Difluorodiazoethane (CF2HCHN2): A New Reagent for the Introduction of the Difluoromethyl Group

Abstract Difluorodiazoethane (CF 2 HCHN 2 ) 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 (CF 3 CHN 2 ). In this article, we discuss the differences between the two reagents: CF 2 HCHN 2 and CF 3 CHN 2 . We highlight applications of difluorodiazoethane in organic synthesis, discuss bench‐stable analogues, and its unexplored areas.