Pd(II)-Catalyzed Fujiwara-Moritani Reactions for the Synthesis and Functionalization of Substituted Coumarins

An Improved Gold(I) Catalytic System for the Preparation of Coumarins via Intramolecular Cyclization

A catalytic system comprising a gold(I) complex with an N-heterocyclic carbene (NHC) ligand in an ionic liquid as solvent exhibits higher catalytic efficiency compared to state of the art systems in the title reaction, which enables using down to 0.01 mol % gold. A commercial gold(I) catalyst such as IPrAuNTf2 can be employed for this purpose. In the case of less reactive substrates bearing electron-withdrawing substituents at the phenol moiety, a tailor made NHC-gold(I) precatalyst exhibits improved reactivity and can be advantageously employed compared to the commercial one.

Syntheses, reactivity, and biological applications of coumarins

This comprehensive review, covering 2021-2023, explores the multifaceted chemical and pharmacological potential of coumarins, emphasizing their significance as versatile natural derivatives in medicinal chemistry. The synthesis and functionalization of coumarins have advanced with innovative strategies. This enabled the incorporation of diverse functional fragments or the construction of supplementary cyclic architectures, thereby the biological and physico-chemical properties of the compounds obtained were enhanced. The unique chemical structure of coumarine facilitates binding to various targets through hydrophobic interactions pi-stacking, hydrogen bonding, and dipole-dipole interactions. Therefore, this important scaffold exhibits promising applications in uncountable fields of medicinal chemistry (e.g., neurodegenerative diseases, cancer, inflammation).

Pd@GO catalyzed stereo- and regio-selective addition of arenes to alkynes and synthesis of coumarins via C-H functionalization

A stereo- and regio-selective addition of arenes to alkynes via C-H bond functionalization has been developed using palladium nanoparticles supported on graphite oxide (Pd@GO) as the reusable catalyst. The prepared catalyst was characterized by various spectroscopic techniques such as FT-IR, TEM, SEM, EDX, P-XRD, and XPS analysis. The thermal stability of the catalyst was established by TGA. The C-H functionalized products were obtained in good to excellent yields (69-92%) at room temperature. The methodology further extended to the synthesis of biologically and pharmaceutically important coumarin molecules from phenols and alkynes. Good to excellent yields of the coumarins (74-92%) were obtained. After the reaction, the catalyst was separated by centrifugation followed by filtration. The recovered catalyst was washed and reused up to five cycles. The advantages of this method are the simple procedure of the catalyst preparation, high catalytic efficiency, high selectivity, good functional group tolerance, low catalyst loading, and gram-scale synthesis.

Visible-Light-Induced Tandem Radical Brominative Addition/Cyclization of Activated Alkynes with CBr4 for the Synthesis of 3-Bromocoumarins

A visible-light-induced tandem radical brominative addition/spiro-cyclization/1,2-ester migration of activated alkynes with CBr₄ is developed. This protocol features good functional group tolerance, operational simplicity, and mild reaction conditions without the use of catalysts and external additives, providing easy access to valuable 3-bromocoumarins in generally high yields.

Coumarins Synthesis and Transformation via C–H Bond Activation—A Review

For several decades, coumarins have attracted considerable attention due to the fact of their application in diverse fields such as medical science and biomedical research as well as several industrial branches. Recently, many compounds containing the coumarin moiety have been intensively studied, mainly due to the fact of their biological activities such as antitumor, antioxidative, anti-HIV, vasorelaxant, antimicrobial, and anticancer. They are also widely used as fluorescent dyes and probes because of their great structural flexibility and large fluorescent quantum yields. For this reason, numerous attempts have been made to develop new and more practical methods for the synthesis of these compounds. This review aims at providing a comprehensive overview of coumarin synthesis methods by direct C–H bond activation in order to demonstrate the current state-of-the-art methods as well as the current limitations.