A stable intermediate: a new insight into the mechanism of Lewis acids-promoted formation of acylals from aldehydes

Treatment of m-nitrobenzaldehyde with acetic anhydride in the presence of Lewis acids, such as InBr3, ZnBr2, Cu(OTf)2, gives a stable intermediate at the initial stage of reaction. Based on this new organic compound characterized by X-ray single crystal diffraction, a new mechanism for Lewis acids-promoted formation of acylals from aldehydes is proposed. Exchange reaction with different ratio of acetic anhydride to propionic anhydride, in the presence of Lewis acids, is studied.