Chemo‐, Stereo‐ and Regioselective Fluoroallylation/Annulation of Hydrazones with gem‐Difluorocyclopropanes via Tunable Palladium/NHC Catalysis

Abstract

AbstractDefluorinative manipulation of polyfluorinated molecules has shown great promise due to its granting of synthetic versatility to inert C−F bonds. The development of chemo‐, stereo‐ and regioselective strategies to realize highly efficient formation of either the linear/branched or E/Z products from gem‐difluorocyclopropanes (gem‐F2CPs) is a challenging task. Herein, we have realized palladium/NHC‐catalyzed fluoroallylation/annulation of hydrazones with gem‐F2CPs that incorporate the hydrazone N2 moiety into the products. The thermodynamically unstable fluorinated E‐allylation products with aryl ketone hydrazones were obtained for the first time, while the di‐alkyl ketone hydrazones yielded the monofluorinated products with branched selectivity under similar reaction conditions. With aldehyde hydrazones, two kinds of pyrazoles were obtained via a defluorinative allylation/annulation cascade, in which different carbon atoms of gem‐F2CPs could be incorporated into the pyrazole rings regiospecifically. DFT calculations revealed that the divergent selectivity was kinetically controlled and the final C−C bond formation proceeded through a 7‐membered TS.