PhI(OAc)2/Pd(OAc)2 promoted the formation of 8-hydroxyquinoline derivatives from benzoxazoles and alcohols

A PhI(OAc)₂/Pd(OAc)₂ system that synergistically promotes the formation of 8-hydroxyquinoline derivatives from benzoxazoles and alcohols has been developed. The reaction proceeded smoothly with a range of benzoxazoles and alcohols to give the corresponding 8-hydroxyquinoline derivatives in moderate yields.

Reactions of α-Phenylglyoxylic Acids with ortho-Functionalized Anilines in Deep Eutectic Solvents: Selective Syntheses of 3-Aryl-2H-benzo[b][1,4]oxazin-2-ones, 2-Arylbenzothiazoles, and 3-Arylquinoxalin-2(1H)-ones

α-Phenylglyoxylic acid is a novel cyclization reagent. In this study, three cyclization products were synthesized by the reaction of α-phenylglyoxylic acids with ortho-functionalized anilines in deep eutectic solvents (DES). The five-membered-ring-formation products, the 2-arylbenzothiazoles, with a highest yield of 88%, were obtained by the reaction between 0.30 mmol of an o-aminothiophenol and 0.30 mmol of an α-phenylglyoxylic acid in choline chloride (ChCl)/d-(–)-tartaric acid DES at 60 °C for 0.5 h. The six-membered-ring-formation products, 3-aryl-2H-benzo[b][1,4]oxazin-2-one derivatives, were obtained in yields up to 99% by the reaction between 0.30 mmol of an o-aminophenol and 0.60 mmol of an α-phenylglyoxylic acid in ChCl/urea DES at 80 °C for 2.0 h. In the reaction between 0.30 mmol of o-phenylenediamine and 0.45 mmol of an α-phenylglyoxylic acid in ChCl/anhydrous tin(II) chloride DES at 70 °C for 1.5 h, the six-membered-ring-formation products, 3-arylquinoxalin-2(1H)-one derivatives, were synthesized, with a highest yield of 96%. This cyclization reaction occurred without the addition of other catalysts, and the title compounds were obtained with good yields under mild conditions.

α-Keto Acids as Triggers and Partners for the Synthesis of Quinazolinones, Quinoxalinones, Benzooxazinones, and Benzothiazoles in Water

A general and efficient method for the synthesis of quinazolinones, quinoxalinones, benzooxazinones, and benzothiazoles from the reactions of α-keto acids with 2-aminobenzamides, benzene-1,2-diamines, 2-aminophenols, and 2-aminobenzenethiols, respectively, is described. The reactions were conducted under catalyst-free conditions, using water as the sole solvent with no additive required, and successfully applied to the synthesis of sildenafil. More importantly, these reactions can be conducted on a mass scale, and the products can be easily purified through filtration and washing with ethanol (or crystallized).

Hypervalent Iodine(III)-Promoted Radical Oxidative C-H Annulation of Arylamines with α-Keto Acids

A novel catalyst-free radical oxidative C-H annulation reaction of arylamines with α-keto acids toward benzoxazin-2-ones synthesis under mild conditions was developed. This hypervalent iodine(III)-promoted process eliminated the use of a metal catalyst or additive with high levels of functional group tolerance. Hypervalent iodine(III) was both an oxidant and a radical initiator for this reaction. The synthetic utility of this method was confirmed by the synthesis of the natural product cephalandole A.

Ag(i)/persulfate-catalyzed decarboxylative coupling of α-oxocarboxylates with organotrifluoroborates in water under room temperature

The decarboxylative coupling of α-oxocarboxylates and organotrifluoroborates was carried out smoothly in water under room temperature. This novel and simple method is efficient, using AgNO₃/K₂S₂O₈ catalytic system to generate diarylketone products.

Direct α-heteroarylation of amides (α to nitrogen) and ethers through a benzaldehyde-mediated photoredox reaction

A photoredox reaction for cross-dehydrogenative coupling (CDC) was developed to Cα-arylate amides (α to nitrogen) and ethers using a variety of five- and six-membered electron-deficient heteroarenes. A unique decomposition mechanism of ammonium persulfate enhanced by photoexcited benzaldehydes was revealed. This benzaldehyde-mediated photoredox reaction proceeded smoothly with household 23 W CFL bulbs as the energy source under metal-free conditions, allowing the construction of new Csp2 -Csp2 and Csp3 -Csp2 bonds and access to important pharmacophores of broad utility using commercially available reagents.

Transition-metal free alkylarylation of acrylamides initiated by radical C–C bond cleavage of the tertiary cycloalkanols

An efficient Na₂S₂O₈-promoted radical cyclization reaction of acrylamides with the tertiary cycloalkanols has been developed. This one pot procedure involves a tandem C–C bond cleavage and two C–C bonds formation process.

Recent advances in catalytic decarboxylative acylation reactions via a radical process

This review highlights the recent advances in radical decarboxylative cross-coupling reactions of α-keto acids which provide powerful tools for C–C and C–X bond formations.