Diazo compounds are used as precursors to carbenes, which are generated by thermolysis or photolysis, for example in the Wolff rearrangement. They are also used in transition metal-catalyzed cyclopropanation reactions for example in a synthesis of tranylcypromine in scheme 1 in which the sodium salt of benzaldehyde tosyl hydrazone is converted to a rhodium metal carbene through the diazo intermediate.
An unusual biomolecule sporting a diazo group was synthesized in 2006 with in its final stage the reaction of a carbonyl group with the hydrazine 1,2-bis(tert-butyldimethylsilyl)hydrazine to the hydrazone followed by reaction with the periodinane difluoroiodobenzene to the diazo compound
Another commercially relevant diazocompound is Ethyl diazoacetate N2CHCOOEt.
A group of isomeric compounds with similar properties are the diazirines, where the carbon and two nitrogens are linked as a ring.