Light-Initiated\nFour-Step Domino-Multicomponent Synthesis\nof Functionalized Alkylidenecyclobutanes

A four-step domino-multicomponent reaction (domino-MCR)\nis described\nfor the synthesis of functionalized <i>E</i>-alkylidenecyclobutanes\nfrom 4-hydroxy-2-methylcyclopent-2-enone derivatives and three other\nsimple reagents. The domino-MCR is accomplished in a single protocol,\ncomprising a tandem photochemical [2 + 2]-cycloaddition/Norrish-I/γ-H\ntransfer reaction followed by an acetal protection and an allylic\nsubstitution reaction. In parallel, a consecutive process has been\nestablished with distinct photochemical and nonradiative sequences.\nAn intramolecular version of these reactions provides access to complex\nfused-bicyclic alkylidenecyclobutanes.