanism has also been proposied in which oxidation at the double bond leads to a ketol derivative, elimination of water from which then gives the unsaturated ketone (Scheme 18a)." Limited kinetic data are available and suggest that Scheme 17 is obtained for chromic acid oxidations. The discovery of the chromium trioxide-pyridine complex led to the accessibility of allylic oxidatitm under much less harsh conditions, typically room temperature reaction in dichloromethane solution ... 

An attempted allylic oxidation of (68 equation 29) was found by Paquette to be difficult to achieve using a range of reagents due to problems with polymerization and rearrangement. The chromium trioxide-pyridine complex was the only reagent combination found to be successful, albeit in low yield. 

An alternative to the chromium trioxide- yridine complex i provided by pyridinium chlorochromate (PCC) and pyridinium dichromate (PDC). These reagents, now ubiquitous for chromate-based oxidation of alcohols, overcome the hygroscopic nature of the chromium trioxide-pyridine complex and are prepared by a less hazardous procedure both are commercially available as are several other derivative reagents. 

The chromium trioxide-pyridine complex is a highly selective oxidant for alcoholic groups [28]. A mechanism similar to that discussed above seems possible, the selectivity being due to lowered reactivity of chromium trioxide in the pyridine complex. The remarkably smooth and selective oxidation of alcohols by chromium trioxide-sulphuric acid (Jones reagent) in acetone solution [2g] has not been explained. 

Conjugated acetylenic ketones can be prepared in about 40% yield by oxidation of alkynes with chromium trioxide-pyridine complex ... 

A - -Steroid. Dauben and Fullerton chose the following route for conversion of A -androstenc-.3)S,17 -diol diacetate (1) into A - -androstadiene-3, 17 -diol diacetatc (4). The starting material was converted into the 7-ketonc (2) by oxidation with chromium trioxide-pyridine complex in methylene chloride (2, 74 75). The ketone OAc... 

Oxidation. The chromium trioxide-pyridine complex is conveniently and safely prepared from the components in dichloromethane this solution readily oxidizes alcohols to give aldehydes or ketones. The complex has more vigorous oxidizing properties in acetic acid. " Primary and secondary alcohols are... 

OXIDATION WITH CHROMIUM TRIOXIDE-PYRIDINE COMPLEX... 

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