Diazo nium salt

Nucleophilic processes that generate chloroindoles are largely confined to the displacements of oxy functions and Sandmeyer reactions of diazo-nium salts [81 H( 15)547]. A low yield of 2-chloroindole was obtained by a reaction sequence that involved treatment of oxindole with phosphoryl chloride, and then treatment of the Vilsmeier salt with sodium bicarbonate [66JOC2627 86H(24)2879]. It is, however, much better to prepare this compound from 2-lithioindole (92JOC2495). With phosphoryl chloride and dimethylformamide ethyl l-hydroxyindole-2-carboxylate failed to give the expected 3-formyl derivative. Instead there was a 50% yield of the 3-chloro derivative (84CPB3678). Diazonium salts have been used as precursors in... 

Fluorobenzimidazole has been made from the corresponding diazo-nium salt [75MI5 73JOC3647],... 

Careful observations of the course of iodo-de-diazoniation demonstrate that the detailed pathway of such reactions is still relatively complex. For instance, after adding a solution of KI to a solution of an arenediazonium salt, normally molecular iodine appears to be formed first, followed by a precipitate and evolution of N2. Carey and Millar (1960) isolated the salt ArNJIj- on adding iodide to the diazo-nium salt. Ion pairs (ArNjHlg-), suggested as primary products by Meyer et al. (1979), were identified for diazonium halides (Cl- and Br-) by Israel et al. (1983) as 1 1 complexes on the basis of JOB analyses of visible spectra (Benesi-Hildebrand method). Iodides were, however, not included in that investigation. 

Interaction of the Bi0Hi0(2—) anion with excess nitrous acid gives an inner diazo-nium salt (of unknown structure, possibly containing a nitronium ion) which is highly explosive in the dry state. It is readily reduced wet to the non-explosive l,10-bis(diazonio)decaboran(8)ate inner salt. 

A few diazoniiun salts are unstable in solution, and many are in the sohd state. Of these, the azides, chromates, nitrates, perchlorates (outstandingly), picrates, sulfides, triiodides and xanthates are noted as being explosive, and sensitive to friction, shock, heat and radiation. In view of their technical importance, diazo-nium salts are often isolated as their zinc chloride (or other) double salts, and although these are considerably more stable, some incidents involving explosive decomposition have been recorded. 

A mixture of 6 1. of water and 600 cc. of concentrated sulfuric acid is placed in a 12-I. round-bottom flask, and to it the diazo-nium salt solution is added all at once the resulting mixture is then heated (o boiling as rapidly as possible. The solution becomes turbid at first but gradually becomes clear after boiling for about forty minutes. The solution, which now contains a... 

Similarly, 1,3-diaryltriazenes ArNNNHAr, formed by condensation of ArNH2 with diazo-nium salts, behave as monodentate ligands in complexes cis- and trans-... 

Because of the special structural requirements of the resin-bound substrate, this type of cleavage reaction lacks general applicability. Some of the few examples that have been reported are listed in Table 3.19. Lactones have also been obtained by acid-catalyzed lactonization of resin-bound 4-hydroxy or 3-oxiranyl carboxylic acids [399]. Treatment of polystyrene-bound cyclic acetals with Jones reagent also leads to the release of lactones into solution (Entry 5, Table 3.19). Resin-bound benzylic aryl or alkyl carbonates have been converted into esters by treatment with acyl halides and Lewis acids (Entry 6, Table 3.19). Similarly, alcohols bound to insoluble supports as benzyl ethers can be cleaved from the support and simultaneously converted into esters by treatment with acyl halides [400]. Esters have also been prepared by treatment of carboxylic acids with an excess of polystyrene-bound triazenes here, diazo-nium salts are released into solution, which serve to O-alkylate the acid (Entry 7, Table 3.19). This strategy can also be used to prepare sulfonates [401]. 

However, isolation of the product or products formed by coupling with nitrobenzene and certain other compounds has been successful. From nitrobenzene and diazotized aniline (in the form of the stabilized diazo-nium salt), 4-nitrobiphenyl is obtained in 33% yield, and from o-nitro-... 

