Diazo electron-transfer products

Complexed arenediazonium salts are stabilized against photochemical degradation (Bartsch et al., 1977). This effect was studied in the former German Democratic Republic in the context of research and development work on diazo copying processes (Israel, 1982 Becker et al., 1984) as well as in China (Liu et al., 1989). The comparison of diazonium ion complexation by 18-crown-6 and dibenzo-18-crown-6 is most interesting. Becker at al. (1984) found mainly the products of heterolytic dediazoniation when 18-crown-6 was present in photolyses with a medium pressure mercury lamp, but products of homolysis appeared in the presence of dibenzo-18-crown-6. The dibenzo host complex exhibited a charge-transfer absorption on the bathochromic slope of the diazonio band. Results on the photo-CIDNP effect in the 15N NMR spectra of isotopically labeled diazonium salts complexed by dibenzo-18-crown-6 indicate that the primary step is a single electron transfer. 

The carbon dioxide anion-radical was used for one-electron reductions of nitrobenzene diazo-nium cations, nitrobenzene itself, quinones, aliphatic nitro compounds, acetaldehyde, acetone and other carbonyl compounds, maleimide, riboflavin, and certain dyes (Morkovnik and Okhlobystin 1979). The double bonds in maleate and fumarate are reduced by CO2. The reduced products, on being protonated, give rise to succinate (Schutz and Meyerstein 2006). The carbon dioxide anion-radical reduces organic complexes of Co and Ru into appropriate complexes of the metals(II) (Morkovnik and Okhlobystin 1979). In particular, after the electron transfer from this anion radical to the pentammino-p-nitrobenzoato-cobalt(III) complex, the Co(III) complex with thep-nitrophenyl anion-radical fragment is initially formed. The intermediate complex transforms into the final Co(II) complex with the p-nitrobenzoate ligand. 

There are several aspects of electron transfer reactions to and from diazo compounds First, the processes in an electrochemical cell, in particular those taking place at the surfaces of the cathode and the anode second, the structure of the intermediates and final products obtained in electrochemical processes third, reactions of diazo compounds carried out with inorganic and organic reduction or oxidation reagents. 

The complexity of product formation by electron transfer from the diazo compound to the electrode is also evident in preparative electrochemical oxidations of diazoalkanes (see review by Fry, 1978). We have already mentioned the investigation of Elofson et al. (1974) in sulfolane because electron transfer to diazomethane did not occur. Yet, electrochemical oxidation in the presence of pyridine was successful and yielded A -methylpyridinium perchlorate. The mechanism suggested by Elofson has been questioned by Fry (1978, p. 496). 

The diazo transfer reaction with sulfonyl azides has been extensively used for the preparation of diazo compounds with two electron-withdrawing groups (equation 1 ).28 Toluenesulfonyl azide (13a)29 is the standard reagent used, but due to problems of safety and ease of product separation, several alternative reagents have been developed recently. n-DodecylbenzenesuIfonyl azide (13b)30 is very effective for the preparation of crystalline diazo compounds, while p-acetamidobenzenesulfonyl azide (13c)31 or naph-thalenesulfonyl azide (13d)30 are particularly useful with fairly nonpolar compounds. Other useful reagents are methanesulfonyl azide (13e)32 and p-carboxybenzenesulfonyl azide (13f).33... 

A select number of transition metal compounds are effective as catalysts for carbenoid reactions of diazo compounds (1-3). Their catalytic activity depends on coordination unsaturation at their metal center which allows them to react as electrophiles with diazo compounds. Electrophilic addition to diazo compounds, which is the rate limiting step, causes the loss of dinitrogen and production of a metal stabilized carbene. Transfer of the electrophilic carbene to an electron rich substrate (S ) in a subsequent fast step completes the catalytic cycle (Scheme I). Lewis bases (B ) such as nitriles compete with the diazo compound for the coordinatively unsaturated metal center and are effective inhibitors of catalytic activity. Although carbene complexes with catalytically active transition metal compounds have not been observed as yet, sufficient indirect evidence from reactivity and selectivity correlations with stable metal carbenes (4,5) exist to justify their involvement in catalytic transformations. 

The formation of thioethers as by-products occurs because the triazolo-pyridines are in equilibrium with a diazo form, and the position of the equilibrium depends on the substitution pattern on triazolopyridine (050BC3905). The presence of an electron-withdrawing sulphoxide in position 6, as is the case in 98 or 99, shifts the equUibrium to the diazo form. The formation of thioethers 104 and 105 from the diazo form, can be explained on the assumption that a carbene intermediate formed by extrusion of nitrogen (07ARK297) is trapped by an oxygen transfer from the corresponding sulphoxide (67TL2363), which is reduced to a thioether (Scheme 21). 

Related Reagents, p-toluenesulfonyl azide and methane-sulfonyl azide have been used widely for diazo transfer to stabilized enolates. The latter reagent simplifies isolation of the desired product, but is potentially explosive and must be handled with care. Relative to other aryl analogs, the electron-deficient p-nitrobenzenesulfonyl analog favors diazo transfer to imide enolates. ... 

A study of reactions of benzocyclic jS-keto esters with sulfonyl azides has provided further indication, from results for a benzosuberone, that the electronic features of the azide can profoundly influence the distribution of azidation, diazo transfer, and ring contraction products. 

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