Rapid Epoxidation of α,β-Unsaturated Olefin in Microdroplets without Any Catalysts

Epoxy compounds are an important class of organic intermediates that are generally used to synthesize many important compounds and natural products. Herein, we carried out two-phase epoxidation of α,β-unsaturated olefins in microdroplets without any catalysts, where all the yield measurements were made upon microdroplet collection using high performance liquid chromatography. The epoxidation reaction can only take place under thermal irradiation both in microdroplets and in bulk phase, and an optimal yield was obtained in microdroplets at a reaction temperature of 35 °C. The epoxidation yield in microdroplets (85%) was superior over that in bulk phase (13%). In addition, the microdroplet epoxidation also produced configuration-selective epoxy compounds (only E-epoxides from the corresponding E-olefins and only Z-epoxides from the corresponding Z-olefins) compared to more byproducts (E-/Z-olefins and E-/Z-epoxides obtained from either E-olefins or Z-olefins) in bulk phase. It was attributed to E/Z configuration conversion under light irradiation in bulk phase, whereas such conversion was trivial in microdroplets. We also found that the epoxidation yields of trans-chalcones into their corresponding E-epoxides were apparently higher than cis-chalcones.