Facile synthesis of chiral 2-amino-4-(indol-3-yl)-4H-chromene derivatives using thiourea as the catalyst

N-Heterocyclic carbene-catalysed homoenolate addition reaction to 3-cyano-2-imino-2H-chromenes: synthesis of C4-functionalized 2-amino-3-cyano-4H-chromene

A NHC-catalyzed homoenolate addition reaction between enals and iminochromenes to yields of a new type of C4-functionalized 2-amino-4H-chromenes has been developed.

A rhodium-catalysed conjugate addition/cyclization cascade for the asymmetric synthesis of 2-amino-4H-chromenes

The enantioselective synthesis of 2-amino-4H-chromenes via the cascade rhodium-catalysed conjugate addition/hetero Thorpe-Ziegler reaction is reported. Moderate to good yields (up to 98%) and high enantioselectivities (up to 92% ee) were obtained with a chiral diene-coordinated rhodium complex as the catalyst. This protocol remedies the methodological deficiency in the asymmetric synthesis of 4-aryl 2-amino-4H-chromenes.

Synthesis and pharmacological properties of polysubstituted 2-amino-4H-pyran-3-carbonitrile derivatives

2-Amino-3-cyano-4H-chromenes are structural core motifs that received increasing attention in the last years due to their interesting potential pharmacological properties. In this review, the synthetic methods for these compounds are classified based on the type of catalyst in the pertinent reactions. In addition, the wide range of pharmacological properties of these compounds is covered in a separate section.

Enantioselective synthesis of novel pyrano[3,2-c]chromene derivatives as AChE inhibitors via an organocatalytic domino reaction

A series of optically active pyrano[3,2-c]chromenes have been synthesized through an asymmetric domino reaction of 4-hydroxy-2H-chromen-2-ones with malononitriles. The targeted molecules were obtained in excellent yields and enantioselectivities (up to 94% yield, 99% ee). The AChE inhibitory activity studies revealed that compounds 4n (IC₅₀ = 21.3 μM) and 4p (IC₅₀ = 19.2 μM) displayed potent acetylcholinesterase inhibition. In most cases, the S-enantiomers were superior to the corresponding R-enantiomers. Moreover, molecular modelling provides a practical method for understanding the enantioselective discrimination of AChE with these kinds of compounds.

Mn-mediated sequential three-component domino Knoevenagel/cyclization/Michael addition/oxidative cyclization reaction towards annulated imidazo[1,2-a]pyridines

The sequential three-component reaction between o-hydroxybenzaldehydes, N-(cyanomethyl)pyridinium salts and a nucleophile towards substituted chromenoimidazopyridines under oxidative conditions has been developed. The employment of Mn(OAc)₃·2H₂O or KMnO₄ as stoichiometric oxidants allowed the use of a wide range of nucleophiles, such as nitromethane, (aza)indoles, pyrroles, phenols, pyrazole, indazole and diethyl malonate. The formation of the target compounds presumably proceeds through a domino Knoevenagel/cyclization/Michael addition/oxidative cyclization reaction sequence.

Applications of N′-monofunctionalised TsDPEN derivatives in asymmetric catalysis

N′-Monoalkylated or N′-mono(thio)acylated(N-sulfonyl)-1,2-diphenylethylene-1,2-diamine (TsDPEN) derivatives are have found extensive applications in asymmetric catalysis of a wide range of synthetic applications.

Ammonia-Doped Polyaniline-Graphitic Carbon Nitride Nanocomposite as a Heterogeneous Green Catalyst for Synthesis of Indole-Substituted 4H-Chromenes

A nanocomposite of polyaniline with graphitic carbon nitride (GCN) nanosheets has been synthesized by a facile oxidative polymerization of an aniline monomer and GCN to demonstrate its potential to catalyze the synthesis of various indole-substituted 4H-chromenes. The synthesized nanocomposite was thoroughly characterized using different spectroscopic techniques to confirm the morphology and composition. Subsequently, the fabricated nanocomposite was used as a heterogeneous catalyst to synthesize several bioactive indole-substituted 4H-chromenes in an aqueous medium. Organic transformation under benign and environmentally sustainable conditions is of paramount importance in the view of growing environmental pollution. Water is the universal Green solvent and has been a preferred choice of nature to perform various reactions. The catalyst developed in this work showed very good recyclability and adaptability for the synthesis of various medicinally significant indole-substituted 4H-chromenes. This multicomponent reaction imparts very high atom economy (94%) and low environmental factor (0.13).

