Diazoalkanes

Diazoalkanes are organic compounds containing the diazo group attached to an alkyl or aryl carbon, typically written as R2C=N2. The simplest member is diazomethane, CH2N2. They are a subset of diazo compounds and are valued as precursors to carbenes; the diazo group readily extrudes nitrogen gas to generate a reactive carbene at the carbon center.

In many reactions, diazoalkanes participate in carbene-transfer chemistry, especially under the influence of metal catalysts such as rhodium, copper, or silver. Generated metal carbenes can engage in cyclopropanation of alkenes, insertion into C–H, O–H, or N–H bonds, and various cycloaddition processes. A related class, α-diazoketones, can undergo Wolff rearrangement upon heating or photolysis to form ketenes, illustrating another important transformation pathway for this chemistry.

Synthesis and handling of diazoalkanes are characterized by instability and energetic risk, so they are typically prepared and used under controlled, low-temperature conditions and often generated in situ from more stable precursors. Diazomethane is the most widely encountered example and is commonly employed for methylation of carboxylic acids to give methyl esters, as well as for other diazomethylation reactions. Due to their potential explosiveness and toxicity, diazoalkanes require careful handling, appropriate protective measures, and strict safety protocols.

Applications of diazoalkanes span broad areas of synthetic organic chemistry, where they provide versatile entry to carbenes and derived products, enabling a range of carbon–carbon and carbon–heteroatom bond-forming transformations.