Diazo transfer agent

The azo compound 24 is probably formed initially. It decomposes to give the vinyldiazonium ion 25 that in its turn couples with another molecule of 23 to give the final product 26 (13) Actually the diazodiester 22 acts as a diazo-transfer agent. 

The diazo keto ester 154 is prepared from the p-keto ester 153 using tosyl azide or p-NBSA.69,70 The diazo ester (156) could not be prepared by diazo transfer with TsN3/NEt3, since elimination usually occurs to yield acrylate.71 A diazo transfer agent, l-ethyl-2-azidopyridinium tetrafluoroborate, successfully converted isoindole keto ester (155) to diazo keto ester (156).71... 

Lastly, a-diazotization of ketophosphonium salts with azidinium tetrafluoroborate as a diazo group transfer agent has been described as a general process840 (reaction 258). 

The hazardous nature (see Tetrazoles below) of some alkyl azides limits the method in these cases, however A-alkyl- (benzyl) -1,2,3-triazoles can be obtained by preparing the azide in situ, for example using a mixture of sodium azide, the alkyne and a benzyl hahde in situ preparation of aryl azides is also feasible. An alternative method in which the alkyl azide is also generated in situ, is to use a diazo transfer to a primary amine the diazo transfer requires Cu(II) and the cycloaddition needs Cu(I) so a reducing agent is added together with the alkyne following the first phase. ... 

Scheme 16.18 Sequential one-pot procedure for diazo transfer and CuAiAC. First, diamine 71 is transformed to the corresponding diazide by Cu(ll)-catalyzed diazo transfer. After completion, Cu(l) required for subsequent CuAAC with 72 is generated by addition of reducing agent Na ascorbate. MW = microwave TBTA = tris(benzyltriazolylmethyl)amine...

Several important a-diazo ketones cannot be prepared via this approach however due to their base-sensitive nature. Danheiser and coworkers reported a detrifluoroacetylative diazo transfer strategy to combat this shortcoming. Deprotonation of substrate 52, followed by a trifluoroethyl trifluoroacetate (TFEA) quench furnished the trifluoroacetylated product. This undergoes facile detrifluoroacetylative diazo transfer from sulfonyl azide 54, to yield diazo ketone 53. In general they found TFEA to be superior to other trifluoroacetylating agents. 

Two methods for converting carboxylic acids to esters fall into the mechanistic group under discussion the reaction of carboxylic acids with diazo compounds, especially diazomethane and alkylation of carboxylate anions by halides or sulfonates. The esterification of carboxylic acids with diazomethane is a very fast and clean reaction.41 The alkylating agent is the extremely reactive methyldiazonium ion, which is generated by proton transfer from the carboxylic acid to diazomethane. The collapse of the resulting ion pair with loss of nitrogen is extremely rapid. 

There is now abundant evidence for the homolytic decomposition of covalent azo- and diazo-compounds of many types, but evidence for one-electron transfer reactions of diazonium salts is very scanty. Cooper (4) and Marvel ( ) have shown that reduction of diazonium salts by ferrous ions can initiate.vinyl polymerization, while Kornblum s work ( ) has shown that the reduction of diazonium salts by hypophosphite is promoted by oxidizing agents in a manner indicative of the chain reaction ... 

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