Metal-Free Perfluoroarylation by Visible Light Photoredox Catalysis

Abstract

Visible light and eosin Y catalyze the direct arylation of simple arenes with fluorinated aryl bromides by a photoredox process. The reaction scope is broad in fluorinated compounds and arenes and the general and simple procedure provides a metal-free alternative for the synthesis of synthetically valuable polyfluorinated biaryl structures. The mild reaction conditions allow a selective reaction with the alkaloid brucine without protection of functional groups illustrating the potential of the process for late stage functionalization. Mechanistic investigations reveal the photoreduction of eosin Y via its triplet state by triethylamine and subsequent electron transfer from the eosin Y radical anion to the polyfluorinated bromoarene, which fragments into the polyfluorinated aryl radical and a bromide anion. A radical chain reaction mechanism was excluded by a quenching factor analysis.

Organic Photoredox Catalysis

“…487 This C−H arylation reactivity is derived from the reductive cleavage of perfluoroaryl bromide to form perfluoroaryl radicals such as 154.2, which add to arenes and heteroarenes to ultimately furnish the cross-coupled products, although the regioselectivity of the addition is variable. Mixtures of o-, m-, and p-isomers were obtained for monosubstituted arene coupling partners which were employed in 20-fold excess (e.g.…”

Dual C–F, C–H Functionalization via Photocatalysis: Access to Multifluorinated Biaryls

“…H 20 on one or both partners) have also been developed ( Approach B ). 21–23 Typically, activated multifluorinated arenes are derived from the C–F bond in 1–3 steps, i.e. C–F to C–H 24 to C–halogen 25,26 to C–organometallic.…”

Organic Reactions Promoted by Metal-Free Organic Dyes Under Visible Light Irradiation

“…Eosin Y (EY) is the typical organic dye to induce the synthetically useful photoredox transformations [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30]. EY that absorbed visible light populates in the lowest excited singlet state.…”

“…Final deprotonation gives the coupling product 2. Next, the EY-catalyzed arylation of simple arenes with fluorinated aryl bromides was developed [15]. In the presence of EY (5 mol%) and triethylamine as an electron donor, the direct arylation using 1-bromo-2,3,4,5,6-pentafluorobenzene 3 and benzene gave the coupling product 4 in 85% yield.…”