Dibromomethane as one-carbon source in organic synthesis: a versatile methodology to prepare the cyclic and acyclic α-methylene or α-keto acid derivatives from the corresponding terminal alkenes

Ozonolysis of mono-substituted alkenes followed by reacting with a preheated mixture of CH2Br2–Et2NH affords α-substituted acroleins in good yields. Under very mild reaction conditions, these α-substituted acroleins can be easily converted to α-methylene esters , which could be further converted to the corresponding α-keto esters . This methodology can be also applied to the preparation of α-methylene lactones , α-methylene lactams, and α-keto lactones with various ring sizes.