Rh-catalyzed asymmetric cyclopropanation of benzofurans with trifluoromethyl N-triftosylhydrazones

An asymmetric dearomative cyclopropanation of benzofuran has been accomplished by a novel catalytic method that relies on using trifluoromethyl N-triftosylhydrazones as carbene sources in the presence of a chiral rhodium catalyst. This reaction produces chiral trifluoromethyl-tethered 2,3-disubstituted benzofuran cyclopropane, which carries versatile pharmacophores 2,3-dihydrobenzofuran and trifluoromethyl-substituted quaternary carbon centers. Notably, this process offers distinct advantages over other existing approaches due to being step economic and eliminating green-gas N2 as a harmless coproduct. DFT calculations explain the reason behind the high enantioselectivity during this cyclopropanation reaction.