Silver carbonate on celite

Acknowledgment The authors wish to express their gratitude to Dr. J. Edwards of Syntex Research who provided the experimental procedure utilizing silver carbonate on Celite. We are also indebted to the Synthetic Chemical Research Department of Merck Sharp Dohme Research Laboratories for providing time to complete this review and also to Miss Joanna Mohr for her patience and care in preparing the manuscript. 

Concomitant protection of the amino group and the cis-hydroxyl group of the diol 342 was realized by treatment with formaldehyde to afford the oxazolidine 345, oxidation of which with silver carbonate on Celite gave the... 

Acyclic ADC compounds, which are more correctly named as derivatives of diazene, are generally prepared from hydrazine derivatives. For example, diethyl azodicarboxylate (Chemical Abstracts name diethyl diazene-1,2-dicarboxylate)5 is prepared from hydrazine by treatment with ethyl chloro-formate followed by oxidation with chlorine in benzene-water.6 Other oxidants which have been used include JV-bromosuccinimide,7 nitric acid,8 inorganic nitrates,9 potassium dichromate,10 silver carbonate on celite,11 and phenyl iodosotrifluoroacetate.12 The hydrazine derivative may also be... 

In contrast to the oxidation of acyclic polyhydric alcohols in benzene,508 treatment of 1,2-O-isopropylidene-a-D-glucofuranose with silver carbonate-on-Celite in boiling methanol led to selective oxidation of the primary hydroxyl group, with the formation of the al-duronic acid derivative in 68% yield.517... 

Additional activation of the 3-OH group by an allylic double bond increases the selectivity and leads to 50% testosterone (27). Cholic acid is oxidized exclusively at the 3a-position without any attack at the 7a- and 12a-hydroxy groups. Comparable selectivities have been reported for oxidations by silver carbonate on celite and by molecular oxygen with a platinum catalyst The yield of 23 is however lowered by a competing reaction to the lactone 24 this is formed by oxidative cleavage of the C3—C4 bond, followed by lactonization during work-up. 

S. Morgenlie, Isopropylidene derivatives of a-D-galatofiiranose, Acta Chem. Scand. 27 3609 (1973) S. Morgenlie, Oxidation of carbohydrate derivatives with silver carbonate on celite. X. Identification of three mono-O-isopropylidene derivatives of D-galactose, Acta Chan. Scand B 29 367 (1975) S. Morgenlie, Reaction of some aldoses with anhydrous cupric sulphate-acetone, Carbokydr. Res. 41 77 (1975). 

Silver carbonate on Celite has been the preferred reagent for this oxidation (3, 247), but 10-20 equivalents of oxidant is required. In addition the regioselectivity is highly dependent on the solvent. Thus 2 is oxidized by Fetizon s reagent in CH2C12/C6H6 to a 1 1 mixture of 3 and 4-ketopentanol-l (4), but in CHC13 to 3 and 4 in the ratio 9 1. 

The available experimental data4 are consistent with the following mechanism for the oxidation of alcohols with silver carbonate on Celite ... 

From 1 to 10 g (ca. 5-15 equivalents)—typically 3 g—of silver carbonate on Celite per mmol of alcohol are added to a ca. 0.01-0.15 M solution of the alcohol in drya benzene.b The resulting suspension is refluxed till most of the starting alcohol is consumed.0 The suspended solid is filtered, employing filter paper or a pad of Celite , and washed with benzene or other organic solvent. Concentration of the organic solution at the rotary evaporator yields the crude carbonyl compound that may need further purification. 

Phenols suffer oxidation to quinones and oxidative dimerizations under the action of silver carbonate on Celite .13... 

A corollary of this selectivity is the very easy transformation of diols into lactones with silver carbonate on Celite .16 During the oxidation of a diol with Fetizon s reagent, as soon as an intermediate hydroxyaldehyde is able to equilibrate with a certain proportion of hemiacetal—even if present... 

Halohydrins are transformed into epoxides or into transposed products on contact with silver carbonate on Celite .18... 

Oxidation.—Silver carbonate on celite (Fetizon s reagent) reacts non-selectively with a pregnane-18,20-diol (60), giving the lactone (6l) and the lactol (62).82 Special conditions have been described for the selective oxidation of 5a -androstane-3/3,6/3-diol with Fetizon s reagent to give the 3-oxo-derivative as major product. The 3/8,6a-diol readily gives the 3-oxo-derivative in good yield.83... 

In woric related to natural product synthesis the efficacy of silver carbonate on Celite was compared with a platinum-catalyzed oxidation using an oxygen atmosphere for the oxidation of (23 equation 26). In some cases the Pt/Oz system was superior, but in others the situation was reversed, with no obvious rationale. The Pt/02 reagent has been used in the total synthesis of the hydroazulene natural products damsin (24 Scheme 7), aromatin (25) and aromaticin (26 Scheme 8). ... 

The selective oxidation of diols in which one or both hydroxy groups are allylic has been reported on a number of occasions. Reagents which have proved use for this include silver carbonate on Celite, barium manganate/ and manganese dioxide, as illustrated in equations (29)-(31). 

A modification of the Oppenauer oxidation which uses trichloroacetaldehyde on alumina provides a good, general oxidation of alcohols, and in particular will oxidize a secondary akdiol in the presence of a primary one, as shown by the examples given in Scheme 16. This method is claimed to be superiw to silver carbonate on Celite and much cheaper. Other advantages of this method are that it is neutral, nonaqueous, and halide, ester and lactone functionalities survive the reaction conditions. ... 

Silver carbonate on Celite itself is a highly selective reagent for this type of chemoselective oxidation as can be seen from the examples in Scheme 17 secondary diols can be oxidized to the hydroxy ketones, and primary diols are oxidized to lactones (see Section 2.9.2.2). 

Methods of oxidation of hydrazo to azo compounds and hydroxylamino to nitroso compounds have been reviewed. Reagents which oxidize aromatic primary amines to azo compounds are also suitable for the oxidation of aromatic hydrazo compounds, since the hydrazo compounds are intermediates in the oxidation of the amines. Thus, manganese dioxide, mercury(II) oxide and lead tetraacetate are all suitable oxidants. Silver carbonate on Celite rapidly oxidizes both diarylhydrazines and acylhydrazines to the corresponding azo compounds in good yield. Another supported oxidant which can convert hy-drazobenzene into azobenzene in high yield is sodium periodate on silica gel. ... 

Aliphatic nitroso compounds can be prepared from IV-alkylhydioxylamines oxidation widi bromine, chlorine or sodium hypochlorite in weakly acidic solution, reaction with potassium dichromate in acetic or sulfuric acid, and by oxidation widi yellow mercury(II) oxide in suspension in an organic solvent. Silver carbonate on Celite has also been used to prepare aliphatic nitroso compounds, such as ni-trosocyclohexane, in high yield from the corresponding hydroxylamines." Aqueous sodium periodate and tetraalkylanunonium periodates, which are soluble in organic solvents, are the reagents most commonly used for the oxidation of hydroxamic acids and IV-acylhydroxylamines to acylnitroso compounds... 

Historically, the first supported oxidizing reagent, reported by Fdtizon and Golfier, was silver carbonate on celite (another diatomaceous earth). This was obtained by precipitation of the reagent onto its support. Ag2C03 on celite smoothly oxidizes primary and secondary alcohols, a,(o-diols, hydroquinones and amines. The main practical asset of the reagent is that it avoids the need to filter off finely divided silver salts after reaction. 

---