Continuous Preparation of Trifluoromethyl Diazomethane in Flow Using In-Line Membrane Phase Separation─Application to the Catalytic Asymmetric Cyclopropanation of Substituted Styrenes

Trifluoromethyl diazomethane (TFDM) is a versatile reagent in organic synthesis and medicinal chemistry efforts. The utility of TFDM is hampered by safety concerns on scale. A novel method for the generation of dry, acid-free concentrated solutions of TFDM in a flow is reported here. The inclusion of an in-line liquid–liquid phase separator was a critical component in the flow scheme. The resulting dry stream could be coupled to a reactor containing a chiral ruthenium catalyst and styrene substrate to enantioselectively construct trans-trifluoromethyl-substituted cyclopropanes in a plug flow reactor–batch train. This system was utilized to access a variety of enantioenriched trans-trifluoromethyl-substituted cyclopropanes.