Photoredox-CatalyzedRadical Cyclization of UnactivatedAlkene-Substituted β‑Ketoesters Enabled Asymmetric TotalSynthesis of Tricyclic Prostaglandin D₂ Metabolite MethylEster

Regio- and stereoselective photoredox-catalyzed cyclizations of alkene-substituted β-ketoesters have been accomplished for the synthesis of polyfunctionalized cyclopentanones. This was achieved using 2,3,5,6-tetrakis(carbazol-9-yl)-1,4-dicyanobenzene (4CzTPN) and 2,4,6-triisopropyl-thiophenol as cocatalysts under illumination of a blue-light-emitting-diode at ambient temperature. The developed chemistry was successfully applied in the enantioselective total synthesis of the tricyclic prostaglandin D₂ metabolite (tricyclic-PGDM) methyl ester, which was completed in 9 steps with an overall yield of 7%.