Aryl—Azo

In a basic medium, 5-nitro-5-hydroxymethyltetrahydro-l,3-oxazine derivatives can be coupled with aryl diazonium salts to form aryl-azo derivatives (54) with the elimination of a molecule of formaldehyde. ... 

Perfluoroalkyl carbanions, generated by reversible nucleophilic addition of a fluoride anion to fluoroalkenes, react with dry benzenediazonium chloride in dimethyl formamide, giving phenylazoperfluoroalkanes in 41-53% yield (Dyatkin et al., 1972). The dianion obtained from 1,2-dinitrobenzene with dipotassium cyclo-octatetraenide reacts in a complex way with arenediazonium salts, forming 4-aryl-azo-2-nitrophenol in 46-58% yield (Todres et al., 1988). 

Ester and cyano groups generally resist substitution by aryl azo groups and must first be hydrolyzed to produce carboxyl and carbonamide groups respectively, which can be more easily eliminated [62], Unsymmetrical formazans can be produced according to Scheme 2.15. 

The single crystal X-ray structure of fra .y-[Ru(bipy)2(PPh3)2]2+1122,1123 and the synthesis of related bis(phosphine) complexes1005 have been reported. Reaction of [RuCljL ] (L = bipy,1124, 2-(aryl-azo)pyridine1066) with phosphine, arsine and stibine ligands (I/) affords the complexes [RuC1(L)2L ]+ while with bidentate ligands L [Ru(bipy)2L ]2+ can be isolated.1124 (See Section 45.5). 

An important reaction of aryl azo ligands is Cyclometal-lation by activation of the ortho C H proton and snbsequent C M coordination (eqnation 14). 

Arylazo-3-pyrazolin-5-ones have been used as dyes. They form complexes with chromium which have good dyeing properties.1060 Miehaelis, Kotelmann and Drews984 report the reduction of 4-aryl-azo-3-pyrazolin-5-ones having no 1-substituent to pyrazoles by use of phosphorus pentasulfide (eq. 202). Reaction of such azo compounds... 

For purposes of classification the 4-aminopyrazoles are considered to be 4-imino-2-pyrazolines and analogs of 2-pyrazolin-4-ones. These compounds are listed in Table XL. Such compounds can be prepared by direct cyclization using ethyl diazoacetate and ethyl cyanoacetate.92 This is the same as eq. 243, except that the malonic ester is replaced by ethyl cyanoacetate. Purines can be hydrolyzed to 4-imino-2-pyrazolines by using strong acid.1210 1846 By far the most frequently used preparation is reduction of appropriately substituted pyrazoles, such as 4-nitro,368,812,819,1015,1019,1049 4-nitroso1165 or 4-aryl-azo.671 974,995 The hydrolysis of the carbethoxy 4-imino-2-pyrazolines derived from ethyl cyanoacetate and ethyl diazoacetate forms 4-imino-2-pyrazolin-3-carboxylic acid which is readily decarboxylated to the parent compound.92... 

Aryl Azo Compounds. Alkyl- (including tert-butyl) and aryllithium reagents add to azo benzene to give trisubstituted hydrazines in fair to excellent yields (see Eqs. 44 and 45) alkylation of the intermediate anion in situ leads to tetra-substituted hydrazines.211 Benzyl and heteroarylmethyl (see Eq. 54) anions and the enolate of phenylacetamide add to azo benzene in fair to excellent yields.212 Aromatic Grignard reagents are reported to reduce azo benzene and its derivatives to the hydrazo compounds (cf. also Eq. 20).213 The only other aryl azo compound investigated in animations appears to be benzo[c]cinnoline.214... 

Although indoles are less reactive than pyrroles, they react with arenediazonium salts to give 3-(aryl-azo)indoles. The reaction with carbonyl compounds proceeds in an analogous way in the presence of acids. For this reason, indoles unsubstituted in the 3-position give a positive colour test with Ehrlich s reagent. Indole and acetaldehyde react via an azafulvenium salt to give 3-Vinylindole, which on further reaction with indole forms l,l-di(indol-3-yl)ethane ... 

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