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

Abstract

In the quest for sustainable processes, the selection of resources and catalysts is of central importance. Carboxylic acids, which are abundant, stable and ideally biobased feedstocks, can be considered as attractive platforms towards a range of functionalized molecules. A recent resurgence of photoinduced ligand‐to‐metal charge transfer (LMCT) of carboxylates led to tremendous developments in the field of earth‐abundant metal mediated, visible‐light induced (non)‐decarboxylative transformations of carboxylic acids. These reactions combine the use of available starting materials, low‐consuming energy source and abundant catalysts. Besides these undeniable advantages, they also provide mild, highly selective and innovative conditions towards complex molecule functionalization. The objective of this review is to give an overview of the recent advances in LMCT of carboxylates with a special focus on mechanistic aspects of these transformations.

Photocatalytic decarboxylative selenocyanation of 2-aryloxy and 2-aryl carboxylic acids with N-selenocyanatophthalimide

“…These results indicated that the aryloxy group is an essential structural moiety and single-electron oxidation occurs on the oxygen atoms of the aryloxy group rather than on those of the carboxyl group, which is different from the general decarboxylative functionalization reaction involving the generation of a carboxyl radical in the presence of bases. 14 Moreover, the enantiopure ( S )-ibuprofen ( 4m ) provided a racemic selenocyanato product 5m (Scheme 3e).…”

“…Nitromethane, dichloromethane, toluene and hexafluoroisopropanol (HFIP) were less effective (entries 11, 12, 18 and 19). In acetone, THF, 1,4-dioxane and DMSO, the reaction shut down (entries [14][15][16][17]. Changing the wavelength of visible light was not helpful to this reaction (entries 20 and 21).…”

Photoelectrochemical Cerium Catalysis via Ligand-to-Metal Charge Transfer: A Rising Frontier in Sustainable Organic Synthesis

“…Unlike the photo-excited Ce(III) complexes, the Ce(IV) ones rarely display luminescent properties but often undergo LMCT, resulting in the single electron oxidation of the ligands and reduction of the Ce(IV) to Ce(III). 9 Accordingly, the LMCT of Ce(IV) complexes has already been long applied to LMCT in inorganic chemistry. In 2017, the Anwander group found the LMCT bands of several Ce(IV)-alkoxide complexes in the UV-visible spectra (Figure 3a).…”

“…As a representative of intramolecular redox, LMCT (Scheme 6c ) has been long applied in organic photochemical synthesis. 9 19 Perhaps due to lack of knowledge of the electrochemical properties of metal-centered photocatalysts, photoelectrochemical examples are rarely explored. Therefore, the rise of dPEC strategy lies in the exploration of photoelectrochemical metal catalysts.…”

Photoinduced Copper-Promoted Decarboxylative Trifluoromethylselenolation of Aromatic Carboxylic Acids with [Me4N][SeCF3]

“…Approaches for the direct formation of carbon–carbon and carbon–heteroatom bonds by decarboxylative functionalization of carboxylic acids have been well established . Since the thermal decarboxylation often required high temperatures, harsh reagents, activating groups, and/or conditions that may destroy the subsequent transformations, the photocatalytic decarboxylative functionalization of carboxylic acids or their redox-active esters has emerged as the more attractive strategy for the construction of the target compounds in recent years . In particular, the photoinduced decarboxylative fluoroalkylation of carboxylic acids with the appropriate F-reagents has become a general and powerful tool for the synthesis of fluoroalkylated molecules .…”