Lead tetraacetate amides, oxidation

The earliest oxidations were effected with nitrous fumes and later with mercuric oxide and isoamyl nitrite.74 Lead tetraacetate in acetic acid is in many cases the reagent of choice, but the removal of by-products can present some difficulties.75 IV-Haloimides and amides in alcoholic solutions have been reported to yield essentially pure tetrazolium salts76 and have been found specially useful in the preparation of heteroaryl-substituted tetrazolium salt.77,78 The novel formazans 49 have been successfully oxidized to 50 using 7V-chloro succinimide (Eq. II).79 tert-Butyl hypo-... 

Treatment of amides with bromine in alkaline medium promotes the Hofmann rearrangement, which may or may not involve a free nitrene intermediate." The oxidation of primary amides with lead tetraacetate and the resulting Lossen rearrangement also produces isocyanates, with the possible intervention of an acylni-... 

An extremely interesting and novel method has been described (91TL133). The principle involved is the intramolecular Diels-Alder addition of a 2,4-dienoic acid amide with an azodicarbonyl moiety. /V-Sorbyl-proline (27) was condensed with an acylhydrazine to form (28). Oxidation of this with lead tetraacetate (LTA) in boiling benzene resulted in the piperazinedione (30). This must have come about via (29), which could undergo an intramolecular Diels-Alder reaction. The structure and stereochemistry of (30) were confirmed by X-ray crystallography. The two new chiral centers have the R configuration as shown in (Scheme 9). 

Determination of the structure of an amide of a carbohydrate is not difficult. Examination of acyl derivatives indicates whether a cyclic or an acyclic structure is present. Moreover, the results of oxidations with periodate and lead tetraacetate allow unequivocal determination of these structures alternatively, methylation studies have been used. 

Oxidation of amides. Primary amides are oxidized to isocyanates by lead tetraacetate at 5CV-60 in DMF or benzene in a Hofmann-like reaction. ... 

The oxidation of primary amides with lead tetraacetate gives isocyanates, when carried out in dimethylformamide carbonates, when carried out in the presence of alcohols and ureas, when carried out in the presence of amines (equation 482) [1182]. 

Closely related to the arsine oxide method is a ready way for preparing arsinimines by heating together triphenylarsine, an amide and lead tetraacetate in a one-pot reac-... 

The characterization of polymer chemical composition is important in numerous practical applications. The polymer identification can be done using various techniques. One of them is the chemical method, which involves reagents that are able to react with the polymer. Oxidation, for example using periodic acid or lead tetraacetate, can be applied to polymers containing 1,2 diol groups, ozonolysis can be applied to polymers containing double bonds, hydrolysis can be applied to esters and amides [4]. 

HETEROCYCLES Copper phcnylace-tylide. Dichlorobis(benzonitrile)palladium. N-Dichloromethylene-N,N-dimcthylammo-nium chloride. Diiminosuccinonitrile. Dimethyl acetylenedicarboxylate. Dipotassium cyanodithioimidocarbonate. Ethoxy-carbonyl isothiocyanate. Ethyldiisopropyl-amine. Ethylene oxide. Hydrogen fluoride. Isocyanomethane-phosphoric acid diethyl ester. Lead tetraacetate. Lithium aluminium hydride. Methylhydrazine. Phosphoryl chloride. Polyphosphate ester. Polyphosphoric acid. Potassium amide. Potassium hydroxide. Tolythiomethyl isocyanide. Tosylmethyl isocyanide, Trichlo-romethylisocyanide dichloride. Trimethyl-silyldiazomethane. 

Oxidative rearrangement. A reaction related to the Hofmann rearrangement of N-hromoamides occurs on oxidation of an aromatic amide with lead tetraacetate lo give the isocyanate or a derived product in moderate to excellent yield. Simple aliphatic amides react rapidly in dimethylformamide containing triethylamine. 

Oxidation of hydrocarbons with a tertiary carbon, e.g. adamantane, with lead tetraacetate in trifluoroacetic acid-dichloromethane solution, in the presence of chloride ion, gave high yields of trifluoroacetate functionahzed bridgehead alcohols [57]. Subsequent hydrolysis yielded the free bridgehead alcohols (Scheme 13.34). Another important advantage of this method is the feasible conversion of the intermediate trifluoroacetate into an amide with acetonitrile. 

Relatively few reactions of quinoxaline derivatives occur with change of ring size. Isolated examples are noted in the following text. For example, ring contraction to benzimidazole derivatives occurs when 2,3-diphenylquinoxaline (Chapter XV) or 2-halogenoquinoxalines (Chapter X) are treated with potassium amide in liquid ammonia and quinoxalin-2-one is treated with hydrazine (Chapter VX It is also found that oxidation of l-aminoquinoxalin-2-ones with lead tetraacetate give benzo-1,2,4-triazines (Scheme 6) (Chapter V). 

The pyrrole 23 was also oxidized to 26 using nitric acid, chromium(VI) oxide, lead tetraacetate in acetic acid, or phosphorus pentachloride in phosphorus oxychloride followed by hydrolysis in yields of up to 63%. However, hydrogen peroxide in acetic acid gave a mixture of the epoxy ketone 29 and the amide 30 29 was converted to 30 with ammonia, possibly via rearrangement of an intermediate (31)42 Oxidation of the N-methyl derivative of 23 gave pyrrolenineonium salts, which were difficult to purify.42... 

Rearrangement of amides. Primary amides undergo oxidative rearrangement to isocyanates when treated with lead tetraacetate. The reaction is generally carried out in an alcohol (t-butanol generally), in which case the product is isolated as the carbamate. Triethylamine or stannic chloride catalyzes this reaction. This oxidation provides a useful alternative to the classical Hofmann, Schmidt, and Curtius rearrangements. 

The perfection of this strategy makes use of the L-threonine-derived 2S,ZR acid 61 and tert-h xiy iV-(p-methoxybenzyl)glycinate as the active methylene partner [28d]. After condensation to amide 62, base treatment (LHMDS) induced epoxydation (at 0 °C) and then (25 °C) cyclization. This double inversion mechanism produced a single epimer, 63a, which, through acid 63b, was converted to target 11 by silylation, ester hydrolysis, lead tetraacetate and CAN (or peroxydisulfate) oxidation. 

C-N-0-CHj Oxidation of the parent JV-methoxy amide with lead tetraacetate/ Benzene EPR/ 350 2.0060 N 1.04 3H(CH3) 0.47 79For3... 

Kavirayani R. Prassad s elegant brevicomin synthesis starts also from tartaric add, although actually from its Weinreb amide, which is converted into the desired intermediate hy a double Grignard reaction. Other key steps in the synthesis are the lead tetraacetate-mediated cleavage of the diol and the Wacker oxidation of the terminal alkene. [204]... 

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