Unified Approach to Diverse Heterocyclic Synthesis: Organo-Photocatalyzed Carboacylation of Alkenes and Alkynes from Feedstock Aldehydes and Alcohols

We report an organo-photocatalyzed carboacylation reaction that offers a springboard to create chemical complexity in a diversity-driven approach. The modular one-pot method uses feedstock aldehydes and alcohols as acyl surrogates and commercially available Eosin Y as the photoredox catalyst, making it simple and affordable to introduce structural diversity. Several biologically relevant skeletons have been easily synthesized under mild conditions in the presence of visible light irradiation by fostering a radical acylation/cyclization cascade. The proposed reaction mechanism was further illuminated by a number of spectroscopic studies. Furthermore, we applied this protocol for the late-stage functionalization of pharmaceuticals and blockbuster drugs.

Palladium-Catalyzed Carbonylative Hiyama-Denmark Reaction toward the Synthesis of Aryl Carbonyl-Containing Oxindoles

A palladium-catalyzed domino Heck cyclization/carbonylative Hiyama-Denmark cross-coupling reaction between alkene-tethered aryl iodides and silylcarboxylic acids is presented. This reaction proceeds well without toxic carbon monoxide (CO) gas and has good functional group tolerance, providing an alternative access to carbonyl-containing oxindoles. In this transformation, silylcarboxylic acids play a dual role as a CO source and a nucleophile.

Desulfonylation via Radical Process: Recent Developments in Organic Synthesis

As the "chemical chameleon", sulfonyl-containing compounds and their variants have been merged with various types of reactions for the efficient construction of diverse molecular architectures by taking advantage of their incredible reactive flexibility. Currently, their involvement in radical transformations, in which the sulfonyl group typically acts as a leaving group via selective C-S, N-S, O-S, S-S, and Se-S bond cleavage/functionalization, has facilitated new bond formation strategies which are complementary to classical two-electron cross-couplings via organometallic or ionic intermediates. Considering the great influence and synthetic potential of these novel avenues, we summarize recent advances in this rapidly expanding area by discussing the reaction designs, substrate scopes, mechanistic studies, and their limitations, outlining the state-of-the-art processes involved in radical-mediated desulfonylation and related transformations. With a specific emphasis on their synthetic applications, we believe this review will be useful for medicinal and synthetic organic chemists who are interested in radical chemistry and radical-mediated desulfonylation in particular.

Metal-free oxidative acylation/cyclization of N-methacryloyl-2-phenylbenzoimidazole with aryl aldehydes: an easy access to benzimidazo[2,1-a]isoquinolin-6(5H)-ones

A metal-free radical cyclization strategy has been developed for the synthesis of fused benzimidazo[2,1-a]isoquinolin-6(5H)-one derivatives using 70% tert-butylhydroperoxide in water (TBHP).

Photocatalytic acylarylation of unactivated alkenes with diaryliodonium salts toward indanones and related compounds

A photocatalytic acylarylation of unactivated alkenes using diaryliodonium salts is described, giving 2-benzyl indanones and related compounds in promising yields with excellent diastereoselectivity.

A chemoselective and continuous synthesis of m-sulfamoylbenzamide analogues

For the synthesis of m-sulfamoylbenzamide analogues, small molecules which are known for their bioactivity, a chemoselective procedure has been developed starting from m-(chlorosulfonyl)benzoyl chloride. Although a chemoselective process in batch was already reported, a continuous-flow process reveals an increased selectivity at higher temperatures and without catalysts. In total, 15 analogues were synthesized, using similar conditions, with yields ranging between 65 and 99%. This is the first automated and chemoselective synthesis of m-sulfamoylbenzamide analogues.

Photocatalyst-free hypervalent iodine reagent catalyzed decarboxylative acylarylation of acrylamides with α-oxocarboxylic acids driven by visible-light irradiation

A hypervalent iodine(iii) reagent catalyzed carbonylarylation of acrylamides with α-oxocarboxylic acids driven by visible-light without a photoredox catalyst has been developed. The reactions generate the corresponding products in good yields at room temperature. Experiments indicate that a blue LED (450-455 nm) is the most effective energy for the cleavage of the oxygen-iodine bond to initiate the reaction. Mechanistic studies further demonstrate that the reaction undergoes a cascade decarboxylative radical addition/cyclization process along with releasing CO2 and H2.

Visible-Light-Mediated Photocatalytic Difunctionalization of Olefins by Radical Acylarylation and Tandem Acylation/Semipinacol Rearrangement

A novel method for the mild photoredox-mediated tandem radical acylarylation and tandem acylation/semipinacol rearrangement has been developed. The synthesis of highly functionalized ketones bearing all-carbon α- or β-quaternary centers has been achieved using easily available symmetric aromatic carboxylic anhydrides as the acyl radical source. The method allows for a straightforward introduction of the keto functionality and concomitant construction of molecular complexity in a single operation.

Visible light-promoted synthesis of 4-(sulfonylmethyl)isoquinoline-1,3(2H,4H)-diones via a tandem radical cyclization and sulfonylation reaction

4-(Sulfonylmethyl)isoquinoline-1,3(2H,4H)-diones were synthesized via a visible-light-promoted cyclization and sulfonylation reaction catalyzed by fac-Ir(ppy)₃.

Acyl Radicals from Aromatic Carboxylic Acids by Means of Visible-Light Photoredox Catalysis

Simple and abundant carboxylic acids have been used as acyl radical precursor by means of visible-light photoredox catalysis. By the transient generation of a reactive anhydride intermediate, this redox-neutral approach offers a mild and rapid entry to high-value heterocyclic compounds without the need of UV irradiation, high temperature, high CO pressure, tin reagents, or peroxides.

Metal-free direct cyanoisopropylation/arylation of N-arylacrylamides or N-alkyl-N-(arylsulfonyl)acrylamides with AIBN: a simple and mild approach to cyano-containing oxindoles

A general, highly efficient approach to cyano-containing oxindoles is presented that is achieved by a metal-free direct cyanoisopropylation/arylation ofN-arylacrylamides orN-alkyl-N-(arylsulfonyl)acrylamides with AIBN.