Diazomethane, Carbenes, and Cyclopropane Synthesis

Diazomethane forms methylene, which converts alkenes into cyclopropanes 

The unusual substance diazomethane, CH2N2, is a yellow, highly toxic, and explosive gas. It decomposes on exposure to light, heat, or copper metal by loss of N2. The result is the highly reactive species methylene, H2C , the simplest carbene. 

When methylene is generated in the presence of compounds containing double bonds, addition takes place to furnish cyclopropanes. The process, another Lewis acid-base addition, is usually stereospecific, with retention of the original configuration of the double bond. 

Diazomethane is the simplest member of the class of compounds called diazoalkanes or diazo compounds, R2C=N2. When diazo compound A is irradiated in heptane solution at -78°C, it gives a hydrocarbon, C4H6, exhibiting three signals in H NMR and two signals in C NMR spectroscopy, all in the aliphatic region. Suggest a structure for this molecule. 

Halogenated carbenes and carbenoids also give cyclopropanes 

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Diazomethane, Carbenes, and Cyclopropane Synthesis Preparing three-membered rings. 

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