Phenylhydrazones oxidation

A number of years ago it was observed that the perbenzoic acid oxidation of benzaldehyde phenylhydrazone afforded a high-melting product of low solubility which was termed benzaldehyde phenylhydrazone oxide. More recent work has shown that this, as well as related oxidation products of other phenylhydrazones, is, in fact, the cis isomer of the corresponding azoxy compounds [4, 7]. 

Usually prepared by the action of NaCN on benzaldehyde in dilute alcohol. It is oxidized by nitric acid to benzil, and reduced by sodium amalgam to hydrobenzoin PhCHOHCHOHPh by tin amalgam and hydrochloric acid to des-oxybenzoin, PhCH2COPh and by zinc amalgam to stilbene PhCH = CHPh. It gives an oxime, phenylhydrazone and ethanoyl derivative. The a-oxime is used under the name cupron for the estimation of copper and molybdenum. 

Papaverinic acid, CieHjjO N. HjO, crystallises in small tablets, m.p. 233°. It is dibasic, readily forms an anhydride, furnishes an oxime and a phenylhydrazone, contains two methoxyl groups, and on oxidation yields veratric and pyridine-2 3 4-tricarboxylic acids, and hence is represented by the following formula —... 

Another example of this rearrangement has been used to prepare 1,2,3-triazole 146 from furazanic phenylhydrazone 147 (Scheme 84) [93JCS(P1)2491]. Interestingly, furoxanic Z-phenylhydrazones 150 underwent thermal recyclization to 1,2,3-triazole A-oxides 152, evidently through intermediate 151. Treatment of the hydrazone 150 with rerr-BuOK leads to the nitromethyl derivative 149 [OOOMIl] (Scheme 84). Lead tetraacetate oxidation of 147 with subsequent Lewis acid treatment of the initially formed intermediate afforded indazole 148 (Scheme 84) (85JHC29). 

Dichloroethylphosphine has been shown to react with methyl vinyl ketone to form 2-ethyl-5-methyl-A -l,2-oxaphospholen-2-oxide (25), which has been converted to (26) by chlorination in the presence of base. The same phosphine adds to methyl acrylate in the presence of acetic acid to give the phosphine oxide (27). Further examples have appeared of the reactions of the phenylhydrazones of methyl ketones with phosphorus trichloride to produce the heterocycles (28). 

It was observed in those cases in which the oxidation was arrested too soon that an appreciable amount of silver chloride was deposited when the solution was concentrated. Furthermore, the mother liquor, when treated with phenyl-hydrazine in acetic acid, deposited some yellow crystalline D,L-mannose phenylhydrazone, m. p. 195-200° (Maquenne block). It is apparent that too vigorous oxidation results in the formation of hexoses. 

A strategy has been described for the synthesis of 2-ethyIthio-6-(3-hydroxy-1,2-0-isopropylidenepropyl)pteridin-4(3//)-one 90 which can be used as a useful intermediate for the conversion of neopterin to biopterin. Diaminopyrimidinone 86 reacts with D-arabinose phenylhydrazone 87, the obtained diastereomeric mixture 88 is converted into its isopropylidene derivative 89 which under oxidation conditions yields 90 <00H(53)1551>. 

Both L-gulose12,13 (9) and D-gulose (d-9, see Ref. 10) have been oxidized with bromine to L- or D-gulonic acid, respectively (see Scheme 1). L-Gulose (9) has been prepared by a number of different procedures. Schemes 2 and 3 show two early procedures that afforded L-gu-lose, but the overall yields were low (<30%). In the first procedure12 (see Scheme 2), D-glucitol (10) was converted into 2,4-O-benzylidene-D-glucitol (11), which was then oxidized with lead tetraacetate to 2,4-O-benzylidene-L-xylose (12). Nitromethane was added to 12 to afford crystalline 13 in 50% yield. Hydrolysis of 13 provided 14, which was treated with sodium hydroxide, followed by sulfuric acid, to afford 9, which was isolated in 52% yield as the 2-benzyl-2-phenylhydrazone. 

The oxidation of A -phenylhydrazones in the presence of pyridine leads to the formation of 5-triazolo[4,3a]pyridinium salts hy attack of pyridine as a nucleophile on the nitrilimine intermediate (Scheme 54) [77]. 

Anodic oxidation of formazane 18 [17], 1-arylmethylenesemicarbazide 19 [55], p-nitrobenzaldehyde phenylhydrazone 20 [56], and 2-benzoylpyridine phenylhydrazone 21 [57] afforded the corresponding heterocycles in a very good yield (Scheme 14). The homogeneous oxidation of compounds 18-20 was carried out by indirect electrolysis by the mediators generated in situ [58]. 

