N-Heterocyclic Carbene Catalyzed Cross Dehydrogenative Coupling of Aldehydes with Methanol: Combined Use of Eosin Y and Hexachloroethane

Abstract

AbstractCross dehydrogenative coupling of aldehydes with methanol was investigated under organocatalytic conditions based on the cooperation­ between N-heterocyclic carbene and eosin Y·Na as an organophotocatalys­t. The combined use of eosin Y·Na and hexachloro­ethane (C2Cl6) was the effective method for the oxidative esterification of various aldehydes, because the oxidation steps are promoted by two pathways associated with the activated photocatalyst and C2Cl6. In contrast, the combined use of eosin Y·Na and bromotrichloromethane (BrCCl3) was effective only for the oxidative esterification of simple cinnamaldehyde derivatives, in which BrCCl3 promotes the oxidation as a brominating reagent toward radical intermediates.