Diazonium compounds, reaction with Subject

The synthesized CPMV-alkyne 42 was subjected to the CuAAC reaction with 38. Due to the strong fluorescence of the cycloaddition product 43 as low as 0.5 nM, it could be detected without the interference of starting materials. TMV was initially subjected to an electrophilic substitution reaction at the ortho-position of the phenol ring of tyrosine-139 residues with diazonium salts to insert the alkyne functionality, giving derivative 44 [100]. The sequential CuAAC reaction was achieved with greatest efficiency yielding compound 45, and it was found that the TMV remained intact and stable throughout the reaction. 

Diazonium ions react with all known nucleophiles. The addition of hydroxide, alkoxide, cyanide and sulfite ions does not belong to the subject of this review, but the formation of diazoamino compounds (1,3-triazenes) formed with ammonia, primary and secondary amines does. In analogy with the other reactions discussed in this paper, where carbon atoms are the site of attack by diazonium ions (C-coupling), these reactions are called N-coupling reactions. 

The initial intent to cover the subject exhaustively had to be abandoned because of the overwhelming amount of relevant literature. The following reactions are not covered but are briefly discussed, with references to reviews and seminal papers, in the section on Comparison with Other Methods reactions of carbanions and enolates and their surrogates with nitrogen oxides, nitrite and nitrate esters, and nitroso and nitro compounds reactions of enolates with diazonium salts, including the Japp-Klingemann reaction the diazo transfer reaction except as it interferes with the synthesis of azides the animation of boranes and the Neber rearrangement. 

Repeating the experiment with lb, but quenching the reaction by addition of diethyl ether as soon as the effervescence had subsided, afforded the tetrathiafulva-lenium salt 2b this compound was then subjected to solvolysis in undried deutero-acetone and afforded the corresponding alcohol 3b, consistent with its intermediacy in the reaction. The basic mechanism of the reaction can thus be represented by Scheme 2. Aryl radicals are formed following electron transfer to the diazonium cation and subsequent loss of dinitrogen. Rapid cyclization is followed by formation of the sulfonium salt 2b, and a facile solvolysis occurs to afford the alcohol 3b. Since the tertiary alcohol 3c was formed from substrate Ic, a similar pathway may have been followed, but the direct oxidation of the tertiary radical by electron transfer to a diazonium cation cannot yet be ruled out. The resistance of the primary salt to solvolysis is a classic hallmark of an Sn 1 reaction. (A refinement for the mechanism of the solvolysis step will be presented in Section 2.7.3.1 of this review, backed by very recent results). 

To conduct the substitution reactions of Figure 5.56, one neutralizes an acidic solution of the aromatic diazonium salt with diethylamine. This forms the diazoamino compound B (called a triazene ). It is isolated and subjected to the substitution reactions in an organic solvent. In each case, at first a leaving group is generated from the NIT, moiety of the dia-... 

Biological oxidation of a 2-aminoimidazole gives poor yields (<38%), and none at all with l-alkyl-2-aminoimidazoles. Nor will oxidation with peroxy-trifluoroacetic acid work It is, however, satisfactory for the oxidation of 4-aminoiniidazoles (which are usually rather unstable compounds). ITie most common way of making 2-nitroi midazoles is from the diazonium fluoro-borates subjected to the Gattermann reaction (see Section 7.3). Yields vary from 20 to 50% [6, 7], and again are dependent on the availability of the 2-aminoimidazoles (see Section 8.2.2). 

Several reviews have dealt with the photochemical reactions of the types of compounds included in this chapter. Alkynes, J. D. Coyle m The Chemistry of the Carbon-Carbon Triple Bond (Ed. S. Patai), Wiley, Chichester, 1978, p. 523 Nitriles, in The Chemistry of the Cyano Group, diazonium salts and diazo compounds by W. Ando, m The Chemistry of Diazonium and Diazo Groups (Ed. S. Patai), Wiley, Chichester, 1978, p. 341 and radiation chemistry by Z. B. Alfassi, m The Chemistry of Functional Groups, Supplement C(Eds. S. Patai and Z. Rappoport), Wiley, Chichester, 1983, p. 187. Azides have been the subject of another extensive review [E. F. Scriven and K. Turnbull, Chem. Rev., 88,298 (1988)]. In addition to these references, extensive information on the photochemical reactivity of such groups is to be found in the appropriate chapters in Volumes 1-24 of Photochemistry published by the Royal Society of Chemistry, London, from 1968-1993. 

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