Anodic oxidation of the monooxime phenylhydrazone of a 1,2-dicarbonyl compound 93 in CH3CN-O.I mol/I Et4NC104 solution gave 2-phenyl-1,2,3-triazol-1-oxide 94 in very good yield [125,126] (Scheme 51). 

Phenylhydrazones were oxidized by NiOa at 0 °C via a radical mechanism to afford C-C and C-N dimers. ... 

Many oxidizing agents have been used, especially copper sulfate and other cupric salts. Potassium dichromate in acetic acid and manganese dioxide are good oxidants for benzil bis(phenylhydrazone). Nitrous acid has been used for the osazones of acetylated sugars and for phenylglyoxal bis(phenylhydrazone). ... 

The phenylhydrazone of A(-acetylisopelletierine (iV-acetyl-2-piperidylace-tone) was hydrogenolyzed over platinum oxide in acetic acid at 25 and 3 atm to l-(iV-acetyl-2-piperidyl)-2-aminopropane in 92% yield [952], and the... 

The condensation of 2,4,5-triamino-6-hydroxypyrimidine and 5-deoxy-L-arabinose phenylhydrazone 1042, followed by oxidation of the intermediate 1043, gave biopterin 1044. The tetrahydrobiopterin is the natural cofactor of phenylalanine hydrolase. Various stereochemical isomers were also pre-... 

Oxidation of ketone phenylhydrazones generates a radical-cation centre on the nitrogen atom adjacent to the benzene ring. The radical-cation is delocalised by both the hydrazone group and the phenyl ring. Reactions of 1,3,5-triphenyl-A -pyazolines illustrate the properties of these radical-cations. Two one-electron waves are seen at a rotating disc electrode in acetonitrile and for 1,3.5-triphenyl-pyrazoline, Ey. = 0.82 and 1.68 V vs. see [33]. The delocalised radical-cation is... 

Open chain ketone phenylhydrazones take part in a number of cyclization reactions to form heterocyclic rings. Many of the electrochemical reactions describe can also be achieved using chemical oxidising agents. In general, electrochemical oxidation proceeds to the two-electron level to generate an electrophilic species... 

Oxidation of chalcone phenylhydrazone 13 leads to a pyrazole and the expelled proton catalyses formation of a pyrazoline from the chalcone phenyl-hydrazone [43]. The latter undergoes further anodic oxidation (p. 308). In the presence of pyridine as a proton acceptor, the pyrazole becomes the major product. A further example of oxidative cyclization is the conversion of a-oximino phenylhydrazones to 1,2,3-triazole-l-oxides 14 [44]. 

Murakami et al. reported (575) a total synthesis of murrayaquinone A (107) by oxidation of l-hydroxy-3-methylcarbazole (23) with Fremy s salt, as previously described by Martin and Moody (632). The hydroxycarbazole 23 required for this synthesis was obtained via the Fischer indolization of the O-methanesulfonyl phenylhydrazone 614 (575) (see Scheme 5.38). The oxidation of l-hydroxy-3-methylcarbazole (23) with Fremy s salt afforded murrayaquinone A (107) as the major product, along with a 5% yield of isomeric carbazole-l,2-quinone 876 (575) (Scheme 5.108). 

Hajipour and coworkers prepared benzyltriphenylphosphonium peroxymonosulfate (BnPhsPHSOs) in a very high yield (95%) and purity (99%). This new oxidizing reagent was applied successfully in various deprotection reactions such as the conversion of oximes, phenylhydrazones, 2,4-dinitrophenylhydrazones and semicarbazones to the corresponding carbonyl compounds in the presence of bismuth chloride under nonaqueous conditions . Oxidative deprotection of trimethylsilyl ethers, tetrahydropyranyl ethers and ethylene acetals with BnPh3PHS05 under microwave irradiation affords the corresponding carbonyl compounds in very high yields (equation 71). The same reaction also proceeds under nonaqueous conditions ". 

Phenylazo-alkane lagern sich unter dem EinfluB von Radikalbildnem (z. B. Dibenzoylper-oxid), Basen (z. B. Natriummethanolat), Sauren (z. B. Schwefelsaure), Alkalien oder hohen Temperaturen in die entsprechenden Phenylhydrazone urn, wahrend die entgegengesetzte Umlagerung nicht gelingt1 ... 

Die Oxidation von Hydrazonen mit organischen Persauren fiihrt in einigen Fallen zur Bildung von Azoxy-Verbindungen zur Umsetzung von Benzaldehyd-phenylhydrazon mit Persauren s. ds. Hdb., Bd. X/3, S. 475. 

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