Synthesis of aryl fluorocyclopropanes from aryl fluorodiazirines and alkenes in continuous flow.

Photochemically induced generation of aryl fluorocarbenes from aryl fluorodiazirines and their subsequent [2+1] cycloaddition with alkenes was developed in continuous flow. The generated electrophilic aryl fluorocarbene reacted with a range of alkenes enabling the synthesis of the corresponding 3-fluoro-3-aryl-cyclopropanes in a 5-minute residence time under 380-nm LED irradiation in continuous flow (20 examples). The scaled-up reaction of 3-fluoro-3-(4-chlorophenyl)-3-diazirine with styrene under irradiation at 380 nm led to the fluorocyclopropane with a 77% yield, providing a throughput yield of 0.945 g h.