Diazonium salts, coupling with

Aminothiazoles and their Derivatives C. Coupling with Diazonium Salts... 

Aminothiazole (58, 235, 391) and 2-amino-4-alkylthiazoles (391. 399) couple with diazonium salts. This reaction takes place in the 5-position and is possible even when bulky substituents occupy the 4-position. as exemplified by the reaction of 191 (Scheme 121) (400. 401). Me... 

Other typical electrophilic aromatic substitution reactions—nitration (second entr-y), sul-fonation (fourth entry), and Friedel-Crafts alkylation and acylation (fifth and sixth entries)—take place readily and are synthetically useful. Phenols also undergo electrophilic substitution reactions that are limited to only the most active aromatic compounds these include nitrosation (third entry) and coupling with diazonium salts (seventh entry). 

With the synthesis of the benzylidene hydrazones of selenazoles, it was possible to prepare formazans containing a selenazole ring. Of the compounds already described (Section I,C,1), 2-benzylidene-hydrazino-4,5-diphenyl- and 2-benzylidenehydrazino-4-methyl-5-carb-ethoxy-selenazole were used to couple with diazonium salts in order... 

If a C—H bond is acidic enough, it couples with diazonium salts in the presence of a... 

It has long been recognized that carbazole couples with diazonium salts just once, at C-3, to give monoarylazo products.9-Alkylcarbazoles react comparably. The use of sodium 4-dodecylbenzene sulfonate as a phase transfer catalyst was unsuccessful in an attempt to induce diazocoupling in both rings of 9-ethylcarbazole. 3,6-Dihydroxy-9-methylcarbazole likewise coupled only once, at C-2, with variously substituted benzene diazonium cations, whereas 3,6-dihydroxycarbazole itself coupled twice at 2- and 7-positions with a-naphthyldiazonium ion. ... 

Salicylic acid couples with diazonium salts in the expected manner. With diazotized aniline, ie, benzenediazonium chloride, the primary product is 5-phenylazosalicylic acid [3147-53-3] (eq. 7). 

Benzodiazepines do not show the high reactivity to electrophilic substitution exhibted by (204) but they can be brominated and coupled with diazonium salts at the 3-position. Treatment with sodamide and methyl iodide gives the 3-methyl derivative and by similar means the diazepinone (170) can be alkylated at the 5-position. 

In the case of active methinyl compounds, which, of course, lack the necessary mobile hydrogen, coupling with diazonium salts results in azo compounds. 

Since A,A -disubstituted hydrazines are readily available from a variety of sources (see Volume I, Chapter 14), their dehydrogenation constitutes a widely applicable route to both aliphatic and aromatic azo compounds. Such oxidative procedures are of particular value in the aliphatic series because so many of the procedures applicable to aromatic compounds, such as the coupling with diazonium salts, have no counterpart. The oxidation reactions permit the formation not only of azoalkanes, but also of a host of azo compounds containing other functional groups, e.g., a-carbonyl azo compounds [83], a-nitrile azo compounds [84], azo derivatives of phosphoric acid [85], phenyl-phosphoric acid derivatives [86],... 

The primary aromatic amines which will be preferentially nitrosated rather than diazotized are those which do not bear strongly electron-withdrawing substituents and are capable of coupling with diazonium salts to give azo dyes. 

If a C—H bond is acidic enough, it couples with diazonium salts in the presence of a base, most often aqueous sodium acetate.153 The reaction is commonly carried out on compounds of the form Z—CH2—Z, where Z and Z are as defined on p. 464, e.g., P-keto esters, p-keto amides, malonic ester. 

Quinolone (122), 2-pyridone (123), kojic acid (124) and 4-hydroxycoumarin (125) couple with diazonium salts (to form azo compounds, e.g. 126) and undergo Mannich reactions (e.g. with HCHO + HNMe2 to form -CH2NMe2 derivatives) at the positions indicated. Chromones undergo the Mannich reaction to give, for example, (127). 

Other classical synthetic approaches to 2-furanamine have failed, including the Curtius method and Beckmann rearrangement of 2-benzoylfuran oxime. However, hydrazinolysis of AT-(2-furyl)phthalimide, obtained from phthalimide and 2,5-dimethoxy-2,5-dihy-drofuran, gives 2-furanamine which was not isolated but detected by GLC-MS and H NMR spectroscopy. The latter reveals the absence of imino tautomers (75AP713). The chemistry of 2-dialkylamino-5-phenylfurans is typical of enamines protonation occurs on carbon to produce iminium salts. They are stable to base but afford 5-phenylfuran-2(3//)-one on hydrolysis with dilute acid. 2-Morpholino-5-phenylfuran couples with diazonium salts and affords Diels-Alder adducts with maleic anhydride and IV-phenylmaleimide (73JCS(P1)2523). 

Exercise 26-16 Reduction of 9,10-anthracenedione with tin and hydrochloric acid in ethanoic acid produces a solid, pale-yellow ketone (mp 156°), which has the formula C14H10O. This ketone is not soluble in cold alkali but does dissolve when heated with alkali. Acidification of cooled alkaline solutions of the ketone precipitates a brown-yellow isomer of the ketone (mp 120°), which gives a color with ferric chloride, couples with diazonium salts (Section 23-1OC), reacts with bromine, and slowly reverts to the isomeric ketone. 

Coupling Components With Condensed Cyclic Ammo nium Residues. Heterocyclic compounds in which the condensed benzene ring is substituted by a hydroxyl or an amino group can be coupled with diazonium compounds and may also be quatemized, either prior or subsequent to the coupling reaction, to yield cationic azo dyes. l,2-Dialkyl-6-nitroindazolium salts are reduced to the 6-amino compounds and then coupled with diazonium salts of aromatic amines. These dyes (e g., 21) color polyacrylonitrile in bright yellow to orange shades [64],... 

A-Coupling with diazonium salts occurs fairly readily in phenan-thridium salts bearing an amino group at C-8. Many diazoamino compounds have been so prepared in the search for trypanocides,344-348... 

Pyrazole itself does not couple with diazonium salts under normal conditions, but the presence of electron-donating groups facilitates this reaction. Thus, 3- and 5-hydroxypyrazoles readily couple in the 4-position (for example see Rosengarten134 and Knorr813), and 4-hydroxypyrazole in position 5.598 Azo coupling occurs analogously in the 4-position of 5-aminopyrazoles.598,599,614,615... 

As already mentioned, hydroxypyrazines exist in tautomeric equilibria with the corresponding pyrazinones which are normally the predominant species in the equilibria. Some of the reactions of hydroxypyrazines are reminiscent of those of phenols they can, for example, be coupled with diazonium salts and brominated and nitrated in either the ortho or para position to the hydroxyl group. Coupling with diazonium salts occurs in neutral or weakly alkaline solution, but if the reaction is carried out in 1 M sodium hydroxide solution, arylation of the pyrazine ring takes place. From hydroxy-pyrazine and benzenediazonium chloride 47% 2-hydroxy-3-phenyl-and 4% 2-hydroxy-3,6-diphenylpyrazine are obtained. 

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