The thermal methods available for the formation of aryl cation in solution are limited to the solvolysis of suitable perfluorophenylalkyl esters and aromatic diazo-nium salts [6]. Furthermore, these methods lead to unselective chemistry due to the singlet nature of the aryl cation formed. Under photostimulation, and according to the substituents, aromatic halides give either the singlet or triplet phenyl cation. The mediation of triplet aryl cations is essential for achieving the chemoselectivity desired in these reactions [12]. In order to ensure the formation of such intermediates, certain conditions should be met ... 

An improvement of the previously reported Meerwein protocols was achieved by employing ionic liquids as chloride sources (Scheme 18) [93], Although this new version of the Meerwein reaction is still limited to activated alkenes such as acrylates, electron-donating as well as electron-withdrawing groups on the diazo-nium salt are tolerated. In earlier Meerwein arylations, a change in the substitution... 

To date, milder reaction conditions have only been reported with diazo-nium salts as coupling partners. These salts are typically more reactive than aryl iodides and have the extra advantage that no addition of base is generally required [73]. Different diazonium salts could be coupled with styrene derivatives and acrylates at room temperature (Table 2), even with catalyst loadings as low as 0.1 mol%. 

The furan ring undergoes arylation with diazo compounds, but the yield is poor. Thus, furfural,23 2-furoic acid,158 and furylacrylic acid can be converted into 5-substituted arylfuran derivatives by diazo-nium salts (see further references in Ref. 159) ... 

The most common "monovalent nitrogen groups which can be substituted by fluorine are the nitro (NO2). azido (N3), triazo (N = NNR2), and amino (NH2) groups. Replacement of the amino group is facilitated by transformation to either the corresponding activated diazo-nium salt (N2 by diazotization. or by quaternization to the ammonium salt (NRj" X ). 

The reaction of the amine with nitrous acid gives a diazo-nium salt and thence a carbocation. The product is formed by the 1,2-shift of a methyl group ... 

In the previous sections we have discussed reactions in which the carbon-azide bond is formed by substitution on carbon of a preformed azide moiety or by its addition to various multiple bonds. Processes in which the azide nitrogen atoms are introduced in a stepwise manner are now considered. These syntheses include the reactions of diazo-nium salts with nucleophiles such as ammonia, chloramine, hydroxyl-amine, hydrazine, sulphonamides and azide ion. Recent work on... 

The first examples reported by Sandmeyer date back to 1884. The many various preparative procedures differ mainly in the type and the preparation of the copper-cyanide complex which is used. In the Gattermann procedure KCN in the presence of Cu powder is used. Generally one tries to avoid the formation of HCN on the addition of alkali metal cyanide to the acidic medium by neutralizing the diazo-nium salt solution in advance with sodium or barium carbonate. Cyanogen, which is formed from CN ions on treatment with Cu" salts, is also a harmful by-product. In this case the addition of sodium hydrogen sulfite (equation 19) proved to be of great value. 

Derivation From m-chloraniline through the diazo-nium salt. 

Reactions that employ copper(I) salts as reagents for replacement of nitrogen in diazo-nium salts are called Sandmeyer reactions. The Sandmeyer reaction using copper(I) cyanide is a good method for the preparation of aromatic nitriles ... 

Unexpected products are sometimes obtained in the l horr reaction for example, during an attempt to synthesize an alkaloid, thermolysis of the diazo-nium salt (79.7) gave a triazinone, the carbonyl group probably arising from the oxidation of the methylene by nitrous acid. 

Zollinger and coworkers" " have also studied the diazo coupling reactions of diazo-nium salts extensively. The proposed mechanism for the N-coupling reaction between a diazonium ion and an aromatic amine involves formation of an amine-diazonium ion complex, 9, which is converted into a cr-complex, 10, which subsequently loses a proton to base forming the product (equation 43), where B is any base, i.e. the amine, the solvent or... 

Aminothiophene-2-carboxylic acid has been diazotized with isoamyl nitrite to form the diazo-nium salt which, on thermolysis, loses CO2. The resultant diazonium salt has been coupled with 2-naphthol. Similarly, 3-aminobenzo[i)]thiophene-2-carboxylic acid has been converted to the corresponding diazonium salt. This preferential loss of CO2 from or/Ao-diazonium carboxylates is unprecedented <89TL2345>. 

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