Lewis Acid-Driven Multicomponent Reactions Enable 2-Alkyl Chromanones with Anticancer Activities

2-Alkyl chromanone scaffold has become prominent in pharmaceuticals and natural compounds. Consequently, devising robust strategies for synthesizing 2-alkyl chromanones remains crucial. Here, multicomponent reactions were employed to synthesize 2-alkyl chromanones containing an oxazole moiety using 3-formylchromones, amines, and N-propargylamides as reactants. This method utilizes readily available feedstocks with a catalytic amount of Zn(OTf)2 and exhibits an impressive substrate scope compared to existing methods. Importantly, the synthesized compounds demonstrated highly selective anticancer activity against the DU145 cell line.

Ru-catalyzed asymmetric hydrogenation of α,β-unsaturated ketones via a hydrogenation/isomerization cascade

Ru-catalyzed asymmetric hydrogenation of α-substituted α,β-unsaturated ketones has been developed for the enantioselective synthesis of chiral α-substituted secondary alcohols with high diastereo- and enantioselectivities (up to >99 : 1 dr, 98% ee). Mechanistic experiments suggest that the reaction proceeds via a Ru-catalyzed asymmetric hydrogenation of the CO bond in concert with a base-promoted allylic alcohol isomerization, and the final stereoselectivities were controlled by a DKR process during the asymmetric hydrogenation of the ketone intermediate.

Brasiliensic acid: in vitro cytotoxic and genotoxic, in vivo acute toxicity and in silico pharmacological prediction of a new promising molecule

Brasiliensic acid (Bras) is a chromanone isolated from Calophyllum brasiliense Cambèss. bark extracts with confirmed potential activity on gastric ulcer and Helicobacter pylori infection. This study aimed to investigate the in vitro and in vivo toxicity of Bras and molecular docking studies on its interactions with the H. pylori virulence factors and selected gastric cancer-related proteins. Cytotoxicity was evaluated by alamarBlue© assay, genotoxicity by micronucleus and comet assays, and on cell cycle by flow cytometry, using Chinese hamster epithelial ovary cells. Bras was not cytotoxic to CHO-K1 cells, and caused no chromosomal aberrations, nor altered DNA integrity. Furthermore, Bras inhibited damages to DNA by H2O2 at 1.16 µM. No cell cycle arrest was observed, but apoptosis accounted for 31.2% of the cell death observed in the CHO-K1 at 24 h incubation of the IC50. Oral acute toxicity by Hippocratic screening test in mice showed no relevant behavioral change/mortality seen up to 1,000 mg/kg. The molecular docking approach indicated potential interactions between Bras and the various targets for peptic ulcer and gastric cancer, notably CagA virulence factor of H. pylori and VEGFR-2. In conclusion, Bras is apparently safe and an optimization for Bras can be considered for gastric ulcer and cancer.Communicated by Ramaswamy H. Sarma.

Asymmetric Hydrogenations of Acyclic α,β-Unsaturated Ketones with Chiral Frustrated Lewis Pairs (FLPs)

In this paper, we demonstrate a metal-free asymmetric hydrogenation of acyclic α,β-unsaturated ketones under the catalysis of a frustrated Lewis pair (FLP) comprising chiral oxazoline and achiral borane. A wide range of optically active α-substituted ketones were furnished in high yields with 26-85% ee's.

Efficient Rh-Catalyzed Chemo- and Enantioselective Hydrogenation of 2-CF3-Chromen/Thiochromen-4-ones

A Rh-catalyzed highly chemo- and enantioselective hydrogenation of 2-CF3-chromen/thiochromen-4-ones was successfully established achieving excellent selectivity and high turnover numbers. Under mild conditions, a series of 2-CF3-chromen-4-ones were hydrogenated to provide the corresponding chiral 2-CF3-chroman-4-ones with excellent enantioselectivities (up to 99.9% ee) and achieve high turnover numbers (TON of up to 11,800). Moreover, the obtained hydrogenation products were also successfully transformed into other derivatives including the important intermediate of plasmepsin inhibitors with maintained enantiopurity.

