Photocyclization of enamines to access Spiroindolines and Spirooxindoles in continuous flow

We report an expedited flow chemistry approach to the catalyst/photosensitizer-free UV photocyclizations of aryl-enamines to afford spiroindolines. The photocyclizations occur under mild conditions and are tolerant to a variety of substituted aryl-enamines and spirocycle ring sizes. This flow protocol has a wide substrate scope and addresses the problems of irreproducibility and scalability of batch protocols. The utility of this reaction is demonstrated in a shortened formal synthesis of (±)-horsfiline.