Green epoxidation of unactivated alkenes via the catalytic activation of hydrogen peroxide by 4-hydroxybenzaldehyde

Abstract

In the quest for green, inexpensive and sustainable methods for the epoxidation of unactivated alkenes, for both academic and industrial applications, the interest in effective organocatalytic activators of hydrogen peroxide is gaining increased attention. In this work, we report the innovative use of a commercially available aldehyde, 4-hydroxybenzaldehyde, as an effective activator of H₂O₂ in a substoichiometric amount (20 mol%) for the selective epoxidation of alkenes. A plethora of alkenes were selectively epoxidised in very good to high yields. Thorough mechanistic studies revealed a novel, complex epoxidation mechanism involving a Payne/Dakin tandem pathway. 4-Hydroxybenzaldehyde seems to be mainly converted to hydroquinone/benzoquinone, which have been uncovered as efficient activators of hydrogen peroxide for the epoxidation of alkenes. This so far unidentified oxidative pathway may find new potential applications for oxidative transformations.