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Updated: Sep 17, 2025

A Two-Step Protocol for Umpolung Functionalization of Ketones Via Enolonium Species
Published on: August 16, 2018
Photoredox-Catalyzed Formal [4 + 2] Cycloaddition of Pyridinium Masked Enols with Unactivated Olefins
Shisong Lv1, Jin Li1, Yuhui Hua1
1Shanghai Frontiers Science Center of Biomimetic Catalysis, Joint Laboratory of International Cooperation of Resource Chemistry of Ministry of Education, Shanghai Normal University, Shanghai 200234, China.
Abstract:
Herein, we developed a photoredox-catalyzed formal [4 + 2] cycloaddition of pyridinium-masked enols with unactivated olefins utilizing Ir(dF(Me)ppy)2(dtbbpy)PF6 as catalyst under blue light (455 nm) irradiation. A variety of pyridinium-masked enols and unactivated alkenes were examined to synthesize tetralones under optimal conditions. Through control and deuterium labeling experiments, it was suggested that the in situ generated α-carbon radical first attacked the alkene, forming a γ-carbonyl radical intermediate. This intermediate subsequently underwent intramolecular radical cyclization and deprotonation to produce the desired tetralones. This protocol facilitates the synthesis of functionalized tetralones under mild conditions, significantly enhancing the synthetic application of pyridinium-masked enols.
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