Sarett reagent

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. 

CrOs-pyridine complex The oxidation of alcohols to aldehydes and ketones with CrOs in the presence of pyridine solvent is known as the Sarett oxidation. Sarett used the CrOs-pyridine complex in the synthesis of steroids. Although primary alcohols give poor yield, benzylic, allylic and secondary alcohols give good yields with Sarett reagent. 

Oxidation of akohois. The oxidation of alcohols with the reagent is conducted in methylene chloride with a sixfold molar excess of oxidant. The oxidation usually proceeds to completion in 3 -13 min. at 23°. The reagent is particularly recommended for oxidation of primary alcohols to aldehydes in this case use of the Sarett reagent (1,145 -146 2,74-75) usually gives low yields. Thus 1-heptanol can be oxidized by the Collins reagent in methylene chloride to l-heptanal in 70-84% yield. 

Saligenin, 719 Sandmeyer reaction, 1098 Santonin, 19, 608 (—)-j8-Santonin, 995 Sarcosine methyl ester, 1160 Sarett reagent, 145-146 Schiff bases, 139, 273, 318, 428, 430, 746, 788, 885 reduction, 1230 Schiemann reaction, 394,1140 Scopoletin, 790 ScylUtol, 1209 Sebacamide, 1265 Sebadc acid, 584, 1265 Sebadl, 159... 

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. 

Oxidation of cammaconine with Sarett reagent afforded two products, dehydro-oxocammaconine (23) and didehydro-oxocammaconine (24). Both products showed spectral characteristics for two methoxy-groups, an AT-ethyl group, a hydroxy-group, a cyclopentanone moiety, and a tertiary lactam in a six-membered ring. The second product also possessed an i.r. absorption band characteristic of a cyclohexanone. There was no evidence of an aldehyde proton in the n.m.r. spectra of either product. 

Compound CLVIII was further characterized by oxidation with Sarett reagent and the resulting C-3 ketone (CLXII) was refluxed in methanolic... 

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... 

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