From aryldiazonium salts

Several examples of the mesoionic 3-aryl-l,2,3,4-oxatriazole-5-oxide ring system 123 have been prepared by cyclisation of the arylhydrazones 122 these in turn are prepared from aryldiazonium salts and bromonitromethane <99KGS413>. 

A number of catalytic conditions have been used for the reduction of 5-nitropyrimidines to amines using Pd or Raney-Ni. In the reduction of 4- and 5-nitrosopyrimidines, sodium dithionite is most commonly used. Hydrogenolysis of 5-arylazopyrimidines to form the 5-amino derivative is commonly done by catalytic hydrogenation. The 5-arylazopyrimidines are often prepared as intermediates in amination reactions. They are prepared from aryldiazonium salts, which couple with pyrimidines containing strongly electron-donating substituents [Pg.184]

This reaction also is apparently driven by the formation of the As=0 bond this involves formal oxidation of arsenic from the + 3 to the + 5 state. Arylarsonic acids are often obtained from aryldiazonium salts by the Bart reaction (p. 26) or... 

Using this methodology in 1896, Pschorr first reported the synthesis of phenanthrenes from the corresponding (Z)-2-styiylbenzenediazonium salts promoted by Cu+ [10]. Later, in 1924, Gomberg and Bachmann showed that biaryls could be prepared by intermolecular HAS from aryldiazonium salts and benzene [11]. However, yields were generally low (<40%), and many side reactions of diazonium salts were observed. 

Stewart MP, Maya F, KosynMn DV, Dirk SM, Stapleton JJ, McGuiness CL, Allara DL, Tour JM (2004) Direct covalent grafting of conjugated molecules onto Si, GaAs, and Pd surfaces from aryldiazonium salts. J Am Chem Soc 126 370-378... 

From I-Thioaldose Derivatives by Reaction with Aryldiazonium Salts. 183... 

Scheme 19 Aryldiazonium salt reacts spontaneously with H-Si(l 11) to afford modified Si(l 11) surfaces depending from the reaction conditions.

Aryldiazonium salts, usually obtained from arylamines, undergo replacement of the diazonium group with a variety of nucleophiles to provide advantageous methods for producing aryl halides, cyanides, phenols and arenes by reductive removal of the diazo group. Coupling reaction of aryldiazonium salts with phenols or arylamines give rise to the formation of azo dyes. 

Another approach to synthesizing pyrazolo[4,3-e]-l,2,4-triazines is by coupling ethoxycarbonylpyrazolones with aryldiazonium salts and subsequently cyclizing the resulting hydrazones e.g., the formation of 146 from 144 via 145 (76MI1). 

The main drawback to this reaction is the toxicity of diazomethane and some of its precursors. One possible alternative is the use of alkyltriazenes as reactive alkylating agents.52 Alkyltriazenes are readily prepared from primary amines and aryldiazonium salts.53 The triazenes, on being protonated by the carboxylic acid, generate a reactive alkylating agent that is equivalent, if not identical, to the alkyldiazonium ions generated from diazoalkanes. 

The authors also applied this procedure to a 90-member combinatorial library of 5,7-disubstituted-2-aryl-pyrimidotriazines 159 using the same set of l-cyano-3-(pyrimidin-4-ylamino)-2-methylisothiourea intermediates 158 (see Table 10/Scheme 27) with aryldiazonium salts derived from the range of arylamines A-O that is shown in Scheme 27. Isolated yields are shown in Table 10 for indicative amines A-E, and yield ranges are indicated in Scheme 27 for amines F-O <2004TL9319>. 

Cyclizations of aromatic diazonium salts138 (intramolecular Meerwein arylations) are pieparatively related to atom transfer reactions because a radical cyclization is terminated by the transfer of an atom or group other than hydrogen. However, the two methods are not mechanistically related. In the atom transfer method, the atom that is transferred to the cyclic product always derives from the radical precursor, but in the cyclizations of aryldiazonium salts, die atom or group transferred derives from an added reagent. This means that many different products can be prepared from a single diazonium precursor, but it... 

Three methods are commonly employed for the in situ preparation of organopalladium derivatives (i) direct metallation of an arene or heterocyclic compound with a palladium(II) salt (ii) exchange of the organic group from a main group organometallic to a palladium(II) compound and (iii) oxidative addition of an organic halide, triflate or aryldiazonium salt to palladium(O) or a palladium(O) complex. 

Aryldiazonium salts react with bis(dibenzylideneacetone)palladium to form arylpalladium salts and nitrogen. Therefore, diazonium salts may be employed to catalytically arylate alkenes under mild conditions. Since many aryl halides are made from diazonium salts this variation could even be more convenient than using aryl halides. The reaction proceeds in good to excellent yields in nonaqueous solvents, using sodium acetate as the base at room temperature with terminal alkenes and cyclopentene." Internal alkenes usually give poor yields, however. 

Arylhydrazono derivatives may be prepared from 4-oxo-6,7,8,9-tetrahy-dro-4H- or 9-formyl-4-oxo-1,6,7,8-tetrahydro-4//-pyrido [ 1,2-a]pyrimidine with aryldiazonium salts.307... 

The reaction of compound 90 with imidoyl halides without added base gives the hydrochloride salts of 1,2,4-thiadiazol-5-imines 95. The corresponding free bases can be liberated from the salts 95 with weak bases such as bicarbonate, but these imines are labile and decompose readily to form the W-cyanamide 96 and sulfur. The free base can be treated in situ with a second electrophile, such as an acid chloride, imidoyl chloride, or aryldiazonium salt, affording pentalene derivatives 97-99. It should be noted that the compound 98 cannot be prepared in a one-pot procedure from compound 90 and 2 equiv of imidoyl chloride in the presence of base, in contrast to the corresponding dioxa compound 91 (Scheme 22) <1981BSB89, 1992JHC1317>. 

Starting from the salts of the isomeric 1,2,4- and l,2,3-thiadiazol-5-imines, addition of aryldiazonium salts and base affords respectively fused thiapentaazapentalenes 99 and 178 that contain a 1,2,3,4-thiatriazole ring (Scheme 42) (see also Section 6.09.7.2) <1993JHC349, 1994J(P1)2895>. 

Similar reactions have been carried out with naphthalene and thiophene. The method has been employed only to a limited extent 23 since its discovery, probably because it involves the isolation of the dry diazonium salts and because a number of aryldiazonium salts (from o- and p-toluidine and /3-naphthylamine) gave no biaryls but only the corresponding aryl halides. 

An intermediate reduction of aryldiazonium salts Ar-N =N to the diazo radicals Ar-N=N also occurs when aryldiazonium salts react with KI to yield aryl iodides (Figure 5.55). Therefore, aryl radicals Ar are obtained under these conditions, too. Their fate, however, differs from that of the aryl radicals, which are faced with nucleophiles in the presence of Cu(II) (cf. Figure 5.53) or H3P02 (cf. Figure 5.54) the iodination mechanism of Figure 5.55 is a radical chain reaction consisting of four propagation steps. 

Fig. 5.55. Mechanistic aspects III of nucleophilic aromatic substitution reactions of aryldiazonium salts via radicals introduction of Nu = I through reaction of aryldiazonium salts with KI. In this (chain) reaction the radical I2 —apart from its role as chain-carrying radical—plays the important role of initiating radical. The scheme shows how this radical is regenerated the initial reaction by which it presumably forms remains to be provided, namely (1) Ar-N =N + I -> Ar- N=N + h ...

---