Photoredox-Catalyzed Oxidation of Anions for the Atom-Economical Hydro-, Amido-, and Dialkylation of Alkenes

Photoredox-Catalyzed Hydroalkylation of C(sp3)-H Acids

We present a detailed study on a photoredox catalysis platform that directly engages 1,3-dicarbonyl C(sp3)-H acids toward radical reactions. This platform enables redox-neutral hydroalkylation and cross-coupling, as well as oxidative transformations that demonstrably improve on the prior state of the art. Herein, we present interrogations of the underlying catalytic cycle and mechanism for this platform through kinetic, thermodynamic, and computational studies. The present investigations also demonstrate the key role of lithium trifluoroacetate under complementary Ce-containing and Ce-free photoredox conditions to enable ligand-to-metal charge transfer (LMCT) or multi-site proton-coupled electron transfer (MS-PCET) activations, respectively.

Photoredox-Catalyzed Radical Cyclization of Unactivated Alkene-Substituted β-Ketoesters Enabled Asymmetric Total Synthesis of Tricyclic Prostaglandin D2 Metabolite Methyl Ester

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%.

Iron-Mediated Dialkylation of Alkenylarenes with Benzyl Bromides

We disclose a method for the dibenzylation of alkenylarenes with benzyl bromides using iron powder. This reaction generates branched alkyl scaffolds adorned with functionalized aryl rings through the formation of two new C(sp3)-C(sp3) bonds at the vicinal carbons of alkenes. This protocol tolerates electron-rich, electron-neutral, and electron-poor benzyl bromides and alkenylarenes. Mechanistic studies suggest the formation of benzylic radical intermediates as a result of single-electron transfer from the iron, which is intercepted by alkenylarenes.

Photoinduced Copper-Catalyzed Aminoalkylation of Amino-Pendant Olefins

The combination of photo and copper catalysts has emerged as a novel paradigm in organic catalysis, which provides access to the acceleration of chemical synthesis. Herein, we describe an aminoalkylation of amino-dependent olefins with maleimides through a cooperative photo/copper catalytic system. In this report, the strategy allows the generation of a broad complex of functionalized nitrogenous molecules including oxazolidinones, 2-pyrrolidones, imidazolidinones, thiazolidinones, pyridines, and piperidines in the absence of an external photosensitizer and base. The approach is achieved through a photoinduced Cu(I)/Cu(II)/Cu(III) complex species of nitrogen nucleophiles, intermolecular radical addition, and hydrogen atom transfer (HAT) processes. The plausible mechanism is investigated by a series of control experiments and theoretical tests, including radical scavenging experiments, deuterium labeling experiments, ultraviolet-visible absorption, and cyclic voltammetry (CV) tests.