Oxidation of semicarbazide

Similarly, Compound I-inediated oxidation of semicarbazide should give oxidation product (s) equally reactive toward a proximal nucleophile. 

Second, under nonturnover conditions, with preformed compound I, the oxidation of semicarbazide is accompanied by uptake of oxygen (118b), suggesting the formation of an intermediate such as diimide (123, 124), followed by its autoxidation [cf. Eq. (6)]. In a parallel reaction with AT, no uptake of oxygen is to be expected, and none is obtained (118b). 

A facile method for the synthesis of azoalkanes has been reported direct oxidation of semicarbazides with copper(ii) chloride complexes affords the base-labile m-azoalkane-copper(i) chloride complexes and isocyanates (Scheme 156). 

C ( propyl) N phenylmtrone to N phenylmaleimide, 46, 96 semicarbazide hydrochloride to ami noacetone hydiochlonde, 46,1 tetraphenylcyclopentadienone to diphenyl acetylene, 46, 44 Alcohols, synthesis of equatorial, 47, 19 Aldehydes, aromatic, synthesis of, 47, 1 /3-chloro a,0 unsaturated, from ke tones and dimethylformamide-phosphorus oxy chloride, 46, 20 from alky 1 halides, 47, 97 from oxidation of alcohols with dimethyl sulfoxide, dicyclohexyl carbodumide, and pyndimum tnfluoroacetate, 47, 27 Alkylation, of 2 carbomethoxycyclo pentanone with benzyl chloride 45,7... 

The iji vitro experiments, using the S-9 fraction from livers of uninduced Fisher 344 rats, was complicated by the fact that it became apparent that formaldehyde production was a poor measure of the extent of metabolism. The reason for that was that the S-9 fraction apparently catalyzed the oxidation of formaldehyde to formate. Consequently, determination of formaldehyde in an S-9 catalyzed reaction consistently gave low values of nitrosamine metabolism. Many workers use semicarbazide to suppress formaldehyde loss. We found, however, that semicarbazide is not a neutral bystander. 

The anodic oxidation of a number of 1-arylmethylenesemicarbazides (60) has been studied in CH3CN-AcOH containing sulfuric acid.118 This method provides a convenient preparative route to either oxadiazole (61) or triazoli-none (62) derivatives. The reactions were very sensitive to the concentration of water and under ordinary conditions the oxadiazole (61) is formed in 85% yield by oxidation of l-(p-methoxybenzylidene)semicarbazide. By addition of acetic anhydride, in order to reduce the water content, the triazolinone derivative 62 was formed in 45% yield [Eq. (50)]. 

Semisynthetic enzymatic oxidation of peptide alcohols employs equine liver alcohol dehydrogenase. Amino alcohols with nonpolar side chains and Z-Om[CH2OH] worked as effective substrates while polar amino alcohols such as H-Arg[CH2OH] and H-Lys[CH2OH] failed as substrates. To attain complete oxidation, semicarbazide was present in the reaction mixture to immediately trap the aldehyde, and flavin mononucleotide was used to oxidize the NADH to NAD+, which serves to oxidize the alcohol 41] Configurational stability was confirmed by NMR spectroscopy as in the case of Ac-Phe[CH2OH], which was prepared by sodium borohydride reduction of Ac-Phe-H 4 1... 

This general approach to the 1,2,3,5-thiatriazole ring was also used to prepare l,2,3,5-thiatriazolidine-4-one-l-oxides 36 (X = 0) and 1,2,3,5-thiatriazolidinc l-thione-l-oxides 36 (X = S) by the reaction of semicarbazides 35 (X = O) and thiosemicarbazides 35 (X = S), respectively, with thionyl chloride in methylene chloride solution (Equation 10) <1979JHC895>. 

A profound understanding of the reaction mechanism through which H202 is being formed could obviously enable optimization and lead to a maximal efficiency of such photochemical systems. Laser flash photolysis was thus employed to study the primary and secondary photochemical reactions in which lumiflavin and Ru (Il)-tris (2, 2 -bipyridine) are involved. Fig. 2 shows that photoexcited lumiflavin in its triplet state (picture a) is efficiently quenched by semicarbazide (picture c) this leads to flavosem iquinone formation (picture b). Further addition of molecular oxygen allows oxidation of flavosemiquinone radicals (picture d). On the other hand, Fig. 3 shows that photoexcited Ru (Il)-tris (2, 2 -bipyridine) is efficiently quenched by... 

Cyclization in phosphorus oxychloride of semicarbazides (79 X = NHR) yields aminooxadiazoles (81) whereas thermolysis leads to loss of ammonia (when X = NH2) and formation of an oxadiazolinone (80). Cyclization to aminooxadiazoles (81) occurs when thiosemicarbazides (82) are heated with an oxidizing agent such as lead oxide. This reaction has been widely applied to the synthesis of aminooxadiazoles, sometimes in low yields, and has been used to prepare 2-amino-l,3,4-oxadiazole (81 R1 =R2 = H). 5-Methyl ethers of thiosemicarbazides (82) cyclize, with loss of methanethiol, to aminooxadiazoles (81) on heating, but in PPA cyclization to 2-methylthio-l,3,4-oxadiazoles occurs. 

Synthesis of nitrobenzoxazolones-2 by Beckman s rearrangement of 4-nitrosalicylhy-droxamine add has been reported [509], The process is carried out on heating (4-nitro-2-oxyphenyl)-urea [510] or 4-(4-nitro-2-oxyphenyl)semicarbazide [511] with mineral acids and by oxidation of 6-nitro-2-hydroxymethylquinoline and its derivatives. 

Triazolo-diazocine 12 was obtained through a [6+2] cycloaddition of cycloocta-l,3-dione and 4-pyren-l-yl-l,2,4-triazole-3,5-dione 80. Such a triazole derivative was obtained by in situ oxidation of l,2,4-triazolidine-3,5-dione 81, which was in turn obtained by reacting isocyanates and semicarbazides, followed by base-catalyzed cyclization... 

The carbonyl group is a reactive function and, although aromatic aldehydes are somewhat less reactive than their aliphatic counterparts, benzaldehydes have an extensive chemistry. Many reactions replicate those of aliphatic aldehydes, but are mentioned here for completeness. Thus, oxidation of the carbonyl group leads to carboxylic acids and reduction gives alcohols. The aldehyde group reacts with a range of N-nucleophiles (Scheme 6.9). Imines (Schiff bases) are formed with amines and hydrazones with hydrazines. Semicarbazide gives semicarbazones and hydroxylamine forms oximes. 

Arylhydrazines undergo complex oxidation reactions from which a variety of products such as arylhydrocarbons, biarj ls, azo compounds, tetrazenes and phenols may be obtained. Hypochlorite oxidation of aryl semicarbazides, however, affords aryl azides possibly by... 

In this way, alkoxides, glycolates, catecholates, carboxylates, or Schiff base complexes have been obtained.37,38 Other metal chelates have been synthesized by electro-oxidation of the bare metal electrode phosphido, azolates, phthalocyanines, semicarbazides, Schiff bases, etc.37 In addition to the syntheses of monometallic complexes, electrochemistry has been proven to yield polynuclear complexes by using assembling or multidentate ligands.37... 

The periodate oxidation of 165 and its derivatives gave 195, which could be transformed into a variety of derivatives (194 and 196) (80MI8) upon reaction with amines, hydrazines, semicarbazide, or thiosemicarbazide (Scheme 44). The thiosemicarbazones 196 were cyclized to the thiadiazoles 199 and thiadiazolines 198, which are of chemotherapeutic interest (80MI8). The aldehyde also affords the expected dimedone derivative 197. 

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