Dicarbonyl compounds diazo-coupling reactions

Compared to diazonium salts, diazo compounds are generally much less reactive towards nucleophiles than towards electrophiles. As a result of this azo coupling reactions of diazo compounds are the exception rather than the rule. Electron withdrawing substituents on the diazo carbon increase the reactivity towards nucleophiles. Consequently the ability to undergo azo coupling reactions increases from diazomethane to diazocarbonyl- and 2-diazo-l, 3-dicarbonyl compounds. Among the earliest reactions known were those with cyanide and sulfite ions Tertiary phosphines, as opposed to amines, can form stable addition complexes with diazoalkanes probably due to the ability of phosphorus to stabilize the betaine with its empty d orbitals (6). 

Azo coupling reactions are frequently observed in diazo transfer processes in which 4-toluenesulfonyl and other azides react with highly reactive methylene compounds, e. g., with dicarbonyl compounds (see Sect. 2.6, Schemes 2-56, 2-59, and 2-63). Such reactions were not, however, investigated mechanistically. Thus, although it is likely that alkanediazonium ions are intermediates, there is no direct evidence for their intermediacy. 

In general the reaction is conducted in aqueous solution under basic conditions—e.g. in the presence of KOH. The 1,3-dicarbonyl substrate is deprotonated to give the corresponding anion 5, which then couples to the arenediazonium species 1, to give the diazo compound 3 ... 

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