Silver Trifluoromethanesulfonate-Catalyzed Annulation of Propargylic Alcohols with 3-Methyleneisoindolin-1-one

Rapid Synthesis of 3-Methyleneisoindolin-1-ones via Metal-Free Tandem Reactions of Ester-Functionalized Aziridines

We have disclosed a novel metal-free tandem cyclization reaction for the synthesis of 3-methyleneisoindolin-1-ones starting from ester-functionalized aziridines. This strategy can be effectively promoted by DBU and carboxylic acids. Mechanistically, it involves sequential ring opening of aziridines with carboxylic acids, lactamization, and elimination of carboxylic acids.

Syntheses of Minutuminolate and Related Coumarin Natural Products and Evaluation of Their TNF-α Inhibitory Activities

The concise syntheses of the coumarin natural product, minutuminolate (1), and its related natural products, 7-methoxy-8-(2-acetoxy-3-methyl-1-oxobut-2-enyl) coumarin (2) and muralatin I (3), were accomplished for the first time in 4-5 steps from the commercially available umbelliferone. The key step involves a palladium-catalyzed oxidative rearrangement reaction to assemble the α-acyloxyenone moiety in 1 and 2. The incorporation of this functionality enables the successful synthesis of coumarin 3 through an acidic hydrolysis reaction. The anti-inflammatory activities of the compounds were also evaluated against tumor necrosis factor-alpha production in lipopolysaccharides-stimulated RAW264.7 cells. Our developed synthetic route will facilitate the development of analogues and derivatives of 1-3 with potent anti-inflammatory activities.

Lewis-Acid-Mediated Intramolecular Cyclization of 4-Aryl-5-allyl-1,2,3-triazoles to Substituted Cyclopentene Derivatives

4-Aryl-5-allyl-N-fluoroalkyl-1,2,3-triazoles available by a three-component reaction of fluoroalkyl azides, copper acetylides, and allyl halides underwent aluminum halide-mediated transformation to N-(4-halo-2-aryl-cyclopentenyl) imidoyl halides by cyclization of vinyl cation intermediates, followed by halide capture. Utilization of the cyclic products was demonstrated by the synthesis of N-alkenyl amides, amidines, isoquinolines, and tetrazoles or by the subsequent modification of the cyclopentene ring.

Synthesis of Diversified Pyrazolo[3,4-b]pyridine Frameworks from 5-Aminopyrazoles and Alkynyl Aldehydes via Switchable C≡C Bond Activation Approaches

A cascade 6-endo-dig cyclization reaction was developed for the switchable synthesis of halogen and non-halogen-functionalized pyrazolo[3,4-b]pyridines from 5-aminopyrazoles and alkynyl aldehydes via C≡C bond activation with silver, iodine, or NBS. In addition to its wide substrate scope, the reaction showed good functional group tolerance as well as excellent regional selectivity. This new protocol manipulated three natural products, and the arylation, alkynylation, alkenylation, and selenization of iodine-functionalized products. These reactions demonstrated the potential applications of this new method.

Recent approaches for the synthesis of pyridines and (iso)quinolines using propargylic Alcohols

Propargylic alcohols are one of the readily available and highly explored building blocks in organic synthesis. They show distinct reactivities compared to simple alcohols and/or alkynes, and hence provide diverse possibilities to develop novel synthetic strategies for the construction of polycyclic systems, including heterocycles. The six-membered heterocycles, pyridines, quinolines, and isoquinolines, are very important privileged structures in medicinal chemistry and drug discovery due to their broad spectrum of biological activities. They are also part of vitamins, nucleic acids, pharmaceuticals, antibiotics, dyes, and agrochemicals. Many synthetic strategies have been developed for the rapid and efficient generation of these cyclic systems. One such strategy is employing the propargylic alcohols as reactants in the form of either a 3-carbon component or 2-carbon unit. Thus, in this review article, we aimed to summarize various approaches to pyridines, quinolines, and isoquinolines from propargylic alcohols. To the best of our knowledge, so far, no focused reviews have appeared on this topic in the literature. Due to the many reports available, we also restricted ourselves to the developments during the past 17 years, i.e., 2005-2021. We strongly believe that this review article provides comprehensive coverage of research articles on the title topic, and will be of great value for the organic synthetic community for further developments in this area of research.

Metal-Free Intramolecular [3+2] Cycloaddition of γ-Hydroxy Acetylenic Ketones with Alkynes for the Synthesis of Naphtho[1,2-c]furan-5-ones and Its Derivatization via a Selective C(sp2)-H Deuteration Reaction

A metal-free intramolecular [3+2] cycloaddtion has been achieved by treating benzene-linked propynol-ynes with AcOH/H₂O in a one-pot manner. The reaction provides greener, 100% atom-economic, highly regioselective, and more practical access to functionalized naphtho[1,2-c]furan-5-ones with valuable and versatile applications. The regioselective α-deuteration of naphtho[1,2-c]furan-5-ones has been also presented with excellent deuterium incorporation and chemical yields. Moreover, the fluorescent properties of naphtho[1,2-c]furan-5-one products have been investigated in solution.