Unexpected course of the reaction of 2-Unsubstituted 1H-Imidazole 3-Oxides with Ethyl Acrylate

Abstract

The attempted ethenylation at C(2) of 2-unsubstituted 1H-imidazole N-oxides with ethyl acrylate (= prop-2-enoate) in the presence of Pd(OAc)2 does not occur. In contrast to the other aromatic N-oxides, the [2+3] cycloaddition of imidazole N-oxides predominates, and 3-hydroxyacrylates, isomeric with the cycloadducts, are key products for the subsequent reaction. The final products were identified as dehydrated 2+1 adducts of 1H-imidazole N-oxide and ethyl acrylate. The role of the catalyst is limited to the dehydration of the intermediate 3-hydroxypropanoates to give 1H-imidazol-2-yl-substituted acrylates.