Facile synthesis of densely substituted chroman derivatives through Brønsted acid ionic liquid catalyzed three-component reactions of aromatic aldehydes, 1,1-diarylethylenes and nucleophiles

Cooperative Catalysis-Enabled (4 + 3) Cycloaddition of 2-Indolylmethanols with In Situ-Generated ortho-Naphthoquinone Methides

A cooperative catalysis-enabled (4 + 3) cycloaddition of 2-indolylmethanols with ortho-naphthoquinone methides (o-NQMs), which were in situ-generated from enynones, has been established in the presence of silver/Brønsted acid cocatalysts. In the reaction pathway, the key o-NQM intermediates were formed through Ag(I)-catalyzed cyclization of enynones, while the indole-based carbocation intermediates were generated via Brønsted acid-catalyzed dehydration of 2-indolylmethanols. By this approach, a wide range of seven-membered cyclohepta[b]indoles were synthesized in good yields with high efficiency under mild reaction conditions, which serves as a useful strategy toward constructing indole-fused seven-membered rings. Moreover, the catalytic asymmetric version of this (4 + 3) cycloaddition has been realized under the cooperative catalysis of Ag(I) with chiral phosphoric acid, which offered chiral cyclohepta[b]indole with a good enantioselectivity (75% ee). This work not only represents the first cooperative catalysis-enabled (4 + 3) cycloaddition of 2-indolylmethanols but also provides a good example for o-NQM-involved cycloadditions, which will contribute to the chemistry of 2-indolylmethanols and enrich the research contents of cooperative catalysis.

Streamlining efficient and selective synthesis of benzoxanthenones and xanthenes with dual catalysts on a single support

Using two catalysts on a single support can improve reaction efficiency, higher yields, improved selectivity, and simplified reaction conditions, making it a valuable approach for industrial transformation. Herein, we describe the development of a novel and effective heterogeneous catalyst, WCl6/CuCl2, supported on graphitic carbon nitride (W/Cu@g-C3N4), which was synthesized under hydrothermal conditions. The structure and morphology properties of the W/Cu@g-C3N4 were characterized using various spectroscopic techniques, including FTIR, XRD, TEM, TGA, EDX, and SEM. The W/Cu@g-C3N4 support material enabled the rapid and efficient synthesis of benzoxanthenones and xanthenes derivatives in high yields under mild reaction conditions and short reaction times. The W/Cu@g-C3N4 catalyst was also found to be easily recyclable, and its catalytic performance did not significantly decrease after five times use. The findings suggest that W/Cu@g-C3N4 is a promising chemical synthesis catalyst with significant implications for sustainable and cost-effective organic synthesis.

Binding and thermodynamic study of thalidomide with calf thymus DNA: Spectroscopic and computational approaches

The thalidomide-DNA interactions have been investigated in detail by numerous biophysical techniques such as UV-vis, dye displacement assay, viscosity, cyclic voltammetry, circular dichroism, molecular docking, molecular dynamic simulation, FT-IR and ¹H NMR spectroscopy. CD spectroscopy, thermal denaturation and viscosity measurement explained that thalidomide is groove binder. Molecular docking analysis highlighted that thalidomide binds trough minor groove of calf thymus DNA which also confirmed from dye displacement experiment. To our knowledge, this is the first instance thalidomide was shown to binds with calf thymus DNA. Molecular dynamic simulation indicated that the thalidomide-DNA system was stabilized by electrostatic attraction as the main interaction and mode of binding is minor groove. Our study provides a better understanding to the DNA-thalidomide binding affinity and it mechanism. Overall, all these in formations can be used for further understanding the pharmacological effects of thalidomide.

Access to Electron-Deficient 2,2-Disubstituted Chromanes: A Highly Regioselective One-Pot Synthesis via an Inverse-Electron-Demand [4 + 2] Cycloaddition of ortho-Quinone Methides

We report the one-pot synthesis of 2,2-disubstituted chromanes with electron-withdrawing substituents. This reaction provides a simple yet efficient route to a wide range of electron-deficient chromanes in high yield and excellent regioselectivity. The reaction of salicylaldehyde with 1,1-disubstituted ethylenes smoothly furnishes these electron-deficient chromanes, which can be further transformed into functionalized chromanes or chromene. For example, BW683C was effectively synthesized from 5-chlorosalicylaldehyde with 4-chlorostyrene in two steps in excellent yield. The present reaction thus provides versatile access to functionalized electron-deficient chromanes and chromenes and therefore constitutes a promising tool for the synthesis of biologically and photochemically active molecules.

A Strategy To Obtain o-Naphthoquinone Methides: Ag(I)-Catalyzed Cyclization of Enynones for the Synthesis of Benzo[ h]chromanes and Naphthopyryliums

A new strategy to obtain o-NQM intermediates through a ring-formation strategy by Ag(I)-catalyzed cyclization of 2-alkenylphenyl alkynyl ketones and its [4 + 2] annulations with styrenes has been developed. This reaction features high efficiency, mild reaction conditions, as well as flexible substitutions and atom economy. The obtained benzo[ h]chromane products were further oxidized to naphthopyryliums, which displayed tunable photophysical properties.

Recent advances in the application of indoles in multicomponent reactions

Indoles are some of the most versatile and common nitrogen-based heterocyclic scaffolds and are frequently used in the synthesis of various organic compounds. Indole based compounds are very important among heterocyclic structures due to their biological and pharmaceutical activities. The last decade, in particular, has witnessed considerable activity towards the synthesis of indole derivatives due to the possibilities for the design of polycyclic structures by the incorporation of multiple fused heterocyclic scaffolds in an attempt to achieve promising new heterocycles with chemical and biomedical relevance. In this study, we provide an overview on recent applications of indole in the multicomponent reactions for the synthesis of various heterocyclic compounds during the period of 2012 to 2017.

Diastereoselective construction of 4-indole substituted chromans bearing a ketal motif through a three-component Friedel–Crafts alkylation/ketalization sequence

The first TfOH-catalyzed three-component Friedel–Crafts alkylation/ketalization sequence of indoles, alcohols and ortho-hydroxychalcones was developed to afford a wide range of 4-indole substituted chromans bearing a ketal motif in 77–99% yields. Notably, only a simple filtration was needed to purify them. By altering methanol to CHCl₃, 2,4-bisindole substituted chroman with the same indole substituent at the C2 and C4 positions was afforded. Moreover, 2,4-bisindole substituted chromans with different indole substituents could be obtained by treatment of 4-indole monosubstituted chromans with another indole molecule.

The first TfOH-catalyzed three-component Friedel–Crafts alkylation/ketalization sequence of indoles, alcohols and ortho-hydroxychalcones was developed to afford a wide range of 4-indole substituted chromans bearing a ketal motif in 77–99% yields.

Donor–acceptor cyclopropanes as ortho-quinone methide equivalents in formal (4 + 2)-cycloaddition to alkenes

A new reactivity of donor–acceptor cyclopropanes as synthetic equivalents of o-quinone methides was revealed for 2-hydroxyarylcyclopropane diesters in their formal (4 + 2)-cycloaddition to alkenes yielding chromanes.