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

Abstract

When irradiated with visible light, various cyclic, 2-alk-4-enyl-sub¬stituted 1,3-diketones underwent 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%) promoted the reaction. Addition of triisopropylthiophenol was required to secure high yields. The spirocyclization of a 2-alk-5-enyl-substituted substrate (m = 2) delivered a mixture of the seven-membered endo- and the six-membered exo-cyclization product.

Synthetic Applications of Photochemically Generated Radicals from Protic C(sp3)−H Bonds

“…Bach and co‐workers were intrigued by the potential of 1,3‐diketones to engage in an intramolecular [2+2] photocycloaddition. To their surprise, when 1,3‐diketones were subjected to visible light irradiation in the presence of thioxanthen‐9‐one (TXT) and 2,4,6‐triisopropylthiophenol (TRIPSH) as an HAT co‐catalyst the formation of spirocycles was observed, rather than the anticipated De Mayo‐type products (Scheme 39A) [81] . In this work, 11 examples of spirocyclization were reported in yields of 62–92 %.…”

“…To their surprise, when 1,3-diketones were subjected to visible light irradiation in the presence of thioxanthen-9-one (TXT) and 2,4,6-triisopropylthiophenol (TRIPSH) as an HAT cocatalyst the formation of spirocycles was observed, rather than the anticipated De Mayo-type products (Scheme 39A). [81] In this work, 11 examples of spirocyclization were reported in yields of 62-92 %. The scope consisted primarily of 1,3-cyclopentanedione (186) and 1,3-cyclohexanedione (187) spirocyclic derivatives.…”

“…A scope of 35 examples of CÀ H thiocyanation was reported in 40-95 % yield. Using this procedure, the authors disclose a broad array of β-ketoesters and 1,3-diketones capable of undergoing the reaction successfully including those bearing Michael acceptors (81), terminal alkynes (82), heterocycles (83), phosphonate (84), and thiolate ( 85) groups (Scheme 17B).…”

Efficient Radical‐Mediated Intermolecular α‐Alkylation Reactions of Carbonyl Compounds with Nonactivated Alkenes

“…A similar activation has also been reported for an intramolecular reaction. [74] In the same year, 2023, Wu et al developed colloidal quantum dots (QDs)-mediated catalytic α-alkylation reactions of cyclic ketones or α-pyridyl ketones with less-and nonactivated alkenes under visible-light irradiation (Scheme 19). QDs weakened the α-CÀ H bonds and formed α-carbonyl radical species under light irradiation.…”

Photoinduced Efficient Catalytic α-Alkylation Reactions of Active Methylene and Methine Compounds with Nonactivated Alkenes

“…Notably, this is an atom economically ideal alkylation process; however, available alkenes are limited to styrene derivatives. The alkylation reactions with nonactivated alkenes such as 1-decene were unsuccessful due to their low reactivity . To address this issue, here, we report our efforts to develop highly efficient catalytic α-alkylation reactions of active methylene and methine compounds with nonactivated alkenes using a newly developed photocatalyst and a Lewis acid/Brønsted base/hydrogen atom transfer (HAT) catalyst hybrid system.…”