Difluorodiazoethane (CF₂ HCHN₂ ): A New Reagent for the Introduction of the Difluoromethyl Group

Difluorodiazoethane (CF₂ HCHN₂ ) is a small reactive diazoalkane. Its synthesis has been pursued since the 1970s, although only in the past three years have considerable advances been made. Today, difluorodiazoethane is a versatile reagent applied in [3+2]-cycloadditions, esterification, and carbene transfer reactions. Difluorodiazoethane possesses markedly altered reactivity compared to the well-studied trifluorodiazoethane (CF₃ CHN₂ ). In this article, we discuss the differences between the two reagents: CF₂ HCHN₂ and CF₃ CHN₂ . We highlight applications of difluorodiazoethane in organic synthesis, discuss bench-stable analogues, and its unexplored areas.