Asymmetric synthesis of chiral (thio)chromanes and exploration on their structure-activity relationship in macrophages

A CuCl/(R,R)-Ph-BPE-catalyzed enantioselective hydroallylation of 2H-chromenes and 2H-thiochromenes with allylic phosphate electrophiles is developed, which enables highly efficient and atom-economical asymmetric access to a series of 4-allyl chromanes and thiochromanes in high yields (up to 91%) with excellent enantioselectivities (up to 99% ee). These valuable chiral chromane and thiochromane products can serve as crucial intermediates for accessing bioactive compounds containing oxygen and sulfur atoms. In addition, the antioxidant and anti-inflammatory effects of various chromanes and thiochromanes were investigated in RAW 264.7 macrophages. The chromanes and thiochromanes exhibited significant inhibitory effects on the production of reactive oxygen species (ROS) and the secretion of pro-inflammatory cytokines, including interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α). These findings indicate that the newly synthesized chromanes and thiochromanes hold promise as potential lead compounds for the development of antioxidant and anti-inflammatory drugs.

Catalytic Asymmetric Conjugate Reduction

Enantioselective reduction reactions are privileged transformations for the construction of trisubstituted stereogenic centers. While these include established synthetic strategies, such as asymmetric hydrogenation, methods based on the enantioselective addition of hydridic reagents to electrophilic prochiral substrates have also gained importance. In this context, the asymmetric conjugate reduction (ACR) of α,β-unsaturated compounds has become a convenient approach for the synthesis of chiral compounds with trisubstituted stereocenters in α-, β-, or γ-position to electron-withdrawing functional groups. Because such activating groups are diverse and amenable of further derivatizations, ACRs provide a general and powerful synthetic entry towards a variety of valuable chiral building blocks. This Review provides a comprehensive collection of catalytic ACR methods involving transition-metal, organic, and enzymatic catalysis since its first versions dating back to the late 1970s.

Synthetic and Computational Study of the Enantioselective [3+2]-Cycloaddition of Chromones with MBH Carbonates

Highly efficient and straightforward access to enantioenriched five-membered ring-fused chromanones is developed via [3+2]-cycloaddition of 3-cyanochromones with Morita-Baylis-Hillman carbonates. Densely functionalized chiral cyclopenta[b]chromanones with three continuous quaternary and tertiary stereogenic carbon centers were obtained in high yields with high ee and dr (≤97% yield, 97% ee, and >20:1 dr). Moreover, density functional theory calculations have been carried out to investigate the mechanism and regio- and diastereoselectivity of the reaction.

Asymmetric synthesis of flavanols via Cu-catalyzed kinetic resolution of chromenes and their anti-inflammatory activity

Flavanols are privileged heterocyclic compounds in medicinal chemistry. It is notable to develop an efficient and straightforward protocol for accessing chiral flavanols with precise control of the stereocenters. Here, a highly efficient kinetic resolution of chromenes was reported via Cu-catalyzed asymmetric hydroboration. This previously unidentified approach features a one-step synthesis of chiral flavan-3-ols containing two vicinal stereogenic centers via a highly efficient kinetic resolution (s factor up to 1060, >99% ee for most products). In addition, the anti-inflammation effects of these diversified flavan-3-ols were studied by the in vitro experiments and RNA sequencing analysis. These flavan-3-ols showed inhibitory effects on the secretion of pro-inflammation cytokines including interleukin-1β (IL-1β), IL-6, and tumor necrosis factor-α (TNF-α), as well as inhibiting the inflammation responses through down-regulating the gene transcriptions closely related to PI3K-Akt signaling pathway and TNF signaling pathway. The results suggested that these newly synthesized flavan-3-ols have the potential to be lead compounds for anti-inflammatory drugs.

