Olefin-Supported Cationic Copper Catalysts for Photochemical Synthesis of Structurally Complex Cyclobutanes.

The sole method available for the photocycloaddition of unconjugated aliphatic alkenes is the Cu-catalyzed Salomon–Kochi reaction. The [Cu(OTf)] 2 -benzene catalyst that has been standard in this reaction for many decades, however, is air-sensitive, prone to photodecomposition, and is poorly reactive towards sterically bulky alkene substrates. Using bench-stable precursors, we have designed an improved catalyst system with superior reactivity and photostability that offers significantly expanded substrate scope. The utility of this new catalyst for the preparation of sterically crowded cyclobutane structures is highlighted through the preparation of the cores of the natural products sulcatine G and perforatol.