Compounds with Activated Methyl, Methylene and Methine Groups

1 Compounds with Activated Methyl, Methylene and Methine Groups 

Azo coupling reactions with activated C—H groups have been reviewed previously Generally the coupling of activated aliphatic carbon atoms with benzenediazonium ions is known as the Japp-Klingemann synthesis (30). 

The final product is usually the more stable hydrazone 63 or 64, formed either on tautomerization (R =H) or removal of one of the acyl groups (R = alkyl). The intermediate azo compound 62, however, can often be isolated, too. 

An interesting case of intramolecular azo coupling to an activated methyl group is the well-known synthesis of indazoles 72 starting from o-toluenediazonium salts 69 or from N-nitroso-N-acetyl-o-toluidine 67 . Recently the reaction mechanism (32) was elucidated When the reaction is run in the presence of D O or 

CH3COOD, no deuterium is incorporated in the diazonium salt 69. On the other hand, the synthesis of indazol 74 starting from the optically active diazonium salt 73 results in complete racemization (33). Therefore it can be concluded that the reaction 

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