Continuous Flow Synthesis of 2H-Thiopyrans via thia-Diels-Alder Reactions of Photochemically Generated Thioaldehydes

Herein, we report a novel protocol for the photochemical generation of thioaldehydes in a continuous flow process which were in situ reacted with electron rich 1,3-butadienes in thia-Diels-Alder reactions. A broad range of 3,6-dihydro-2H-thiopyrans were formed as products in much higher yields and productivities as compared to classical batch processes. Moreover, greatly reduced reaction times and a facile large-scale preparation of products were achieved by fully exploiting the advantages of continuous flow technology.