Phenylazo derivatives

The reaction of amines with the 4-phenylazo derivative (228) results in their rearrangement into triazolines. Depending on the basicity of the amines and the size of the alkoxy group, three different triazolines (229. 230, and 231) are obtained (Scheme 117) (454. 459, 472). In all cases, the first step involves nucleophilic addition of the amine to the carbonyl group followed by ring opening and further ring closure. 

Bulka et al. (43) have demonstrated the electrophilic reactivity of selenazoles possessing an hydrazonc in the 2-position and nonsubstituted in the 5-position toward diazonium salt to give 5-phenylazo derivatives preferentially. For example, the main product of the coupling of 2-benzylidene hydrazino-4-phenylselenazole with diazo-o-phenetidine is the 5-(o-ethoxyphenylazo)-selenazole (Scheme 371 ruby red prisms, m.p. 206°C. yield 67"o). A formazan is obtained as by-product. (See Section III.6) (43). 

Heating 9-hydroxy-2-methyl-8-nitro-4//-pyrido[ 1,2-a]pyrimidin-4-one 326 in dimethylformamide in the presence of hydrazine hydrate and Raney nickel at 50°C afforded 8-amino derivative 327 (92KGS1660). 8-Amino derivative 327 was also prepared from 8-phenylazo derivative 328. 

Like its sulfur and selenium analogs, 2,6-diphenyl- 1,4-ditellurofulvene 2 on treatment with amyl nitrite and phenyldiazonium tetrafluoroborate undergoes electrophilic substitution at the terminal methine carbon, giving rise to the corresponding nitroso and phenylazo derivatives (81CC828). 

Triamino-2-thioxo-l,2-dihydro-l,8-naphthyridine-3-carbonitrile (15, R = H) underwent azo coupling with benzenediazonium chloride to give its 6-phenylazo derivative (15, R = N NPh) (NaOH, EtOH 86%).538... 

Strychnidine has not been halogenated or nitrated, but has been coupled with benzenediazonium chloride to give a 2-phenylazo derivative (44), reduced to 2-aminostrychnidine. Reduction of 2-nitrostrychnine gives 2-aminostrychnine (42). 

Aryldiazonium salts also react with cyclopentadienylides to give 2- or 3-phenylazo-derivatives . ... 

In another instance, when the dialdehyde 125 is treated with phenylhydrazine, a cyclization occurs, probably via the monophenylhydrazone 126 to give the phenylazo derivative 127,... 

When an amino group is in a peri position with respect to the heteroatom [as in (54 after reduction)], an imidazole ring may be built to join the two by reaction with a carboxylic acid and PPE [2SI3]. Replacing the carboxylic acid by urea in the cyclization of (54.5) leads to the formation of a doubly fused imidazol-2-one ring [2513]. An imidazol-4-one may be constructed by the reaction of cither phenylglyoxal [3039, 3188] or the phenylazo derivative of chloroacetyl chloride [2366] with a 2-aminoazine. 

N. Thankarajan and K. M. Nair, Metal chelates of phenylazo derivatives of (S-dicarbonyl compounds, J. Indian Chem. Soc., 53 (1976) 1156-1157. 

If the mixture of cyclopentadienyllithium and the phenylazo derivative (Li-C5H5-N = N-Ph) reacts with ferrous chloride, ferrocene and the ferrocene phe-nyldiazo derivative ( / -C5H5)Fe(// -C5H5-N = N-Ph, 18%) is produced [11,12]. 

Fig. L Mechanism of the azo coupling reaction of bilirubin. If coupling is performed with 2 mole proportions of diazotized aniline bilirubin is cleaved at the central methylene bridge to yield a mixture of isomers composed of equimolar amounts of the phenylazo derivatives of vinyl- and isovinyineoxanthobilirubinic acid. The reaction proceeds in two steps these are shown in A and B, respectively.

Fig. 3. Diagrammatic representation of the fractionation procedure used for the isolation of the phenylazo derivatives of bile bilirubin. For details, see Section III, B. (Reproduced by courtesy of the Biochemical Jourtuil.)...

The overall procedure employed by the author (Kuende, 1970a) to isolate the phenylazo derivatives of the bile bilirubin is shown diagrammati-cally in Fig. 3. Human hepatic bile served as the source of bilirubin conjugates. A total of 15.3 liters of bile was processed in this investigation. The bile was sampled postoperatively from cholecystectomized patients through a T tube. Bile specimens from several patients were pooled, and were kept frozen until processed further. The isolation was carried out in three steps. Gare was taken to apply the mildest of conditions at all stages. 

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