Regio- and diastereoselective synthesis of (E)-3-(2-aminochromen-4-yl)-6-aryl-substituted fulvenes

A practical base-catalyzed route was developed for the regio- and diastereoselective synthesis of (E)-3-aminochromene-6-aryl-disubstituted fulvenes in high yields up to 94% starting with the Michael addition of cyclopentadiene to 2-iminochromenes in the key step.

4-Dialkylaminopyridine modified magnetic nanoparticles: as an efficient nano-organocatalyst for one-pot synthesis of 2-amino-4H-chromene-3-carbonitrile derivatives in water

A new DMAP-based magnetic nano-organocatalyst was developed for efficient one-pot synthesis of 2-amino-4H-chromene-3-carbonitrile derivatives in water as a green solvent.

Novel ferrocene-based bifunctional amine-thioureas for asymmetric Michael addition of acetylacetone to nitroolefins

An efficient method was developed to synthesize ferrocene-based bifunctional amine-thioureas bearing multiple hydrogen-bonding donors. Asymmetric Michael addition of acetylacetone to nitroolefins catalyzed by these novel bifunctional catalysts affords the Michael adducts in high yield and moderate to excellent enantioselectivities. Multiple hydrogen-bonds play an important role in accelerating the reaction.

One-pot synthesis of tetrahydro-4H-chromenes by supramolecular catalysis in water

Tetrahydro-4H-chromenes were synthesizedviaan efficient one-pot three-component protocol by supramolecular catalysis with β-cyclodextrin in water.

Facile construction of 3-indolochromenes and 3-indoloxanthenes via EDDF catalyzed one-pot three component reactions

EDDF–ethylene glycol, an ambiphilic catalytic system has been employed for the mild and rapid synthesis of various 3-indolochromenes and 3-indoloxanthenesviaa one-pot MCR. Besides recyclability of the catalyst, the present method circumvents the formation of any by-products.

Strategies for the asymmetric functionalization of indoles: an update

During the past four years, the research of new synthetic methodologies for the rapid construction of enantiomerically pure substituted indole has had a fruitful and important growth.

l-Cysteine functionalized magnetic nanoparticles (LCMNP): a novel magnetically separable organocatalyst for one-pot synthesis of 2-amino-4H-chromene-3-carbonitriles in water

Magnetic nanoparticles were functionalized with l-cysteine using a new and efficient method and introduced as a novel magnetically separable organocatalyst.

K2CO3-mediated synthesis of functionalised 4-substituted-2-amino-3-cyano-4H-chromenes via Michael-cyclization reactions

An efficient approach for the synthesis of functionalized 4-substituted-2-amino-3-cyano-4H-chromenes moderate to high yields (up to 98%) has been achieved via a tandem K2CO3 catalyzed conjugate addition-cyclization reaction of malononitrile and a range of Knoevenagel adducts previously formed from oxindole, pyrazolone, nitromethane, N,N-dimethylbarbituric acid or indanedione. This methodology differs from the previous classical methods in its simplicity and ready availability of the catalyst.

Ferrocene as a scaffold for effective bifunctional amine–thiourea organocatalysts

This work demonstrates that ferrocene could be an excellent scaffold for chiral organocatalysts.

Synthesis of functional 4H-chromenes from phenols and acetophenones under solvent- and metal-free conditions

Sulfuric-acid-promoted tandem reaction of phenols with acetophenones under solvent- and metal-free conditions has been developed, which afforded functional 4H-chromenes in good yields with water as the side product.