Addition of diazomethane to carbonyl groups

The first step in the reaction of diazomethane with an aldehyde or a ketone, known as the Arndt-Eistert reaction, is addition of the diazomethane to the carbonyl group  

The diazonium betaines formed are sometimes reasonably stable. The rearrangements which occur with evolution of nitrogen and formation of homologous ketones or aldehydes are described in detail on page 1092 it suffices in this Section to mention the formation of oxiranes (epoxides), which can also occur on evolution of nitrogen  

This epoxide formation takes place almost exclusively when R is an electron-attracting group e.g., 2-(trichloromethyl)oxirane is obtained from chloral and diazomethane,174 and 2-(o-nitrophenyl)oxirane from o-nitrobenzalde-hyde.175,176 

If R is an electron-repelling group, oxirane formation is less evident and the rearrangements discussed on page 1092 provide the products. 

Addition of Grignard reagents and other organometallic compounds177 

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