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.