Dynamic simulation of orientational disorder in organic crystals: methyl groups, trifluoromethyl groups and whole molecules

Large amplitude librations of atomic groups or of entire molecules in their crystals are simulated using optimized intermolecular potentials and crystal structures deposited in the Cambridge Structural Database. The analysis proceeds by a simple static model in which reorientations take place in a fixed environment, or by Monte Carlo (MC) simulation of equilibria dotted by rotational defects, or eventually by full Molecular Dynamics (MD). The simplest approach provides a valuable qualitative preview, but MC and MD are becoming easily accessible to the general solid-state chemist thanks to the facilities of the newly developed Milano Chemistry Molecular Simulation (MiCMoS) platform. Their combined results offer a wealth of information on the behaviour of phenyl-methyl and phenyl-trifluoromethyl groups, almost invariably affected by rotational flipping, whose nature and consequences are discussed with respect to disorder modelling in the refinement of X-ray structures. Whole-body reorientation takes place in flat molecules, benzene being the well-known prototype, but also in a very large molecule like coronene. Molecular dynamics of rotations in the cyclohexa-1,4-diene crystal offer a spectacular picture of the energetic profiles with jumping times. The dynamic oscillations described here are seldom considered in the formulation of crystal `bonds' or of `synthon' stability.

Unprecedented Rearrangement of β-difluoroboryloxy Ethers: A Route to C-2 alkyl-chromenones

The addition of boron-trifluoride etherate (BF3.OEt2) to allenic ketones has led to the isolation of the isolated boron-difluoride enolates. The single-crystal structure of boron-enolate has been solved. The unprecedented C1-C10-migration of (Z)-β-difluoroboryloxy ether derivatives is observed to deliver rearranged phenol derivatives which are functionalized to C-2 alkyl-chromenones. Interestingly the isolated boron-enolates have exhi-bited significant anticancer properties.

Facile access to chiral chromanone-2-carboxylic acids enabled by Rhodium-catalyzed chemo- and enantioselective hydrogenation

Rh-catalyzed highly chemo- and enantioselective hydrogenation of chromone-2-carboxylic acids was first successfully established, providing a wide range of enantiopure chromanone-2-carboxylic acids with excellent results (up to 97% yield and 99%...

Enantioselective Palladium-Catalyzed Hydrophosphinylation of Allenes with Phosphine Oxides: Access to Chiral Allylic Phosphine Oxides

A Pd-catalyzed hydrophosphinylation of alkyl and aryl-oxyallenes with phosphine oxides has been developed for the efficient and rapid construction of a family of chiral allylic phosphine oxides with a diverse range of functional groups. This methodology was further applied in the facile construction of chiral 2H-chromene and later stage functionalization of cholesterol.

Enantioselective synthesis of chiral 3-alkyl-3-nitro-4-chromanones via chiral thiourea-catalysed intramolecular Michael-type cyclization

Herein we report an enantioselective method for the rapid construction of chiral 3-nitro-4-chromanones via a chiral thiourea-catalyzed intramolecular Michael-type cyclization reaction. With this method, a series of 3,3-disubstituted-3-nitro-4-chromanones bearing contiguous C2/C3 stereocenters were obtained with high diastereoselectivities and good to excellent enantioselectivities. In vitro biological evaluations indicated that the chiral amide derivative of the product showed more potent antitumor activities than both the racemic and the corresponding enantiomers, showcasing the high influence of enantioselective methodology development toward medicinal studies.

Engaging yne-allenones in tunable catalytic silane-mediated conjugate transfer reductions

New tunable catalytic [2+2] cycloaddition/silane-mediated conjugate transfer reductions of yne-allenones have been developed, by which substituent-diverse cyclobutarenes with generally good yields were selectively synthesized by adjusting Fe-H and Cu-H catalytic systems. Use of the Fe-H system triggers 1,6-conjugate reduction to dihydrocyclobuta[a]naphthalen-4-ols whereas the Cu-H complex enables 1,4-conjugate reduction to cyclobuta[a]naphthalen-4(2H)-ones.

