Photochemical Cyclopropenation of Alkynes with Diazirines as Carbene Precursors in Continuous Flow.

An efficient synthesis of 3-trifluoromethyl-3-aryl-cyclopropenes via the cyclopropenation reaction of alkynes with photolytically generated carbenes from diazirine compounds is described. This reaction is performed in continuous flow using readily available LEDs under mild reaction conditions. This new and efficient method describes the synthesis of 25 examples of 3-trifluoromethyl-3-aryl-cyclopropenes with yields up to 97%, achieved in continuous flow with a 5 min residence time. Control experiments highlighted that diazirines are more efficient than diazo compounds for this transformation.