Biology-oriented synthesis of benzopyrano[3,4-c]pyrrolidines

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.

An Overview of the Synthesis of 3,4-Fused Pyrrolocoumarins of Biological Interest

3,4-Fused pyrrolocoumarins, synthetically prepared or naturally occurring, possess interesting biological properties. In this review, the synthetic strategies for the synthesis of the title compounds are presented along with their biological activities. Two routes are followed for that synthesis. In one, the pyrrole ring is formed from coumarin derivatives, such as aminocoumarins or other coumarins. In the other approach, the pyranone moiety is built from an existing pyrrole derivative or through the simultaneous formation of coumarin and pyrrole frameworks. The above syntheses are achieved via 1,3-dipolar cycloaddition reactions, Michael reaction, aza-Claisen rearrangement reactions, multi-component reactions (MCR), as well as metal-catalyzed reactions. Pyrrolocoumarins present cytotoxic, antifungal, antibacterial, α-glucosidase inhibition, antioxidant, lipoxygenase (LOX) inhibition, and fluorescent activities, as well as benzodiazepine receptor ability.

A facile synthesis of chromeno[3,4-c]spiropyrrolidine indenoquinoxalines via 1,3-dipolar cycloadditions

A one-pot, four-component reaction for the synthesis of novel chromeno[3,4-c]spiropyrrolidine-indenoquinoxalines is described via a 1,3-dipolar cycloaddition of 3-acetyl-coumarins with the azomethine ylides followed by deacetylation and protonation (deuteration). The products were obtained in moderate to high yields, and their structures were confirmed by 1H NMR, 13C NMR, FT-IR, and MS spectroscopy.

Azomethine Ylides-Versatile Synthons for Pyrrolidinyl-Heterocyclic Compounds

Azomethine ylides are nitrogen-based three-atom components commonly used in [3+2]-cycloaddition reactions with various unsaturated 2π-electron components. These reactions are highly regio- and stereoselective and have attracted the attention of organic chemists with respect to the construction of diverse heterocycles potentially bearing four new contiguous stereogenic centers. This review article complies the most important [3+2]-cycloaddition reactions of azomethine ylides with various olefinic, unsaturated 2π-electron components (acyclic, alicyclic, heterocyclic, and exocyclic ones) reported over the past two decades.

Perfluoroalkyl-Promoted Synthesis of Perfluoroalkylated Pyrrolidine-Fused Coumarins with Methyl β-Perfluoroalkylpropionates

Employing the methyl β-perfluoroalkylpropionate as the Michael acceptor, an efficient approach for the synthesis of perfluoroalkylated pyrrolidine-fused coumarins has been achieved. A tandem reaction involving [3 + 2] cycloaddition and intramolecular transesterification was proposed for the mechanism. The enhanced electrophilicity resulting from the strong electron-withdrawing ability of the perfluoroalkyl group was crucial for this tandem reaction.

Re-engineering natural products to engage new biological targets

Covering: up to 2020 Natural products have a long history in drug discovery, with their inherent biological activity often tailored by medicinal chemists to arrive at the final drug product. This process is illustrated by numerous examples, including the conversion of epothilone to ixabepilone, erythromycin to azithromycin, and lovastatin to simvastatin. However, natural products are also fruitful starting points for the creation of complex and diverse compounds, especially those that are markedly different from the parent natural product and accordingly do not retain the biological activity of the parent. The resulting products have physiochemical properties that differ considerably when compared to traditional screening collections, thus affording an opportunity to discover novel biological activity. The synthesis of new structural frameworks from natural products thus yields value-added compounds, as demonstrated in the last several years with multiple biological discoveries emerging from these collections. This Highlight details a handful of these studies, describing new compounds derived from natural products that have biological activity and cellular targets different from those evoked/engaged by the parent. Such re-engineering of natural products offers the potential for discovering compounds with interesting and unexpected biological activity.

Enantiomerically Enriched 1,2-P,N-Bidentate Ferrocenyl Ligands for 1,3-Dipolar Cycloaddition and Transfer Hydrogenation Reactions

Novel complexes of 1,2-P,N-bidentate ferrocenyl ligands with AgOAc or with [RuCl₂(PPh₃)₃] as catalysts have been studied in asymmetric synthesis. The catalytic activity of these systems have been studied in [3+2]-cycloaddition of azomethine ylides with olefins and the asymmetric transfer hydrogenation of ketones.

Diversity-oriented synthesis of chromenopyrrolidines from azomethine ylides and 2-hydroxybenzylidene indandiones via base-controlled regiodivergent (3+2) cycloaddition

An organobase-controlled, regiodivergent (3+2) cycloaddition resulting in two different cascade reactions is demonstrated from azomethine ylides and 2-hydroxybenzylidineindandiones to achieve diverse chromanopyrrolidines.

Enantioselective Synthesis of Polysubstituted Benzopyrano[3,4-c]pyrrolidine Frameworks via [3 + 2] Cycloaddition of Azomethine Ylides and Coumarin Derivatives

An enantioselective synthesis of benzopyrano[3,4-c]pyrrolidine derivatives via organocatalyzed [3 + 2] cycloaddition has been achieved. Cinchona alkaloid-derived organocatalysts as Brønsted bases have been examined for this asymmetric cycloaddition of o-hydroxy aromatic aldimines with 3-substituted coumarins. An unexpected rearrangement of the quaternary acyl moiety in the products resulted in an in situ protection of the o-hydroxy group.