Enantio- and Regioselective CuH-Catalyzed Conjugate Reduction of Yne-Allenones

A new asymmetric catalytic conjugate reduction of yne-allenones to synthesize enantioenriched cyclobuta[a]naphthalen-4(2H)-ones has been established that uses copper-bisphosphine complexes as catalysts and gives excellent regio- and enantioselectivities (≥99% ee) in most cases. This protocol tolerates a broad scope of substrates, exhibits high compatibility with various substituents, and gives excellent stereoselectivity, providing a catalytic and efficient entry to fabrication of synthetically important chiral 6-6-4 tricarbocyclic scaffolds.

Metal-free access to 3-allyl-2-alkoxychromanones via phosphine-catalyzed alkoxy allylation of chromones with MBH carbonates and alcohols

A metal-free access to 3-allyl-2-alkoxychromanones by PPh₃-catalyzed alkoxy allylation of chromones with MBH carbonates and alcohols is described. This reaction is performed under mild conditions and it shows good functional group tolerance, providing a series of functionalized chromanones in moderate to high yields with excellent diastereoselectivities. Deuterium-labeling experiments to probe a possible mechanism and scale-up reaction were also conducted.

Synthesis of methanesulfone-containing tetrasubstituted carbon stereocenters

A methanesulfonylation reaction for the synthesis of sulfone-containing tetrasubstituted carbon stereocenters is described for the first time by simple treatment of indanedione-chromanone synthons with Et3N and easily accessible MsCl without any use of organometallic chemistry. This technology gave the corresponding valuable chromone-based 2-methanesulfonylated 1,3-indanediones in good yields (up to 89% yield) under mild conditions. The present work provides an attractive strategy for the construction of biologically interesting sulfone-containing tetrasubstituted carbon stereocenters, which might be valuable in medicinal chemistry.

Intramolecular Oxidative Coupling between Unactivated Aliphatic C-H and Aryl C-H Bonds

Direct oxidative coupling of different inert C-H bonds is the most straightforward and environmentally benign method to construct C-C bonds. In this paper, we developed a Pd-catalyzed intramolecular oxidative coupling between unactivated aliphatic and aryl C-H bonds. This chemistry showed great potential to build up fused cyclic scaffolds from linear substrates through oxidative couplings. Privileged chromane and tetralin scaffolds were constructed from readily available linear starting materials in the absence of any organohalides and organometallic partners.

Highly enantioselective access to chiral chromanes and thiochromanes via Cu-catalyzed hydroamination with anthranils

Highly efficient and atom-economic asymmetric access to 4-arylamino chromanes and thiochromanes bearing a benzylic alcohol functionality were developed by Cu(i)/(R,R)-Ph-BPE-catalyzed enantioselective hydroamination with anthranils.

Catalytic enantioselective synthesis of tetrasubstituted chromanones via palladium-catalyzed asymmetric conjugate arylation using chiral pyridine-dihydroisoquinoline ligands

Highly enantioselective conjugate addition reactions of arylboronic acids to 2-substituted chromones catalyzed by palladium complexes with new chiral Pyridine-Dihydroisoquinoline (PyDHIQ) ligands have been developed. These reactions provide highly enantioselective access to chromanones containing tetrasubstituted stereocenters. Various arylboronic acids and 2-substituted chromones can be used in the catalytic reaction to afford the chiral tetrasubstituted chromanones in good yields and excellent enantioselectivities (25 examples, up to 98% yields, up to 99% ee).

