Sarett reagent preparation

Snatzke has found that a solution prepared from chromium trioxide and dimethylformamide with a small amount of sulfuric acid has similar chemical properties as the Sarett reagent. It is useful with acid sensitive compounds and oxidation occurs at such a moderate rate that selective oxidations are often possible. Although the position allylic to a A -double bond is not attacked, the 3-hydroxy-A -system cannot be oxidized satisfactorily to the cor-... 

Oxidation of veatchine (48) with Sarett reagent gave veatchinone (53), which, when reduced with NaBD4 in CH3OH, afforded an epimeric mixture of (54) and (55). This mixture was acetylated with acetic anhydride in pyridine and the acetates, (56) and (57), were separated by preparative-scale t.l.c. Treatment of (56) with 10% HC1 and re-acetylation gave (58). The 13C n.m.r. data indicated that there was no deuterium present at C-16 in (58) therefore, this rearrangement did not take place by a 15 —> 16 hydride shift. 

Cr03-pyridine complex (Sarett reagent), 1, 145-146 2, 74-75. Ratcliffe and Rodehorst4 find that the reagent can be prepared in situ directly in methylene chloride. Chromium trioxide (60 mmol.) is added to a stirred solution of pyridine (120 mmol.) in methylene chloride. The deep burgundy solution is stirred for 15 minutes at room temperature and then a solution of the alcohol (10 mmol.) in methylene chloride is added. A black deposit separates, and the product is isolated from the filtrate. One main advantage is that the complex can be prepared safely in this way without fire hazard. 

Oxidizing agent.1 Pyridine dichromate is similar to the Sarett reagent (1, 145-146) but has the advantage that the preparation is relatively safe. It is used in the same way and yields are comparable. 

A modification was introduced by Collins et al., and when applied to the oxidation of alcohols it has come to be known as Collins oxidation. This modification was developed to circumvent the danger inherent in preparing the reagent, deal with the problem of poor yields in the oxidation of primary alcohols to aldehydes, and facilitate isolation of the carbonyl products. The Sisler-Sarett reagent formed by reaction of chromium trioxide and pyridine was first removed from the pyridine solvent and added to dichloromethane, and this mixture was then treated with the alcohol. The oxidation typically required a 5 1 or 6 1 ratio of complex/alcohol, and reaction occurred at ambient temperatures. Cyclohexanol was oxidized to... 

Sarett and coworkers discovered that the complex (1) prepared by the addition of chromium(VI) oxide to pyridine (CAUTION—reverse order of addition may cause the mixture to inflame) is an efficient oxidizing agent for the preparation of ketones from secondary alcohols. The reagent, as prepared by Sarett, is moderately soluble in pyridine, but is only sparingly soluble in standard organic solvents. Thus the normal procedure is to add a solution of the dcohol in pyridine to three equivalents of the complex, also in pyrictoe. This procedure is also useful for the preparation of aromatic and a, -unsaturated aldehydes, but the use of pyridine as solvent prohibits the oxidation of volatile, saturated primary alcohols. ... 

Sarett et al. worked out an improved method of preparation and used the reagent for the synthesis of cortisone 21-phosphate. Zervas describes other examples of use as a phosphorylating agent. 

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