Nitrenes and Nitrenoids The Curtius Rearrangement

Certain diazo compounds, however, do not require a transition-metal catalyst in order to react with carbon-carbon double bonds. Diazomethane itself acts as a 1,3-dipole and undergoes 1,3-dipolar additions with alkenes. The pyrazoline intermediate initially produced loses N2 to produce a cyclopropane  

Provided it works (which is not always the case), this transition-metal-free reaction may be viewed as a greener alternative to traditional metal-catalyzed cyclopropanation protocols. 

Trimethylsilyldiazomethane is obtained via the interaction of trimethylsilylmethyl-magnesium chloride and diphenyl phosphorazidate (DPPA), as shown below  

Note The organomagnesium starting material is obtained via a standard Grignard synthesis  

Nitrenes are monovalent nitrogen compounds with a zero formal charge on the nitrogen. They are subvalent in the sense that the nitrene nitrogen has only six electrons in its valence 

---