Regio- and Stereoselective Cyclization Reactions of Unsaturated Silyl Enol Ethers by Photoinduced Electron Transfer – Mechanistic Aspects and Synthetic Approach

Sensitizer-controlled photochemical reactivity via upconversion of red light

“…38,49,116,[154][155][156] Fig. 8 Selected examples of different approaches to oxidative and reductive substrate activation with acridinium dyes and direct (monophotonic) blue/green light (a and b), 4,[140][141][142] direct excitation of DCA in the blue or green spectral range (c and d), 3,9,42,43,119 and two-catalyst systems operating under red light irradiation (e and f). 39 Overall redox-neutral reactions requiring an initial substrate oxidation step have been chosen on the right-hand side of the figure.…”

Organic Photoredox Catalysis

“…. 157 The main adducts of the reaction were cis-1-decalone systems (14.2) in all cases but one in which the alkene was disubstituted at the terminus. In that case, the product was the hexahydroindanone adduct.…”

“…Mattay and coworkers have done extensive investigations on the cyclization of pendant alkenes and alkynes on silyl enol ethers (14.1) employing DCA as the single electron photooxidant (Scheme 14). 157 The main adducts of the reaction were cis-1-decalone systems (14.2) in all cases but one in which the alkene was disubstituted at the terminus. In that case, the product was the hexahydroindanone adduct.…”

Total Synthesis of Sculponin U through a Photoinduced Radical Cascade Cyclization

“…Using 9,10‐dicyanoanthracene (DCA) as a photosensitizer, the Mattay group selectively induced an intramolecular 6‐ endo ‐trig cyclization of silyl enolates (e.g., 23 a – 23 e and 25 ) upon excitation with light at 450 nm, albeit in moderate to low yields (Scheme 3A). Importantly, neither the 5 ‐exo ‐trig cyclization nor a mixed 6‐ endo ‐trig/5 ‐exo ‐trig pathway was observed, despite their prevalence in classical radical cyclization [10a–d] . They inferred that the selectivity of 6‐ endo ‐trig cyclization over 5‐ exo ‐trig cyclization be ascribed to the relative stability of the newly formed secondary radical carbon with partially cationic character in the 6‐ endo ‐trig transition state, as its precursor could be a cationic radical of silyl enolate generated by PET [10g] .…”