Visible-Light-Induced Decarboxylative Fluorination of Aliphatic Carboxylic Acids Catalyzed by Iron

Abstract

An efficient and inexpensive protocol for the direct decarboxylative fluorination of aliphatic carboxylic acids catalyzed with iron salts under visible light is presented. This new method allows the facile fluorination of a diverse array of carboxylic acids even on gram scale using a Schlenk flask without loss of efficiency. Mechanistic studies suggest that the photoinduced ligand-to-metal charge transfer process enables the generation of the key step to generate the carboxyl radical intermediates.

Visible light-mediated halogenation of organic compounds

“…A cheaper non-noble iron catalyst was recently used for decarboxylative fluorination, based on an LMCT mechanism (Scheme 18). 47 This transformation was applicable for aliphatic acids 29 only. Scheme 17 General decarboxylative halogenation approach.…”

Photoinduced Ligand‐to‐Metal Charge Transfer of Carboxylates: Decarboxylative Functionalizations, Lactonizations, and Rearrangements

“…While the formation of C−C, C−O or C−N bonds from radicals issued from decarboxylation is well documented, examples of C−X bonds formation are much scarcer. Very recently, an iron‐catalyzed decarboxylative fluorination of aliphatic carboxylic acids was disclosed [59] . The authors reasoned that a radical issued from a decarboxylation step could be scavenged by a fluoride radical donor to furnish the desired product.…”

“…Very recently, an iron-catalyzed decarboxylative fluorination of aliphatic carboxylic acids was disclosed. [59] The authors reasoned that a radical issued from a decarboxylation step could be scavenged by a fluoride radical donor to furnish the desired product. 1-Tosylpiperidine-4-carboxylic acid was chosen as the model substrate and an extensive optimization process was conducted, including the screening of iron salts, ligands, bases, fluorine donor and light wavelength.…”

Ferrocenophanium Stability and Catalysis

“…Accordingly, several organic transformations have been reported to be catalyzed by iron-based catalyst systems, such as oxidations, reductions, substitutions, cross-coupling, or polymerization reactions. Iron-based catalysts can range from simple salts like FeX 2 or FeX 3 [ 18 , 19 , 20 ], Fe(OTf) 2 [ 21 , 22 ], Fe(OAc) 2 [ 23 , 24 , 25 , 26 ], or Fe(acac) 3 (acac = acetylacetonato) [ 27 ] to higher-sophisticated metal complexes such as Knölker’s or related complexes [ 28 , 29 ], iron complexes derived from phosphorus- [ 7 , 30 ] or nitrogen-coordinating ligands [ 31 , 32 ] or iron coordination compounds which can catalyze reactions site- or substrate-selectively [ 33 , 34 , 35 ] and enantioselectively [ 36 , 37 , 38 ].…”