Decarboxylative Acetoxylation of Aliphatic Carboxylic Acids

Silver-Catalyzed Decarboxylative Nitrooxylation of Aliphatic Carboxylic Acids

Here, we present a silver-catalyzed decarboxylative nitrooxylation via a radical-based approach. The substrate scope of this reaction prototype extends to nonactivated primary and secondary carboxylic acids. This protocol provides a practical method for the synthesis of an unprecedented family of organic nitrates and exhibits wide functional group compatibility. Preliminary mechanistic studies reveal that a high-valent silver(II) nitrate complex is a versatile NO3 resource pool, allowing for facile C-O bond formation.

Transition metal-free decarboxylative olefination of carboxylic acid salts

The cost-effective and efficient synthesis of alkenes is highly significant due to their extensive applications in both synthetic and polymer industries. A transition metal-free approach has been devised for the chemoselective olefination of carboxylic acid salts. This modular approach provides direct access to valuable electron-deficient styrenes in moderate to good yields. Detailed mechanistic studies suggest anionic decarboxylation is followed by halogen ion transfer. This halogen transfer leads to an umpolung of reactant electronics, allowing for a rate-limiting rebound elimination.

Cu(II) salts as terminal oxidants in visible-light photochemical oxidation reactions

Photochemistry provides an important platform for the discovery of synthetically useful transformations. The development of new oxidative photoreactions, however, has proven to be relatively challenging. The importance of the identity of the terminal oxidant has been an underappreciated consideration in the design of these reactions. Many of the most common terminal oxidants used in ground-state catalytic methods are poorly compatible with the one-electron oxidation state changes characteristic of photoredox reactions and result in hard-to-control deleterious side reactions. As an alternative, Cu(II) salts have emerged as versatile terminal oxidants in photochemical oxidation reactions that are terrestrially abundant, cost-effective, and readily compatible with one-electron oxidation state changes. This review highlights recent reaction methods that leverage Cu(II) oxidation in combination with the photochemical activation of substrates or that use Cu(II) salts as both the active chromophore and terminal oxidant.

Single-Step Synthesis of γ-Ketoacids through a Photoredox-Catalyzed Dual Decarboxylative Coupling of α-Oxo Acids and Maleic Anhydrides

A photocatalytic methodology for the single step synthesis of γ-ketoacids from α-ketoacids has been developed. This method employs maleic anhydrides as traceless synthetic equivalents of acrylic acids, achieving a selective cross-coupling via a dual decarboxylative strategy, where molecular CO2 is released as the only waste byproduct. The method has also been expanded to incorporate a highly regioselective, 3-component coupling with various alcohols to access functionalized γ-ketoesters.

Visible-Light-Mediated Three-Component Decarboxylative Coupling Reactions to Synthesize 1,4-Diol Monoethers

An efficient approach for 1,2-difunctionalization of aromatic olefins and the synthesis of functionalized 1,4-diols monoethers has been established via a photoinduced three-component reaction of an α-alkoxycarboxylic acid, an aromatic olefin, and an aldehyde. The reaction proceeds by photoinduced oxidative decarboxylation of the carboxylic acid followed by the addition of the α-alkoxyalkyl radical to the olefin, one-electron reduction of the addition radical, and the nucleophilic attack of the resulting carbanion to the aldehyde. Besides the convenient one-pot protocol of the three-component reaction, this method offers several other advantages, including good functional group tolerance for the three substrates, gentle reaction conditions, and ease of scaling up. The reaction mechanism has been investigated through free radical trapping experiment and isotope labeling experiments.

Allylic Amination of Highly Substituted Alkenes Enabled by Photoredox Catalysis and Cu(II)-Mediated Radical-Polar Crossover

Allylic amination reactions enable the conversion of alkene feedstocks into value-added products with significant synthetic versatility. Here we describe a method for allylic amination involving photoredox activation and Cu(II)-mediated radical-polar crossover. A range of structurally varied allylic amines can be accessed using this strategy. The regioselectivity of this process is complementary to those of conventional methods for allylic amination.

Redox Inversion: A Radical Analogue of Umpolung Reactivity for Base- and Metal-Free Catalytic C(sp3)-C(sp3) Coupling

The construction of alkyl-alkyl bonds is a powerful tool in organic synthesis. Redox inversion, defined as switching the donor/acceptor profile of a functional group to its acceptor/donor profile, is used for C(sp³)-C(sp³) coupling. We report a photocatalytic coupling of carboxylic acids to form bibenzyls through a radical-radical coupling. Mechanistic insight is gained through control reactions. This unexplored redox-opposite relationship between a carboxylic acid and its redox-active ester is implemented in catalysis.

Copper-Catalyzed Decarboxylative Elimination of Carboxylic Acids to Styrenes

A copper-catalyzed decarboxylative elimination reaction of (hetero)aromatic propionic acids to vinyl (hetero)arenes has been developed. This method furnishes alkenes from carboxylic acids without the need for stochiometric Pb or Ag additives or expensive or specialized photocatalysts. A series of mechanistic experiments indicate that the reaction proceeds via benzylic deprotonation and subsequent radical decarboxylation; a pathway that is distinct from the single-electron-transfer mechanisms implicated in related decarboxylative elimination reactions.

Synthesis of Benzylic Alcohols by Decarboxylative Hydroxylation

Herein, we demonstrate an efficient method for the decarboxylative hydroxylation of carboxylic acids with silver(I) as the catalyst and cerium ammonium nitrate as the oxidant and its utility in chemoselective late-stage functionalization of natural products and drug molecules. The chemoselectivity of this protocol arises from a benzylic nitrate intermediate that retards further oxidation and is hydrolyzed to the final benzylic alcohol product. Mechanistic investigation reveals that the facile oxidation of silver carboxylate affords silver(II) species as an intermediate oxidant responsible for decarboxylation.

Cu-Photoredox-catalyzed C(sp)-C(sp3) coupling of redox-active esters with terminal alkynes

Visible-light-induced C(sp)-C(sp3) coupling of redox-active esters with terminal alkynes has been developed. The activation of carboxylic acids as their redox-active ester derivatives was important for this decarboxylative alkynylation. The strategy established here facilitates the straightforward introduction of triple-bonded functional groups and avoids additional photocatalysts. A wide range of primary, secondary and tertiary acids can be converted into the target products; so this reaction exhibits a broad substrate scope and tolerance of functional groups. Mechanistic experiments suggested that this reaction may undergo a radical process. Under mild reaction conditions, a copper acetylide ligand as a photocatalyst delivered an electron to redox-active ester derivatives, and generated alkyl radicals. The radicals reacted with Cu(ii) to deliver a Cu(iii) complex, and then reductive elimination gave the products.

Photophysical properties and electron transfer photochemical reactivity of substituted phthalimides

Substituents on phthalimide affect its photophysics and photochemical reactivity. Electron donors generally result in low quantum yields of intersystem crossing and reactivity from singlet excited states.