Decarboxylative Fluorination of Aliphatic Carboxylic Acids via Photoredox Catalysis

Abstract

The direct conversion of aliphatic carboxylic acids to the corresponding alkyl fluorides has been achieved via visible light-promoted photoredox catalysis. This operationally simple, redox-neutral fluorination method is amenable to a wide variety of carboxylic acids. Photon-induced oxidation of carboxylates leads to the formation of carboxyl radicals, which upon rapid CO2-extrusion and F• transfer from a fluorinating reagent yield the desired fluoroalkanes with high efficiency. Experimental evidence indicates that an oxidative quenching pathway is operable in this broadly applicable fluorination protocol.

Electron donor-free photoredox catalysis via an electron transfer cascade by cooperative organic photocatalysts

“…Recent research activities have demonstrated a vast number of structural design methods of small molecular 8,10,[16][17][18][19][20] or macromolecular [21][22][23][24][25][26][27][28][29][30] OS systems as efficient photocatalysts for visible light-promoted photoredox reactions. Nevertheless, most developed OS photocatalysts, similar to traditional transition metal complexes, [31][32][33][34][35][36][37][38] are single photocatalytic systems. As illustrated in Fig.…”

Transition-metal-free visible-light photoredox catalysis at room-temperature for decarboxylative fluorination of aliphatic carboxylic acids by organic dyes

“…As a result, the fluorine atom would transfer from oxidizing Selectfluor to the alkyl radical. [9] The mechanistic pathway, which is very different from previous work, [8a, 9] has a great significance for the research of decarboxylative reaction catalyzed by organic photocatalyst via visible light. In conclusion, we have developed an efficient, general and green method for decarboxylative fluorination of aliphatic carboxylic acids in aqueous solution with organic dyes as transition-metal-free photocatalyst, affording monofluoroalkanes, aryl monofluoroalkyl ethers or fluoroesters in good to excellent yields.…”

“…[8a] Very recently, MacMillan group reported elegant decarboxylative fluorination with Ir[dF(CF3)ppy]2(dtbbpy)PF6. [9] Li's work: We hypothesized that organic photoredox catalyst might be utilized in decarboxylative fluorination of the general aliphatic carboxylic acids with Selectfluor as a strong electrophilic reagent (Scheme 1). In this work, we reported that organic photocatalysts, such as 9-mesityl-10-methylacridinium perchlorate or Riboflavin, [10,11] are able to efficiently promote the decarboxylative fluorination of aliphatic carboxylic acids affording monofluoroalkanes, aryl monofluoromethyl ethers or fluoroesters in good to excellent yields.…”

“…And yet, the reaction catalyzed by less oxidizing Ru(bpy)3Cl2 almost did not provide fluorination product (Table 1, entry 2). [9] The Riboflavin, Eosin Y and Rhodamine B were also tested, but only Riboflavin gave a positive result (Table 1, entries [3][4][5]. The base also affected this transformation Having established effective conditions for decarboxylative fluorination, we next evaluated the scope of aliphatic carboxylic acids and the generality of this protocol.…”

Photoredox radical conjugate addition of dithiane-2-carboxylate promoted by an iridium(iii) phenyl-tetrazole complex: a formal radical methylation of Michael acceptors

“…9 Furthermore, the generation of primary radicals under photocatalytic conditions after extrusion of CO 2 is challenging, and just one example where primary radicals are intercepted by fluorinating agents is reported in the literature. 10 However, to the best of our knowledge, the generation and reaction of primary radicals is still an open issue in photocatalytic Michael reactions. Furthermore, addition of methyl radicals, recently reported using an ambitious methodology based on a Minisci type reaction, 11,12 has still not been developed in the area of photocatalysis.…”