Diazo oxides carboxylic acids

With less electron-rich pyrroles, hydrochloric acid can be used in the diazotization. The diazo compounds were isolated after neutralization with aqueous ammonia [84H(22)2269]. 3-Diazo-2,5-diphenylpyrrole, although efficiently prepared by diazotization of the 3-aminopyrrole, can also be prepared by oxidation of the 3-nitrosopyrrole with dinitrogen trioxide (60JCS3270). Pyrrole-3-carboxylic acid, with buffered nitrous acid, gave the 3-diazo derivative 295 by displacement of the carboxyl group, together with the 3-diazo-2-carboxylic acid 296, obtained by further hydrolysis (62JCS1638) (Scheme 90). 

Imtdazo[4,5-c]pyridtne, 4,5,6,7-tetrahydro-synthesis, 5, 623, 640, 641 Imidazo[4,5-c]pyridine-6-carboxylic acid, 4,5,6,7-tetrahydro-synthesis, 5, 623, 641 Imidazopyridines as anthelmintic, 1, 202 synthesis, 5, 462 Imidazo[l,2-n]pyridines deuterium exchange, 5, 611 diazo coupling, 5, 614 Dimroth rearrangement, 5, 613 halogenation, 5, 611 hydrogenation, 5, 614 Mannich reaction, 5, 612 nitration, 5, 612 1-oxides... 

An a-diazo ketone 1 can decompose to give a ketocarbene, which further reacts by migration of a group R to yield a ketene 2. Reaction of ketene 2 with water results in formation of a carboxylic acid 3. The Woljf re arrangement is one step of the Arndt-Eistert reaction. Decomposition of diazo ketone 1 can be accomplished thermally, photochemically or catalytically as catalyst amorphous silver oxide is commonly used ... 

A carbon chain may be extended by one unit by using the Arndt-Eistert synthesis. In the first step, an acyl halide is treated with diazomethane to form the a-diazo ketone. This is then treated with water and silver oxide. The resultant product is the free acid. If an alcohol is used instead of water, then the related ester is formed. This is the best way of extending a chain by one unit if the carboxylic acid is available. The process of extension in this manner is called homologation. 

Carboxylic acids from diazo oxides with ring contraction... 

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