N-hydroxyphthalimide Catalyzed Epoxidation of Inactive Aliphatic Olefins with Air at Room Temperature

Metal-free aerobic epoxidation of aliphatic alkenes especially terminal alkenes, remains a significant challenge. Herein, a novel and practical synthetic method with N-hydroxyphthalimide (NHPI) as catalyst, isobutyraldehyde as sacrificial reductant and air as oxidant has been developed for the epoxidation of olefins in excellent to moderate conversions and selectivity at room temperature. Meanwhile, this synthetic methodology could efficiently convert inactive light olefins to corresponding epoxides which are highly desired in industry. Moreover, several free radicals in the reaction were identified and characterized by in situ electron paramagnetic resonance spectroscopy (in situ EPR) and high-resolution mass spectrometry (HRMS). Mechanistic studies showed that the phthalimide N-oxyl radical (PINO) generated from NHPI would promote the homolysis of isobutyraldehyde to carbonyl carbon radical by the extraction of hydrogen atoms.