Dual Lewis Acid/Photoredox-Catalyzed Addition of Ketyl Radicals to Vinylogous Carbonates in the Synthesis of 2,6-Dioxabicyclo[3.3.0]octan-3-ones

Abstract

A combined Lewis acid/photoredox catalyst system enabled the intramolecular umpolung addition of ketyl radicals to vinylogous carbonates in the synthesis of 2,6-dioxabicyclo[3.3.0]octan-3-ones. This reaction proceeded on a variety of aromatic ketones to provide THF rings in good yield (up to 95%). Although diastereoselectivity was found to be modest (1.4-5:1) for the C-C bond forming reaction, the minor diastereomers were converted to 2,6-dioxabicyclo[3.3.0]octan-3-ones by an efficient Lewis acid-mediated epimerization cascade in up to 90% yield.

One-Pot Synthesis of Chromone-Fused Pyrrolo[2,1-a]isoquinolines and Indolizino[8,7-b]indoles: Iodine-Promoted Oxidative [2 + 2 + 1] Annulation of O-Acetylphenoxyacrylates with Tetrahydroisoquinolines and Noreleagnines

“…Upon completion, the solvent was removed under a vacuum. The resulting pale-yellow oil was purified by flash silica gel column chromatography (15:1 hexanes/EtOAc) to provide acetylphenoxy acrylates or acetylphenoxyacrylamides …”

Reductive annulations of arylidene malonates with unsaturated electrophiles using photoredox/Lewis acid cooperative catalysis

“…This is presumably due to the decreased electrophilicity of the vinylogous carbonate starting material due to hyperconjugation (Table 3). 19…”

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

“…It was expected that both electrophilic and nucleophilic functionalities formed through keto-enol tautomerism [10] of the aromatic b-ketoester would be able to interact with the photoexcited photocatalyst (PC*) to afford ketyl radical A [7,11] and the photocatalyst radical cation (PCC + ). [12] The higher electron affinity and lower LUMO energy of aromatic b-ketoesters compared to alphatic b-ketoester 1y [13] mean that the keto form rather than the enol form acts as an electron acceptor (Table S4 supported by the results of the DFT calculation in the Supporting Information; Scheme 1). Although the photocatalyst *fac-Ir(ppy) 3 (E 1/2 ox + Ir(ppy) 3 /*Ir(ppy) 3 = À1.73 V vs. SCE) [2a] is not able to carry out single-electron transfer (SET) to aromatic b-ketoester 1 a (E red < À1.90 V vs. SCE, E ox >+ 1.90 V vs. SCE in CH 3 CN, Figures S4 and S6), the anion 1 a À (E 1/2 ox 1 aC/1 a À =+ 0.66 V vs. SCE in DMF, Figure S5) [14] resulting from partially deprotonated 1 a would be oxidized by + fac-Ir(ppy) 3 species (E 1/2 red + Ir(ppy) 3 /Ir(ppy) 3 =+ 0.77 V vs. SCE) to regenerate fac-Ir-(ppy) 3 and simultaneously produce transient a-carbonyl radical B.…”