Reaction of Aromatic N-Oxides with Dipolarophiles. XV. Formation of the 1, 5-Sigmatropy Products and Their Double Ene Reaction Products

Abstract

In connection with the pericyclic reaction of 3, 5-dimethylpyridine N-oxide with N-substituted maleimides, the structure of a 1, 5-sigmetropy product was determined by the X-ray crystallographic method. In the reaction of 2-alkylpyridine N-oxides with N-substituted maleimides, we have isolated a series of 1 : 3 ene reaction products of a new type.The primary exo cycloadducts readily transform into the endo 1, 5-sigmatropic rearrangement products, which again react with two molecules of N-substituted maleimide to give the 1 : 3 ene reactio products. The observed reaction behavior and plausible reaction pathways are discussed in terms of frontier molecular orbital considerations.