Iodoarene-catalyzed one-pot preparation of 2,4,5-trisubstituted oxazoles from alkyl aryl ketones with mCPBA in nitriles

Abstract

2,4,5-Trisubstituted oxazoles could be easily prepared in moderate yields by the reaction of alkyl aryl ketones, iodoarene, m-chloroperbenzoic acid, and trifluoromethanesulfonic acid in acetonitrile, propionitrile, butyronitrile, and isobutyronitrile, respectively. Here, reactive aryliodonium I(III) species is formed in situ by the reaction of iodoarene with mCPBA and trifluoromethanesulfonic acid, and the formed aryliodonium I(III) species reacts with alkyl aryl ketone to form β-keto aryliodonium species. This in turn, reacts with nitrile to form the corresponding oxazole. Iodoarene works as a catalyst. However, one equivalent of iodoarene is required because one equivalent of reactive aryliodonium I(III) species must be formed prior to the reaction with alkyl aryl ketone. Then, by introducing an ionic liquid group into iodoarene, to form ionic liquid-supported iodoarene, the isolation procedure of oxazole could be simplified. The addition of ethyl acetate to the reaction mixture, washing of the reaction mixture with aq NaHCO 3, removal of ethyl acetate, and extraction of the residue with ether provided oxazoles in moderate purity, and the residual ionic liquid-supported iodoarene could be reused in the same reaction.