Cobalt Homeostatic Catalysis for Coupling of Enaminones and Oxadiazolones to Quinazolinones

Recent advances in site-selective transformations of β-enaminones via transition-metal-catalyzed C-H functionalization/annulation

β-Enaminone transformation strategies are widely employed in the synthesis of numerous biologically active drugs and natural products, highlighting their significance in medicinal chemistry. In recent years, various strategies have been developed for synthesizing several five- and six-membered heterocycles, as well as substituted polyaromatic scaffolds, which serve as crucial synthons in drug development, from β-enaminones. Among these approaches, site-selective transformations of β-enaminones via C-H activation and annulation have been particularly well explored. This review summarizes the most recent literature (over the past eight years) on β-enaminone transformations for developing bioactive scaffolds through site-selective C-H bond functionalization and annulation.

Oxadiazolone-Based Aromatic Annulations: A Nitrenoid Precursor for Tricyclic Aminoheterocycles

Nitrogen-containing heterocycles are present in most approved drugs, reflecting the significance of their synthetic strategies. By utilizing oxadiazolone as a nitrenoid (nitrene-like) precursor, we have developed a general strategy for the annulation with nucleophilic heterocycles to access various polycyclic aminoheterocycles. We have discovered that 2-pyrryl-substituted substrates undergo a rearrangement, which indicates a spirocyclization-migration pathway. Given their fluorescence and biological activity as kinase hinge binders, these fragment-like aminoheterocycles represent potential starting points for applications in chemical biology and drug discovery.

I2-Promoted Chemoselective Annulative Coupling of 2-Aminobenzamides with Sulfoxonium Ylides: Easy Access to Quinazolinones

A flexible and metal-free synthetic approach for synthesizing 2-benzoyl quinazolinones and 2-aryl quinazolinones via molecular iodine-mediated annulative coupling of sulfoxonium ylides with 2-aminobenzamides has been disclosed. The method demonstrates remarkable chemoselectivity and efficiency, leading to high yields of 2-benzoyl quinazolinones and 2-aryl quinazolinones under optimized conditions. The broad substrate scope, scalability, and practical utility were highlighted through diverse applications, including gram-scale reactions and the synthesis of biologically significant compounds such as tryptanthrin and the chemo/biosensor derivative.

Tf2O-Mediated Tandem Reaction of Enaminones for the Synthesis of Functionalized Conjugated-Enals/β-Naphthalaldehydes

A highly efficient and regioselective method for constructing functionalized conjugated enals via the Tf2O-mediated tandem reaction of enaminones with thiophenols has been described. Chain products with excellent stereoselectivity could be obtained through substrate regulation. Additionally, a feasible method for synthesizing β-naphthalaldehydes through PhSO2Na/DABCO promoting hydrogen atom transfer process has also been reported here. Mechanism studies have shown that 2-formyl vinyl triflate 8 and sulfonylated enal 9 were the key intermediates in this process.

A Direct Method for Synthesis of Quinoxalines and Quinazolinones Using Epoxides as Alkyl Precursor

An iodine-mediated one-pot synthesis of pyrrolo/indolo [1,2-a]quinoxalines and quinazolin-4-one via utilizing epoxides as alkyl precursors under metal-free conditions has been described. Both 1-(2-aminophenyl)-pyrrole and 2-aminobenzamide could be applied to this protocol. A total of 33 desired products were obtained with moderate to good yields. This methodology was suitable for wide-scale preparation and the obtained products could be further modified into promising pharmaceutically active reagents.

Catalytic Olefin-Imine Metathesis: Cobalt-Enabled Amidine Olefination with Enaminones

Organic metathesis reactions allow for expedient assembly of diverse molecular skeletons and appendages through the exchange of molecular fragments. The olefin-imine variant of this process, in particular, can expand the synthetic toolbox for manipulating carbon-carbon and carbon-nitrogen bonds but has thus far been achieved only on a stoichiometric metal-mediated basis. Herein, we report the development of a catalytic olefin-imine metathesis reaction, featuring cobalt-catalyzed amidine olefination with enaminones and a versatile product synthon enabling further structural diversification.