Photoredox Catalysis of Aromatic β‐Ketoesters for in Situ Production of Transient and Persistent Radicals for Organic Transformation

Abstract

Radical formation is the initial step for conventional radical chemistry. Reported herein is a unified strategy to generate radicals in situ from aromatic β‐ketoesters by using a photocatalyst. Under visible‐light irradiation, a small amount of photocatalyst fac‐Ir(ppy)3 generates a transient α‐carbonyl radical and persistent ketyl radical in situ. In contrast to the well‐established approaches, neither stoichiometric external oxidant nor reductant is required for this reaction. The synthetic utility is demonstrated by pinacol coupling of ketyl radicals and benzannulation of α‐carbonyl radicals with alkynes to give a series of highly substituted 1‐naphthols in good to excellent yields. The readily available photocatalyst, mild reaction conditions, broad substrate scope, and high functional‐group tolerance make this reaction a useful synthetic tool.

Magnetically modulated photochemical reaction pathways in anthraquinone molecules and aggregates

“…The photochemical reactions have been encouraging the development of synthetic chemistry during past decades, as the excited-state molecules can undergo transformations that are significantly distinctive from those of ground state (Lang et al, 2014;Mou et al, 2019;Yang et al, 2020;Zhou and Zhang, 2020). In addition to the higher energy level than the ground state, the excited state usually has both singlet and triplet characteristics of spin1/2 pair (Miura et al, 2017), which allows for the observation of magnetic field effects (MFEs) on a series of photochemical systems (Buchachenko and Lawler, 2017;Chesta et al, 2007;Okazaki et al, 1996).…”

Single Electron Activation of Aryl Carboxylic Acids

“…The recent development of visible light photocatalysis has found widespread application for the generation of active radical species (Yang et al, 2020;Ravelli et al, 2016;Li et al, 2018;Huo et al, 2014;Huang et al, 2020aHuang et al, , 2020bYu et al, 2020). In 2015, the group of Gonzalez-Gomez demonstrated an elegant visible light photocatalytic dehydrogenative lactonization of 2-arylbenzoic acids by using [Acr + -Mes] (E 1/2 red = +2.06 vs SCE) as a photocatalyst in the presence of (NH 4 ) 2 S 2 O 8 as the oxidant (Scheme 6) (Ramirez et al, 2015).…”

Cs+/Alcohol Promoted[4C+2C]Annulation: ASynthetic Strategy for Polysubstituted Phenols

“…The synthesis of arenes, including phenols, has attracted much attentions with the modification of an existed arene substrate or through benzannulation reactions of acyclic building blocks. [1][2][3][4][5] Benefiting from the fruitful functionalities of acyclic precursors, the benzannulation reactions can provide versatile substitution patterns and overcome the formation of by-products encountered in the modification of existed arenes, especially by multistepsynthesis. As useful building blocks, ketene dithioacetals [6][7][8][9] have been investigated in depth, for example, in the construction of a wide variety of carbo-/heterocyclic compounds and the construction of polysubstituted arenes and heteroaromatics via [7 + 1], [5 + 1], [4 + 2], [3 + 3], [4 + 1 + 1], [3 + 1 + 1] annulation.…”