Diazoalkanes, Diazoketones and Diazoesters

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). 

Carbanions derived from organometallic reagents react with aryldiazoalkanes diazoketones and diazoesters to yield hydrazones after hydrolysis (7). 

2-Diazo-l,3-dicarbonyl compounds are electrophilic enough to give azo coupling products with reactive aromatic azo coupling components as well as with CH acidic compounds such as P-diketones and p-keto-esters. 

Dicyanodiazomethane even gives an azo-coupling product with dimethyl-aniline (8) and also reacts with diaryldiazomethanes to give the mixed azines (9). 

Bisarylsulfonyldiazoraethanes can also react with diphenyldiazomethane and the azine is formed without passing through a carbene intermediate (10) 

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Depending on the fluonnating agent, diazoalkanes, diazoketones, and diazoesters can undergo hydrofluorination, halofluonnation, and geminal difluonnation reactions... 

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