Chemistry diazotization

Diazonium salts of thiazoles are among the most widely used intermediates in thiazole chemistry. They are prepared by diazotization of... 

Peter Griess synthesized the first azo dye soon after his discovery of the diazotization reaction in 1858. The two reactions which form the basis for azo dye chemistry are diazotization (eq. 1) and coupling (eq. 2) (2). 

Another total synthesis used the rich chemistry of iminophosphoranes (95AHC159). The /3-(3-indolyl)vinyl iminophosphorane 354 underwent an aza-Wittig/electrocyclic ring closure reaction to give the carboline 355 which was hydrolyzed with lithium hydroxide (Scheme 106). A selective reduction, deprotection, decarboxylation and diazotation followed by ring closure gave Fascaplysine (353) (94TL8851). 

Among examples of the use of this method of internuclear cycliza-tion in heterocyclic chemistry is the conversion of diazotized amino-laudanosine (14) to 2,3,5,6-tetramethoxyaporphine (15), Eq, (23). ... 

In aromatic compds, an amino group may be replaced by the nitro group by diazotization and reaction with nitric acid in the presence of cuprous salts (the Sandmeyer reaction). This method is used for lab work only and is described in standard textbooks on preparative organic chemistry... 

A widely significant and crucial investigation of the mechanism of diazotization was made in 1899 by Hantzsch and Schumann widely significant because it was one of the first mechanistic investigations using appropriate methods of organic chemistry - extremely crucial because it influenced all subsequent investigations in the field of diazotization mechanisms until 1958. 

For reviews of rearrangements arising from diazotization of aliphatic amines, see, in Patai The Chemistry of the Amino Group Wiley NY, 1968, the articles by White, E.H. ... 

Our task was to develop a feasible synthesis for diamino resorcinol. From several possibilities [1-4] the resorcinol and anihne were chosen as starting materials. The diazotated aniline was coupled with resorcinol among basic conditions giving 4,6-bisphenylazo resorcinol. Hydrogenation of the latter resulted in diamino resorcinol and aniline, which could be recycled (scheme 14.2). This chemistry is well known [5-13] therefore, the research work focused on finding the optimal parameters and catalyst and finally on elaborating a process for scale-up. 

There is little or no well-defined chemistry of 2-amino-pyrones, -pyrylium salts, etc., because of the ease with which these systems undergo ANRORC reactions to give substituted pyridones (equation 88). 4-Aminopyrylium salts are reversibly deprotonated to the imines (equation 89). Amino groups in the 3- and 5-positions of pyrones can be diazotized normally. 

This diazotization reaction is compatible with the presence of a wide variety of substituents on the benzene ring. Arenediazonium salts are extremely important in synthetic chemistry, because the diazonio group (N=N) can be replaced by a nucleophile in a radical substitution reaction, e.g. preparation of phenol, chlorobenzene and bromobenzene. Under proper conditions, arenediazonium salts react with certain aromatic compounds to yield products of the general formula Ar-N=N-Ar, called azo compounds. In this coupling reaction, the nitrogen of the diazonium group is retained in the product. 

Ridd [5] and Kalatzis and Ridd [6] have written an interesting series of studies and reviews on the interrelationship of nitrosation, diazotization, and deamination. Other reviews covering various aspects of iV-nitroso chemistry are by Leotte [7], Overberger et al. [8], Dusenberg and Powell [9], Lashkarev and Vasyunas [10], Mannschreck et al. [11], Rademachereta/. [12]. Chapter 16 should also be reviewed for background material on nitrosations. 

There is considerable interest in the chemistry of triazines as some of these compounds show pronounced antimalarial, antimicrobial and antiviral activity (76JCS(Pl)252l). Therefore two types of thiophenes annelated with a triazine ring will be mentioned. Thieno[2,3-d]-1,2,3-triazines were synthesized by cyclization of diazotized 2-aminothiophene-3-carboxamides (equation 55) (73M1586). Treatment of 3-alkylthio-6-styryl-5-oxo-2,5-dihydro-l,2,4-triazines with phosphorus pentasulfide in pyridine yields thieno[2,3-e]-l,2,4-triazines (equation 56) (78CI(L)585). Probably a thiation with subsequent cycloaddition and elimination of a hydride ion is involved. 

In contrast to nitrosyls, the absence of a transferable oxygen atom in N2R ligands allows the preparation of stable diazenido complexes of oxophilic, early transition metals see for example Cp2TiCl(N2Ph). Furthermore, there are as yet no diazotate (RN=NO-) forming reactions anolo-gous to the nitrite forming reactions in nitrosyl chemistry (see equations 112 and 113). 

Diazodinitrophenol (DDNP, Dinol) 4,6-Dinitrobenzene-2-diazo-l-oxide, or diazodinitrophenol as it is more commonly called, occupies a place of some importance in the history of chemistry, for its discovery by Griess56 led him to undertake his classic researches on the diazonium compounds and the diazo reaction. He prepared it by passing nitrous gas into an alcoholic solution of picramic acid, but it is more conveniently prepared by carrying out the diazotization in aqueous solution with sodium nitrite and hydrochloric acid. 

Aromatic fluorination chemistry has a remarkably long history, and the first successful synthesis of aryl C-F bonds was reported in 1870 [22], Significant developments in the area in the early part of the 20th century included the discovery of Balz-Schiemann reaction [23,24] involving diazotization of an aromatic amine in the presence of tetrafluoroboric acid and the reaction scheme is shown in Fig. 4. The above reaction produces large quantities of waste (such as NaBF4,... 

The present, straightforward, two-step synthesis of 5.6-dimethoxyindazole from 3,5-dimethoxyacetophenone illustrates the usefulness of this amination reaction. With standard chemistry the introduction of a hydrazine group into the acetophenone molecule would have required four steps 1) nitration, 2) reduction of the nitro group to the aniline, 3) diazotization and 4) reduction of the diazonium compound to the hydrazine. 

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