Electrorearranged Difunctionalization of 4-Hydroxy-α-benzopyrones.

We herein report the exploration of an electrosynthetic strategy as a highly efficient and straightforward alternative protocol for accessing diversely substituted and biologically promising alkyl 2-hydroxy-3-oxo-2,3-dihydrobenzofuran-2-carboxylates through an electrorearranged difunctionalization of 4-hydroxycoumarins, involving the singlet oxygen insertion from molecular oxygen, at ambient temperature. The present method is notably more advantageous than the previously reported photochemical conversion regarding yields and reaction times, substrate scope and functional group tolerability, operational simplicity, and scalability.

Mechanochemical Solvent-Free One-Pot Synthesis of Poly-Functionalized 5-(Arylselanyl)-1H-1,2,3-triazoles Through a Copper(I)-Catalyzed Click Reaction.

A mechanochemistry-driven practical and efficient synthetic protocol for accessing diverse series of biologically relevant poly-functionalized 5-(arylselanyl)-1H-1,2,3-triazoles through copper(I)-catalyzed click reaction between aryl/heteroaryl acetylenes, diaryl diselenides, benzyl bromides, and sodium azide has been accomplished under high-speed ball-milling. Advantages of this method include operational simplicity, avoidance of using solvent and external heating, one-pot synthesis, short reaction time in minutes, good to excellent yields, broad substrate scope, and gram-scale applications. Furthermore, synthesized organoselenium compounds were synthetically diversified to biologically promising selenones.

Electrochemical Regioselective C(sp2)-H Selenylation and Sulfenylation of Substituted 2-Amino-1,4-naphthoquinones.

A straightforward and efficient electrochemical method for regioselective C(sp2)-H selenylation and sulfenylation of substituted 2-amino-1,4-naphthoquinones has been unearthed. This oxidative cross-coupling reaction avoids using transition metal catalysts, oxidants, and high temperatures. The other notable advantages of this protocol are the tolerance of diverse functional groups, mild reaction conditions at ambient temperature, energy efficiency, good to excellent yields, short reaction times (in minutes), gram-scale applicability, and eco-friendliness.

Visible-Light-Promoted Intramolecular C-O Bond Formation via Csp3-H Functionalization: A Straightforward Synthetic Route to Biorelevant Dihydrofuro[3,2-c]chromenone Derivatives.

A photochemical method for the synthesis of functionalized dihydrofuro[3,2-c]chromenones via intramolecular Csp3-H cross-dehydrogenative oxygenation within a warfarin framework has been unearthed. Advantages of this protocol include abundant sunlight or low-energy visible light as the energy source, mild reaction conditions, and avoidance of metal catalysts.

An Updated Review on Biologically Promising Natural Oxepines.

Benzo-oxepines and dibenzo-oxepines, a unique class of naturally occurring secondary metabolites, are distributed mainly in plants and fungi and have received much attention from phytochemists and biologists based on their fascinating structural features and health-promoting functions. This review summarizes 100 oxepine derivatives comprising three categories: benzo-oxepine, dibenzo-oxepine, and pyrano-oxepine. Studies on various structural features and pharmacological activities of oxepine derivatives promote further in-depth research on these potent natural products. This review portrays the natural occurrence, bioactivity and biosynthesis of oxepines reported from 1984 to 2021.

Visible Light-Driven and Singlet Oxygen-Mediated Photochemical Cross-Dehydrogenative C3-H Sulfenylation of 4-Hydroxycoumarins with Thiols Using Rose Bengal as a Photosensitizer.

A visible light (white light-emitting diode/direct sunlight)-driven photochemical synthesis of a new series of biologically interesting 3-(alkyl/benzylthio)-4-hydroxy-2H-chromen-2-ones has been achieved through a cross-dehydrogenative C3-H sulfenylation of 4-hydroxycoumarins with thiols at ambient temperature in the presence of rose bengal in acetonitrile under an oxygen atmosphere. The notable features of this newly developed method are mild reaction conditions, energy efficiency, metal-free synthesis, good to excellent yields, use of low-cost materials, and eco-friendliness.

Visible Light-Induced and Singlet Oxygen-Mediated Photochemical Conversion of 4-Hydroxy-α-benzopyrones to 2-Hydroxy-3-oxo-2,3-dihydrobenzofuran-2-carboxamides/carboxylates Using Rose Bengal as a Photosensitizer.

