Palladium-catalyzed decarboxylative ortho-amidation of O-methyl ketoximes with oxamic acids

Synthesis of amide-functionalized isoquinoline derivatives by photo-induced carbamoyl radical cascade amidation/cyclization

Isoquinoline-1,3-dione derivatives are of paramount importance in pharmaceutical research due to their versatile bioactivities, including notable anti-tumor and antibacterial properties. This study developed a novel method to synthesize amide-functionalized isoquinoline derivatives by a cascade amidation/cyclization of N-(methacryloyl)benzamide with the carybamonyl radical, generated from oxamic acids with the organic photosensitizer 4CzIPN. Mechanistic investigations, supported by radical scavenger experiments and HRMS analysis, unequivocally established a radical-mediated reaction pathway, with control studies validating the proposed cyclization cascade. This protocol offers distinct advantages including mild reaction conditions, environmental benignity, and broad substrate scope for the synthesis of amide-functionalized isoquinoline-1,3-diones. Furthermore, this synthetic platform has been successfully extended to the synthesis of amide-functionalized oxindoles and succinimides bearing α-quaternary carbon centers, underscoring its broad synthetic utility.

Advances in transition-metal catalyzed C-H bond activation of amidines to synthesize aza-heterocycles

Amidine compounds, as important nitrogen analogues of isoelectronic carboxylic acids, are found throughout biologically active molecules and serve as the most attractive precursors for the synthesis of N-containing compounds. In this review, the advancements in the synthesis of aza-heterocycles via transition-metal catalyzed C-H bond activation of amidines have been summarized through diverse annulation reactions. Amidines act as two-electron donors via the more basic and less sterically crowded imino lone pair and coordinate with transition-metals, in which N-H imine could act as both directing group and intramolecular nucleophile, electrophile or proton acceptor. The mechanisms of different annulation pathways will be highlighted in this review along with a discussion of more recent developments in the field.

Silver-Catalyzed Decarboxylative Coupling of Oxamic Acids with Styrenes to Synthesize E-Cinnamamides: A Distinguish Reaction Pathway

A silver-catalyzed decarboxylative coupling of oxamic acids with styrenes has been developed to produce E-cinnamamides. Oxamic acids act as efficient precursors for carbamoy radicals. Based on the mechanistic experiments and intermediate analysis, the proposed mechanism involves radical addition to styrenes, followed by oxidation and solvent participation, ultimately leading to the formation of cinnamamides which is different from the reported cases.

Design, synthesis, and exploration of antibacterial activity of 6H-1,2-oxazin-6-ones

This study reports the in silico design of 30 6H-1,2-oxazin-6-ones against DHFR and PTC antimicrobial targets. Docking compounds 1, 3, 4, 6, and 8 with both enzymes was favorable, outperforming Trimethoprim with DHFR. Therefore, 12 6H-1,2-oxazin-6-ones, including the most promising compounds, were synthesized through an aminolysis reaction of β-cyanoketones with hydroxylamine hydrochloride, obtaining moderate to high yields (55-88%). Subsequently, antibacterial studies were conducted against five bacteria: four Gram-positive MRSA (ATCC 43300 and three clinical isolates) and one Gram-negative (E. coli ATCC 25922). Compounds 1, 2, 3, 4, 6, and 8 inhibited bacterial growth with MIC values ranging from 3.125 to 200 μg mL-1. Compound 1 showed better activity against Gram-positive bacteria than Linezolid. Toxicity assays indicated no adverse effects of the active oxazinones in silico and in vitro. This study demonstrated the antibacterial potential of the selected 6H-1,2-oxazin-6-ones against resistant human pathogenic bacteria.

Metal-free synthesis of carbamoylated dihydroquinolinones via cascade radical annulation of cinnamamides with oxamic acids

We report a metal-free procedure for the sustainable synthesis of carbamoylated dihydroquinolinones via tandem addition-cyclization of carbamoyl radicals to cinnamamides. Readily accessible, non-toxic and inexpensive oxamic acids are used as carbamoyl radical precursors. This highly straightforward method provides a mild and environmentally friendly route showing good atom economy and excellent functional group tolerance to obtain diverse medicinally important carbamoylated dihydroquinolinones in one pot. The cascade cyclization is also modular and step-economical with a wide substrate scope and the products were obtained in good to excellent yields. Additionally, the tolerance to air and water, operational simplicity, low cost and scalability enhance the practical value of the proposed synthetic strategy. Preliminary mechanistic studies reveal that cheap and environment-friendly ammonium persulfate acts as a radical initiator in the cascade process and generates carbamoyl radicals from oxamic acids. The synthetic utility of this method is further demonstrated by late stage functionalization of drug molecules with good yields.

