Photochemically Produced Aminocyclobutanes as Masked Dienes in Thermal Electrocyclic Cascade Reactions

Cyclobutane products of a triplet sensitized enamide-alkene intramolecular [2+2] photocycloaddition have been shown to undergo fragmentation under acidic conditions. This lability has been exploited by inducing a complexity generating thermal electrocyclic cascade sequence involving the in situ formation of a cyclobutene, followed by electrocyclic ring opening, Diels-Alder cycloaddition and subsequent lactamization. This combination of excited state photochemistry and thermal elec-trocyclic cascade reactions allows simple planar molecules to be rapidly transformed into sp3 rich scaffolds.