Sequential coupling of the transesterification of cyclic carbonates with the selective N-methylation of anilines catalysed by faujasites

Abstract

Anilines (R′C₆H₄NH₂: R′ = H, p-MeO, p-Me; p-Cl, and p-NO₂) react with a mixture of ethylene carbonate and methanol at 180 °C in the presence of alkali metal exchanged faujasites—preferably of the X-type—to give the corresponding N,N-dimethyl derivatives (R′C₆H₄NMe₂) in isolated yields up to 98%. Evidence proves that methanol is not the methylating agent. The reaction instead takes place through two sequential transformations, both catalyzed by faujasites: first transesterification of ethylene carbonate with MeOH to yield dimethyl carbonate, followed by the selective N-methylation of anilines by dimethyl carbonate. Propylene carbonate, is less reactive than ethylene carbonate, but it can be used under the same conditions. The overall process is highly chemoselective since the competitive reactions between the anilines and the cyclic carbonates is efficiently ruled out. Ethanol and propanol form the corresponding diethyl- and dipropyl- carbonates in the first step, but these compounds are not successful for the domino alkylation of anilines.