Oxamic acids: useful precursors of carbamoyl radicals

This review article describes the recent development in the chemistry of carbamoyl radicals generated from oxamic acids. This mild and efficient method compares well with previous methods of generation of these nucleophilic radicals. The oxidative decarboxylation of oxamic acids can be mediated through thermal, photochemical, electrochemical or photoelectrochemical means, generating carbamoyl radicals, which may further add to unsaturated systems to provide a broad range of important amides. Oxidative decarboxylation of oxamic acids also offers a straightforward entry for the preparation of urethanes, ureas, and thioureas.

Direct C-H Functionalization of Phenanthrolines: Metal- and Light-Free Dicarbamoylations

A direct method for C-H dicarbamoylations of phenanthrolines has been developed, which is capable of directly installing primary, secondary as well as tertiary amides. This is a significant improvement on the previous direct method, which was limited to primary amides. The metal-, light-, and catalyst-free Minisci-type reaction is cheap, operationally simple, and scalable. We demonstrate that the step efficiency toward dicarbamoylated phenanthroline targets can now be significantly improved.

The construction of benzimidazo[2,1-a]isoquinolin-6(5H)-ones from N-methacryloyl-2-phenylbenzoimidazoles through radical strategies

Benzimidazo[2,1-a]isoquinolin-6(5H)-one constitutes a structurally unique class of tetracyclic N-heterocycles that are found throughout a myriad of biologically active natural products, pharmaceutical compounds, and functional materials. Various synthetic routes for the preparation of benzimidazo[2,1-a]isoquinolin-6(5H)-ones have been reported. In particular, the use of N-methacryloyl-2-phenylbenzoimidazoles to construct benzimidazo[2,1-a]isoquinolin-6(5H)-ones through various radical strategies have attracted widespread attention due to the versatility and simple preparation of raw materials, as well as the step-economy and mild reaction conditions. Using representative examples, we highlight significant progress in the synthesis of benzimidazo[2,1-a]isoquinolin-6(5H)-ones, including the selection of the catalytic system, substrate scope, mechanistic understanding, and applications. The contents of this review focus on the development of C-, S-, P-, and Si-centered radical addition-intramolecular cyclization strategies.

Facile synthesis of carbamoylated benzimidazo[2,1-a]isoquinolin-6(5H)-ones via radical cascade cyclization under metal-free conditions

A highly efficient synthesis of carbamoylated benzimidazo[2,1-a]isoquinolin-6(5H)-ones using 2-arylbenzoimidazoles and oxamic acids was developed. This strategy tolerated various substrates as the starting materials to generate the corresponding products in good yields under metal-free conditions.

Isoindolinone Synthesis via One-Pot Type Transition Metal Catalyzed C-C Bond Forming Reactions

Isoindolinone structure is an important privileged scaffold found in a large variety of naturally occurring as well as synthetic, biologically and pharmaceutically active compounds. Owing to its crucial role in a number of applications, the synthetic methodologies for accessing this heterocyclic skeleton have received significant attention during the past decade. In general, the synthetic strategies can be divided into two categories: First, direct utilization of phthalimides or phthalimidines as starting materials for the synthesis of isoindolinones; and second, construction of the lactam and/or aromatic rings by different catalytic methods, including C-H activation, cross-coupling, carbonylation, condensation, addition and formal cycloaddition reactions. Especially in the last mentioned, utilization of transition metal catalysts provides access to a broad range of substituted isoindolinones. Herein, the recent advances (2010-2020) in transition metal catalyzed synthetic methodologies via formation of new C-C bonds for isoindolinones are reviewed.

Rhodium-catalyzed ortho-acrylation of aryl ketone O-methyl oximes with cyclopropenones

An efficient Rh-catalyzed ortho-acrylation reaction for the synthesis of chalcones from O-methyl ketoximes and cyclopropenones via C-H bond activation has been described. This cross-coupling reaction exhibits high functional group tolerance and regioselectivity. A wide range of chalcone derivatives are obtained in moderate to good yields under mild conditions.