Photochemical [2 + 2] Cycloaddition of Alkenes with Maleimides: Highlighting the Differences between N -Alkyl vs N -Aryl Maleimides.

Throughout the last 15 years, there has been increased research interest in the use of light promoting organic transformations. [2 + 2] Cycloadditions are usually performed photochemically; however, literature precedent on the reaction between olefins and maleimides is limited to a handful of literature examples, focusing mainly on N -aliphatic maleimides or using metal catalysts for visible-light driven reactions of N -aromatic maleimides. Herein, we identify the differences in reactivity between N -alkyl and N -aryl maleimides. For our optimized protocols, in the case of N -alkyl maleimides, the reaction with alkenes proceeds under 370 nm irradiation in the absence of an external photocatalyst, leading to products in high yields. In the case of N -aryl maleimides, the reaction with olefins requires thioxanthone as the photosensitizer under 440 nm irradiation.