22 August 2007 (online)
Diazomethane (CH2N2, 1) is one of the most versatile and indispensable reagents in organic chemistry.  It is principally employed for the methylation of compounds containing active hydrogen, in cycloadditions, and one-carbon chain elongation/ring expansion. The main advantage of diazomethane over other methylating agents lies in its usage in neutral media, very often at low or room temperature, and in the absence of non-volatile byproducts.
Diazomethane is usually used as a solution in diethyl ether. It can be generated by reaction of alkali hydroxide with various derivatives of N-methyl-N-nitrosoamines, such as N-methyl-N-nitroso-4-toluenesulfonamide (Diazald®, 2), 1-methyl-3-nitro-1-nitrosoguanidine (MNNG, 3), or N-methyl-N-nitrosourea (4).
The structure of CH2N2 may be expressed by the following mesomeric forms to explain its basic (1a and 1b), electrophilic (1c), or nucleophilic character (1b).
- 1 e-EROS Encyclopedia of Reagents for Organic Synthesis John Wiley & Sons Ldt.; New York: 2006.
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