Development of a visible light-induced and singlet oxygen-mediated green protocol has been accomplished for the first time for the photochemical transformation of 4-hydroxy-α-benzopyrones to a new series of biorelevant 2-hydroxy-3-oxo-2,3-dihydrobenzofuran-2-carboxamides and 2-hydroxy-3-oxo-2,3-dihydrobenzofuran-2-carboxylates using rose bengal as a triplet photosensitizer at ambient temperature. Metal-free one-pot synthesis, broader substrate scope, good-to-excellent yields, use of cost-effective and eco-friendly starting materials and photosensitizer, and energy efficiency are the salient features of this newly developed method.

Series of Functionalized 5-(2-Arylimidazo[1,2-a]pyridin-3-yl)pyrimidine-2,4(1H,3H)-diones: A Water-Mediated Three-Component Catalyst-Free Protocol Revisited.

A water-mediated and catalyst-free practical method for the synthesis of a new series of pharmaceutically interesting functionalized 5-(2-arylimidazo[1,2-a]pyridin-3-yl)pyrimidine-2,4(1H,3H)-diones has been accomplished based on a one-pot multicomponent reaction between arylglyoxal monohydrates, 2-aminopyridines/2-aminopyrimidine, and barbituric/N,N-dimethylbarbituric acids under reflux conditions. The salient features of this protocol are avoidance of any additive/catalyst and toxic organic solvents, use of water as reaction medium, clean reaction profiles, operational simplicity, ease of product isolation/purification without the aid of tedious column chromatography, good to excellent yields, and high atom-economy and low E-factor.

Design of Organic Transformations at Ambient Conditions: Our Sincere Efforts to the Cause of Green Chemistry Practice.

This account summarizes our recent efforts in designing a good number of important organic transformations leading to the synthesis of biologically relevant compounds at room temperature and pressure. Currently, the concept of green chemistry is globally acclaimed and has already advanced quite significantly to emerge as a distinct branch of chemical sciences. Among the principles of green chemistry, one principle is dedicated to the "design of energy efficiency" - that is, to develop synthetic strategies that require less or the minimum amount of energy to carry out a specific reaction with optimum productivity - and the most effective way to save energy is to develop strategies/protocols that are capable enough to carry out the transformations at ambient temperature! As part of on-going developments in green synthetic strategies, the design of reactions under ambient conditions coupled with other green aspects is, thus, an area of current interest. The concept of developing reaction strategies at room temperature and pressure is now an emerging field of research in organic chemistry and is progressing steadily. This account is aimed to offer an overview of our recent research works directly related to this particular field of interest, and highlights the green chemistry practice leading to carbon-carbon and carbon-heteroatom bond-forming reactions of topical significance. Green synthetic routes to a variety of biologically relevant organic molecules (heterocyclic, heteroaromatic, alicyclic, acyclic, etc.) at room temperature and pressure are discussed.

In vitro evaluation and in silico screening of synthetic acetylcholinesterase inhibitors bearing functionalized piperidine pharmacophores.

A series of densely functionalized piperidine (FP) scaffolds was synthesized following a diastereoselective one-pot multicomponent protocol under eco-friendly conditions. The FPs were evaluated in vitro for their acetylcholinesterase (AChE) inhibitory activity, and in silico studies for all the target compounds were carried out using pharmacophore mapping, molecular docking and quantitative structure-activity relationship (QSAR) analysis in order to understand the structural features required for interaction with the AChE enzyme and the key active site residues involved in the intermolecular interactions. Halogenation, nitration or 3,4-methylenedixoxy-substitution at the phenyl ring attached to the 2- and 6-positions of 1,2,5,6-tetrahydropyridine nucleus in compounds 14-17, 19, 20, 24 and 26 greatly enhanced the AChE inhibitory activity. The docking analysis demonstrated that the inhibitors are well-fitted in the active sites. The in silico studies enlighten the future course of studies in modifying the scaffolds for better therapeutic efficacy against the deadly Alzheimer's disease.

Crystal structure of 5,5'-[(4-fluoro-phen-yl)methyl-ene]bis-[6-amino-1,3-di-methyl-pyrimidine-2,4(1H,3H)-dione].

