Diazonium groups reactions

This elimination of the diazonium group is therefore a very valuable reaction, as it affords almost the only method by which nitro and primary amino groups directly attached to the benzene ring can be eliminated. 

The substitution of fairly labile nucleophilic groups (halogen, methoxy group) in the 3- and 5-positions, and the noncatalytic substitution of the diazonium group at C-4, are to be considered as nucleophilic substitution reactions. As in the benzenoid series, these reactions are believed to proceed in the former case by the Sx2 mechanism and in the latter by the SnI mechanism. 

Most functional groups do not interfere with the diazotization reaction. Since aliphatic amines are stronger bases and therefore completely protonated at a pH < 3, it is possible that an aromatic amino group is converted into a diazonium group, while an aliphatic amino group present in the same substrate molecule is protected as ammonium ion and does not react. ... 

The name Sandmeyer reaction - is used for the replacement of the diazonium group in an arenediazonium compound by halide or pseudohalide, taking place in the presence of a metal salt. However this is not a strict definition, since the replacement of the diazonium group by iodide, which is possible without a metal catalyst, is also called a Sandmeyer reaction. 

In a synthesis of minocycline, interesting use was made of a reductive alkylation of a nitro function, accompanied by loss of a diazonium group. The sequence provides a clever way of utilizing the unwanted 9-nitro isomer that arises from nitration of 6-demethyl-6-deoxytetracycline (//). When di-azotization was complete, urea and 40% aqueous formaldehyde were added, and the entire solution was mixed with 10% palladium-on-carbon and reduced under hydrogen. No further use of this combined reaction seems to have been made. 

The NH2 groups can be diazotized and reduced in the presence of thiosulphates and different metal ions. The effect of some metal ions, namely Fe ", Sn, Cu +, and Co on the graft yield of cotton modified with aryl diazonium groups via its reaction with 2,4-dichloro-6-(p-nitroaniline)-5-triazine in the presence of alkali and followed by reduction of nitro group was studied [4]. 

The diazonium group can be replaced by a number of groups. Some of these are nucleophilic substitutions, with SnI mechanisms (p. 853), but others are free-radical reactions and are treated in Chapter 14. The solvent in all these reactions is usually... 

Aryl Halides from Diazonium Ion Intermediates. Replacement of diazonium groups by halides is a valuable alternative to direct halogenation for the preparation of aryl halides. Aryl bromides and chlorides are usually prepared by a reaction using the appropriate Cu(I) salt, which is known as the Sandmeyer reaction. Under the classic conditions, the diazonium salt is added to a hot acidic solution of the cuprous halide.99 The Sandmeyer reaction occurs by an oxidative addition reaction of the diazonium ion with Cu(I) and halide transfer from a Cu(III) intermediate. 

As noted above, a convenient pathway to cinno-lines consists of intramolecular condensation of a diazonium group with a ketonic methyl group, or alternately with a double bond. The analogous reaction with an amide nitrogen leads to 1,2,3-benzotriazines, such as 198. Reaction of isatoic anhydride with N-aminomorpholine affords the hydrazide 196 then, treatment with nitrous acid yields initially the diazonium salt (197). Under the reaction conditions... 

The Mannich reaction provides an often-superior alternative to diazonium conjugation (Section 6.1, this chapter), because of the disadvantages inherent in the instability of both the diazonium group and the resultant diazo linkage. By contrast, conjugations done through Mannich condensations result in stable covalent bonds. 

Diazonium groups react with active hydrogens on aromatic rings to give covalent diazo bonds. Generation of a diazonium-reactive group usually is done from an aromatic amine by reaction... 

Ethyl 3-azido-l-methyl-177-indole-2-carboxylate 361 is prepared in 70% yield by diazotization of amine 360 followed by substitution of the created diazonium group with sodium azide. In cycloadditions with nitrile anions, azide 361 forms triazole intermediates 362. However, under the reaction conditions, cyclocondensation of the amino and ethoxycarbonyl groups in 362 results in formation of an additional ring. This domino process provides efficiently 4/7-indolo[2,3-i ]l,2,3-triazolo[l,5- ]pyrimidines 363 in 70-80% yield (Scheme 57) <2006TL2187>. 

A secondary reaction yields at the same time phenol ether by the replacement of the diazonium group by alkoxyl. This is clearly analogous to the conversion of diazonium salts to phenols. 

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. 

In a similar manner, nitrosation of t-Cys alkyl esters resulted in the formation of optically pure (5)-thiirane carboxylates 3. From the L-isomer the corresponding ( )-thiirane carboxylates were obtained. The reaction is interpreted as an 5 2 displacement of the diazonium group by the sulfur atom [76CC234 79JCS(P1)1852],... 

---