A novel synthesis of isocyanates and ureas via β-elimination of haloform

A novel synthesis of isocyanates via base-induced β-elimination of haloform from N-monosubstituted trihaloacetamides is described. The rate of reaction exhibits a strong dependence on the nature of the trihalomethyl group. Thus, while the reaction of tribromoacetamides proceeds at room temperature and the reaction of trichloroacetamides requires heating in polar solvents, no reaction could be observed for any of the corresponding trifluoro derivatives. This novel β-elimination of haloform from stable and readily available trihaloacetamides was applied to a 'one-pot' synthesis of ureas which avoids the use of phosgene and isolation of isocyanates.