Photoinduced Rearrangement of Dienones and Santonin Rerouted by Amines

The photoinduced rearrangement pathways of simple 2,5‐dienones and the natural product santonin were found to be effectively rerouted by amines, giving rise to unprecedented products. Either cis olefins or cyclobutenes were obtained from 4,4‐disubstituted 2,5‐dienone upon irradiation (365 nm) in the presence of various amines depending on the solvent. Previously undescribed [4.4.0] and [5.3.0] fused‐ring‐containing products were obtained when santonin was irradiated (365 nm) in the presence of methylamine. The amines present in these reactions were incorporated into the products by means of amide‐group formation.