Safer and cheaper ways to carbenes

Metal carbenes are involved in cycloadditions, metatheses and C–H functionalizations. However, their main precursors are hazardous diazo compounds, which makes them unfit for industrial use. Recently, however, synthetic strategies overcame this limitation — enabling access to metal carbenes from aldehydes, carboxylic acids and alcohols.

Carbenes are an exception to the octet rule: they are neutral species containing a divalent carbon atom with six valence electrons, making them highly reactive. The synthesis of carbenes has traditionally required diazoalkanes as precursors. These compounds contain a diazo functional group that releases nitrogen upon thermal or photochemical activation or through coordination to transition metals, generating the corresponding carbene (box p. 82).

Carbenes from diazoalkanes

Although synthetic methods for diazoalkanes feature a low atom economy, they allow precise installation of the diazo group. This can be achieved through the Regitz diazo transfer reaction or by oxidation of the corresponding hydrazones. These methods tune carbene reactivity by placing the diazo group adjacent to electron-donating and electron-withdrawin

Wissenschaft + ForschungBlickpunkt Synthese