Radical-Mediated Decarboxylative C–C and C–S Couplings of Carboxylic Acids via Iron Photocatalysis

Abstract

Despite the significant success of decarboxylative radical reactions, the catalytic systems vary considerably upon different radical acceptors, requiring renewed case-by-case reaction optimization. Herein, we developed an iron catalytic condition that enables the highly efficient decarboxylation of various carboxylic acids for a range of radical transformations. This operationally simple protocol was amenable to a wide array of radical acceptors, delivering structurally diverse oxime ethers, alkenylation, alkynylation, thiolation, and amidation products in useful to excellent yields (>40 examples, up to 95% yield).

Light-induced ligand-to-metal charge transfer of Fe(iii)-OR species in organic synthesis

“…In 2024, Hu and Wei reported several decarboxylation couplings to construct C–C and C–S bonds (Scheme 10), 17 in which the alkyl radical generated from the light-induced iron-catalyzed decarboxylation could be trapped by various radical acceptors. Using 390 nm LEDs as the light source, the reaction provided multiple products of alkenylation, alkynylation, thiolation and amidation, including oxime ethers in the presence of 10 mol% of Fe(NO 3 ) 3 ·9H 2 O, 10 mol% of di(2-picolyl)-amine and 2 equivalents of Na 2 CO 3 .…”

“…Over the last five years, LMCT of iron species has been developed substantially and applied to different kinds of organic transformations. 1 f ,6–30 These studies are mainly based on LMCT of Fe( iii )-Cl and Fe( iii )-OR species. A chloride radical, which is a well-known hydrogen atom transfer (HAT) agent, can be produced in LMCT of Fe( iii )-Cl species.…”

Aminomethylations of electron-deficient compounds—bringing iron photoredox catalysis into play

“…While Cu( i ) complexes have been used as a more Earth-abundant alternative in photoredox catalysis, 32–37 and photosensitisers based on Mn( i ), 38 Cr(0) and Cr( iii ), 39–42 Co( iii ), 43 Mo(0) 44 are on the rise, photoredox catalysts based on iron nevertheless remain attractive candidates and dissociative inner-sphere SET upon ligand-to-metal charge transfer (LMCT) excitation of Fe( iii ) currently also receives much attention for its applications in photoredox catalysis. 45–50 However, so far there are only very few examples of synthetic transformations driven by outer-sphere charge transfer (CT) of iron-based photosensitisers. 48,51…”

Iron-Catalyzed Photochemical Synthesis of Sulfinamides from Aliphatic Hydrocarbons and Sulfinylamines

“…Within this paradigm, the direct excitation of high-valent metal–ligand complexes enables the generation of halogen radical species to initiate intermolecular hydrogen atom transfer (HAT) processes with hydrocarbons and trigger a series of coupling reactions of C­(sp 3 )–H bonds . Recently, we developed a radical phosphorylation of aliphatic C–H bonds and decarboxylative functionalization of carboxylic acids via photoinduced LMCT strategy . Prompted by these achievements, we recently sought to devise a new and direct sulfinamidation technology that allows the rapid synthesis of high-value-added sulfinamides from simple hydrocarbons and N -sulfinylamines via an iron-catalyzed photochemical LMCT strategy (Scheme c) and also provides convenient access to highly functionalized sulfur­(VI) derivatives, such as sulfonimidate esters, sulfonimidamides, and sulfonamides.…”