Liquid-Liquid Slug-Flow-Accelerated [2+2] Photocycloaddition of Cinnamates

[2+2] photocycloaddition of cinnamates, using a previously described cone reactor and a bis-thiourea catalyst, is greatly accelerated by employing liquid-liquid slug flow. In most cases, a four-fold acceleration in reaction time was observed with equivalent or superior yields. This approach has enabled significant improvement in the reaction throughput and expansion of the substrate scope to include challenging substrates. It has also enabled, to our knowledge, the first reported direct photodimerization in solution of electron-rich cinnamamide substrates.