Conjugate Addition of Grignard Reagents to Thiochromones Catalyzed by Copper Salts: A Unified Approach to Both 2-Alkylthiochroman-4-One and Thioflavanone

Grignard reagents undergo conjugate addition to thiochromones catalyzed by copper salts to afford 2-substituted-thiochroman-4-ones, both 2-alkylthiochroman-4-ones and thioflavanones (2-arylthiochroman-4-ones), in good yields with trimethylsilyl chloride (TMSCl) as an additive. The best yields of 1,4-adducts can be attained with CuCN∙2LiCl as the copper source. Excellent yields of 2-alkyl-substituted thiochroman-4-ones and thioflavanones (2-aryl substituted) are attained with a broad range of Grignard reagents. This approach works well with both alkyl and aromatic Grignard reagents, thus providing a unified synthetic approach to privileged 2-substituted thiochroman-4-ones and a potential valuable precursor for further synthetic applications towards many pharmaceutically active molecules. The use of commercially available and/or readily prepared Grignard reagents will expedite the synthesis of a large library of both 2-alkyl substituted thiochroman-4-ones and thioflavanones for additional synthetic applications.

Asymmetric Hydrogenation of Ketones and Enones with Chiral Lewis Base Derived Frustrated Lewis Pairs

The concept of frustrated Lewis pairs (FLPs) has been widely applied in various research areas, and metal-free hydrogenation undoubtedly belongs to the most significant and successful ones. In the past decade, great efforts have been devoted to the synthesis of chiral boron Lewis acids. In a sharp contrast, chiral Lewis base derived FLPs have rarely been disclosed for the asymmetric hydrogenation. In this work, a novel type of chiral FLP was developed by simple combination of chiral oxazoline Lewis bases with achiral boron Lewis acids, thus providing a promising new direction for the development of chiral FLPs in the future. These chiral FLPs proved to be highly effective for the asymmetric hydrogenation of ketones, enones, and chromones, giving the corresponding products in high yields with up to 95 % ee. Mechanistic studies suggest that the hydrogen transfer to simple ketones likely proceeds in a concerted manner.

Cu(I)-Catalyzed Enantioselective Alkynylation of Thiochromones

A highly efficient asymmetric synthesis of chiral thiochromanones is developed via Cu(I)/phosphoramidite catalyzed asymmetric alkynylation of thiochromones under mild reaction conditions. The catalyst system is tolerant of various thiochromone precursors and terminal alkynes. The established asymmetric transformation provides different enatiomeric-enriched thiochromanones with more molecular complexity and enables access to chiral thioflavanones, a subgroup of flavonoid by further functionalization.

Gram-Scale Synthesis of 3-Sulfonyl Flavanones

In this paper, an easy-operational, high-yielding method for the gram-scale synthesis of 3-sulfonyl flavanones is described by a one-pot straightforward POCl₃ mediated intermolecular (5 + 1) annulation of the β-ketosulfones with an o-hydroxyaryl group (dual nucleophile) and arylaldehydes (dual electrophile) in refluxing toluene for 3 h. A plausible mechanism is proposed and discussed. This protocol provides a highly effective annulation via one carbon-oxygen (C-O) and one carbon-carbon (C-C) bond formations.

Thermal-mediated [1,3]-hydrogen transfer as the key step: access to oxindole-chromone hybrid collection with structural diversity

Inspired by the chemistry and biology of chromone and oxindole derivatives, herein we report the first example of thermal-mediated [1,3]-hydrogen transfer as the key step for the efficient synthesis of oxindole-chromone hybrid collections 2, which avoids additional catalyst and solvent conditions. All the oxindole-chromones 2 are smoothly obtained in >99% yields in all cases, avoiding column chromatography purification. In particular, the products 2 can act as potential synthons for further elaboration in structural diversity, which might be valuable in organic and medicinal chemistry.

Oxygen mediated highly efficient cobalt(ii) porphyrin-catalyzed reduction of functional chromones: experimental and computational studies

The highly efficient oxygen mediated reduction of functional chromones with sodium borohydride (NaBH₄) catalyzed by cobalt(ii) porphyrins afforded biologically active chroman-4-ols as the reduction products in 80–98% yields.