Diazo groups

The diazonium salts usually decompose when warmed with water to give a phenol and nitrogen. When treated with CuCl, CuBr, KI, the diazo group is replaced by chlorine, bromine or iodine respectively (Sandmeyer reaction). A diazonium sulphate and hydroxyl-amine give an azoimide. The diazonium salt of anthranilic acid (2-aminobenzoic acid) decomposes to give benzyne. ... 

When a solution of a diazonium salt is heated, the diazo group is replaced by hydroxyl and nitrogen is evolved ... 

Diazo compoimds are partieularly easy to make with the diazo group next to a carbonyl group by this reaction ... 

As final examples, the intramolecular cyclopropane formation from cycloolefins with diazo groups (S.D. Burke, 1979), intramolecular cyclobutane formation by photochemical cycloaddition (p. 78, 297f., section 4.9), and intramolecular Diels-Alder reactions (p. 153f, 335ff.) are mentioned. The application of these three cycloaddition reactions has led to an enormous variety of exotic polycycles (E.J. Corey, 1967A). 

Diazoindazole (51) is one of the few heterocyclic diazo compounds whose structure has been determined (78AX(B)293). The diazo group shows a substantial carbanionic character (51b). 

A Hammett relationship of the form ApK = 5.8am has been proposed for 4-substituted pyrazoles (74TL1609) in order to explain the effect of 4-nitro ApK = 4.5, am = 0.71) and 4-diazo groups (Apiifa = 10.0, am = 1.76). The acidity constants of a series of pyrazolidine-3,5-diones have been determined (75AJC1583) and the 4- -butyl-1,2-diphenyl derivative phenylbutazone has a pK of 4.33. 

Iminopenicillanic acid derivatives have been particularly useful in the preparation of 6a-methoxypenicillanates (note that the 6-diazo group is a special case of the 6-imino function, and that a 6-acyliminopenicillanate was obtained from the 6-keto derivative in Scheme 37). 

S. Patai, ed.. The Chemistry of Diazonium and Diazo Groups, John Wiley Sons, New York, 1978. 

The addition of diazo compounds generally leads to three membered tings, although in special cases, linear adducts with an intact diazo group [110] or l,3,4-oxadiazol-3-ines [111] can be isolated Most diazo compounds are unstable and yield oxirans and aziridines [112,113,114] Aziridines are obtained exclusively on reaction of certain polyfluorinated acyl imines with diazomethane [115]... 

B (11— 12— 14). Examination of a more recent study suggests the von Richter reaction probably involves simultaneous attack of the triple bond on the diazo group accompanied by attack by a halide ion but not by a water molecule. The halocinnoline 13 is then hydrolyzed under the von Richter reaction conditions to furnish the 4-hydroxycinnoline derivative 14 (11 - 12- 13 14, pathway A). 

In general, it is diffieult to prediet the outeome of eyelizations of alkynylpyrazole diazonium salts, even with elosely related arrangements of funetional groups, sinee reaetion ean oeeur at both the a- and /3-earbon atoms of the aeetylenie substituent. Moreover, it is known that the eleetrophilieity of the diazo group and the nueleophilieity of a triple bond markedly depend on their positions in the pyrazole ring and that this ean affeet both the eourse and ease of eyelization and even its viability (83IZV688). 

Methyl-1,2,4-benzotriazm-3(4//)-one 1-oxide 122 can be obtained in good yield by the diazotization of 121 to give 3-diazo-7-methyl-l,2,4-benzotriazine 1-oxide followed by the substitution of the diazo group with water (82JHC497). 

Itishould be noticed that the similarity between the osmophore theory and Witt s chromophore colour theory does not extand much beyond the initial conception and there seems to be no connection between the odour and the colour of a body, it is indeed quite the exception for a body to have both a strong odour and a strong colour. Two prolific sources of colour, viz. the diazo group and a large molecule have no counterpart as regards odour, and it is probably only by chance that quinone and chroman both have pronounced odours and are the sources of colour. 

The most comprehensive modern works on the subject are the relevant volumes of Patai s series The Chemistry of Functional Groups, namely the two volumes on diazonium and diazo groups (Patai, 1978), the two volumes on hydrazo, azo, and azoxy groups (Patai, 1975) and the two Supplement C volumes on triple-bonded groups (Patai and Rappoport, 1983). Supplement C contains chapters on arene- and alkene-diazonium ions and on dediazoniation reactions. 

This diazotization is typical of many aminoazoles the diazonium ions formed are relatively strong acids. The pATa values of five di-, tri-, and tetrazolediazonium ions are reported to be between 3 and 4, i. e., about 10 units lower (more acidic) than those of the respective unsubstituted heterocycles (Vilarrasa et al., 1974). Therefore, deprotonation of the diazonium ion is easy and, depending on reaction conditions, yields either the diazonium salt or its conjugate base, the diazo compound. The electrophilic reactivity of the P nitrogen atom in the diazo group of the base is lower than the reactivity of the diazonio group of the cation (Diener and Zollinger, 1986 see Sec. 12.2). 

Quinone diazides can also be obtained by the diazo group transfer reaction of 4-tosyl azide. For example, 9-diazo-10-anthrone (2.55) is formed from anthrone (2.54) if the reaction is carried out in an ethanol-piperidine mixture. On the other hand, if ethanol is replaced by pyridine, dimerization with loss of molecular nitrogen takes place and the azine 2.56 is isolated (Scheme 2-32 Regitz, 1964 Cauquis et al., 1965). In the preceding discussion tosyl azide was shown to be an electrophilic reagent. It therefore seems likely that it is not the anthrone 2.54 but its conjugate base which reacts with tosyl azide. 

A diazo group can be introduced adjacent to a single carbonyl group indirectly by first converting the ketone to an a-formyl ketone (10-118), and then treating it with tosyl azide. As in the similar cases of 12-7 and 12-8, the formyl group is cleaved... 

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