Unexpected Course of the Reaction of 2‐Unsubstituted 1 H ‐Imidazole 3‐Oxides with Ethyl Acrylate

The attempted ethenylation at C(2) of 2‐unsubstituted 1 H ‐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 1 H ‐imidazole N‐ oxide and ethyl acrylate. The role of the catalyst is limited to the dehydration of the intermediate 3‐hydroxypropanoates to give 1 H ‐imidazol‐2‐yl‐substituted acrylates.