Photocatalytic Spirocyclization of 2-Alk-ω-enyl-Substituted Cycloalkane-1,3-diones

When irradiated with visible light, various cyclic 2-alk-4- enyl-substituted 1,3-diketones undergo an intramolecular endo-addition (m = 1) onto the double bond resulting in spirocyclic products (11 examples, 62-92% yield). Both an organic (TXT: thioxanthone, 20 mol%) and an organometallic Ir-based photocatalyst (5 mol%) promote the reaction. Addition of triisopropylthiophenol is required to secure high yields. The spirocyclization of a 2-alk-5-enyl-substituted substrate (m = 2) delivers a mixture of the seven-membered endo- and the sixmembered exo-cyclization products.