Metal-Free Photoinduced Hydroalkylation Cascade Enabled by an Electron-Donor–Acceptor Complex

Abstract

A metal-and catalyst-free photoinduced radical cascade hydroalkylation of 1,7-enynes has been disclosed. The process is triggered by a SET event involving a photoexcited electron-donoraceptor complex between NHPI ester and Hantzsch ester, which decomposes to afford a tertiary radical that is readily trapped by the enyne. The method provides an operationally simple, robust and stepeconomical approach to the construction of diversely functionalized dihydroquinolinones bearing quaternary-centers. A sequential onepot hydroalkylation-isomerization approach is also allowed giving access to a family of quinolinones. A wide substrate scope and high functional group tolerance was observed in both approaches.

Progress in Photoinduced Radical Reactions using Electron Donor‐Acceptor Complexes

“…[163] Paixão et al disclosed a metal-/photocatalyst-free photoinduced radical cascade hydrolalkylation of 1,7-enynes for the synthesis of functionalized dihydroquinolinones enabled by an EDA complex between NHPI ester and Hantzsch ester under mild reaction conditions (Scheme 51). [164] The generation of EDA complex was analysed by UV/vis spectra and 1 H NMR. The possible mechanism is showed in Scheme 51.…”

Recent Advances on Photoinduced Cascade Strategies for the Synthesis of N‐Heterocycles

“…Under mild reaction conditions, our method showed high functional group tolerance and could be applied to a variety of tertiary NHPI esters furnishing a large family of dihydroquinolinones bearing quaternary centers, including moieties derived from commercially available drugs (Scheme 24a). Additionally, dihydroquinolinones derived from acrylic 1,7‐enines could be readily isomerized to the respective quinolinones, through a one‐pot reaction employing DBU and heating (Scheme 24b) [70] …”

“…Additionally, dihydroquinolinones derived from acrylic 1,7-enines could be readily isomerized to the respective quinolinones, through a one-pot reaction employing DBU and heating (Scheme 24b). [70] The mechanistic proposal for this transformation is outlined in (Scheme 25). A photoinduced SET event between NHPI-ester (104) and the diethyl 2,6-dimethyl-1,4-dihydropyridine-3,5-dicarboxylate (HE) might take place, leading to its fragmentation of to the tertiary-radical (XXXI).…”

Discovery of EDA-Complex Photocatalyzed Reactions Using Multidimensional Image Processing: Iminophosphorane Synthesis as a Case Study

“…6 Recently, the synthetic community has recognized the potential of this photochemical approach, mainly for dispensing the use of exogenous photoredox catalysts 6 . Examples of the synthetic potential of this approach include hetero-arene arylations, 4,5,[7][8][9] αalkylation of aldehydes, 10 hydrotri uoromethylation of unsaturated β-keto esters, 11 hydroalkylation of 1,7-enynes 12 and other chemical transformations. 6 Similar to the discovery of the EDA complex-mediated reactions, many other important chemical reactions have also been discovered serendipitously, such as the Friedel-Crafts and Wittig reactions.…”