In the title mol-ecule, C19H21FN6O4, the dihedral angles between the benzene ring and essentially planar pyrimidine rings [maximum deviations of 0.036 (2) and 0.056 (2) Å] are 73.32 (7) and 63.81 (8)°. The dihedral angle between the mean planes of the pyrimidine rings is 61.43 (6)°. In the crystal, N-H⋯O hydrogen bonds link mol-ecules, forming a two-dimensional network parallel to (001) and in combination with weak C-H⋯O hydrogen bonds, a three-dimensional network is formed. Weak C-H⋯π inter-actions and π-π inter-actions, with a centroid-centroid distance of 3.599 (2) Šare also observed.

Ethyl 6-amino-5-cyano-4-phenyl-2,4-di-hydro-pyrano[2,3-c]pyrazole-3-carboxyl-ate dimethyl sulfoxide monosolvate.

In the asymmetric unit of the title compound, C16H14N4O3·C2H6OS, there are two independent main mol-ecules (A and B) and two dimethyl sulfoxide solvent mol-ecules. In mol-ecule A, the pyran ring is in a flattened sofa conformation, with the sp (3)-hydridized C atom forming the flap. In mol-ecule B, the pyran ring is in a flattened boat conformation, with the sp (3)-hydridized C atom and the O atom deviating by 0.073 (3) and 0.055 (3) Å, respectively, from the plane of the other four atoms. The mean planes the pyrazole and phenyl rings form dihedral angles of 84.4 (2) and 84.9 (2)°, respectively, for mol-ecules A and B. In the crystal, N-H⋯O and N-H⋯N hydrogen bonds link the components of the structure into chains along [010]. In both solvent mol-ecules, the S atoms are disordered over two sites, with occupancy ratios of 0.679 (4):0.321 (4) and 0.546 (6):0.454 (6).

6-Amino-3-methyl-4-(3,4,5-tri-meth-oxy-phen-yl)-2,4-di-hydro-pyrano[2,3-c]pyrazole-5-carbo-nitrile.

In the title compound, C17H18N4O4, the dihedral angle between the benzene ring and 2,4-di-hydro-pyrano[2,3-c]pyrazole ring system is 89.41 (7)°. The pyran moiety adopts a strongly flattened boat conformation. In the crystal, mol-ecules are linked by N-H⋯N, N-H⋯O, C-H⋯N and C-H⋯O hydrogen bonds into an infinite two-dimensional network parallel to (110). There are π-π inter-actions between the pyrazole rings in neighbouring layers [centroid-centroid distance = 3.621 (1) Å].

2-[4-(Piperidin-1-yl)-5H-chromeno[2,3-d]pyrimidin-2-yl]phenol.

In the title compound, C22H21N3O2, the pyrimidine ring is essentially planar [maximum deviation = 0.018 (2) Å] and forms dihedral angles of 22.70 (8) and 0.97 (7)°, respectively, with the fused benzene ring and the hy-droxy-substituted benzene ring. The piperidine ring has a chair conformation and the pyran ring has a flattened twist-boat conformation. The hy-droxy group was refined as disordered over two sets of sites in a 0.702 (4):0.298 (4) ratio. The disorder corresponds to a rotation of approxomiately 180° about the C-C bond connecting the phenol group to the pyrimidine ring and hence, both the major and minor components of disorder form intra-molecular O-H⋯N hydrogen bonds. In the crystal, pairs of weak C-H⋯π inter-actions form inversion dimers. In addition, π-π inter-actions are observed between the pyrimidine ring and the hy-droxy-substituted benzene ring [centroid-centroid separation = 3.739 (2) Å].

Practice of green chemistry strategies in synthetic organic chemistry: a glimpse of our sincere efforts in green chemistry research.

This feature article summarises our recent contributions (2019-2023) in designing and developing a handful of promising organic transformations for accessing several diversely functionalised biologically relevant organic scaffolds, following the green chemistry principles, particularly focusing on the application of low-energy visible light, electrochemistry, ball-milling, ultrasound, and catalyst- and additive-free synthetic strategies.

Ethyl 4-anilino-2,6-bis-(4-fluoro-phen-yl)-1-phenyl-1,2,5,6-tetra-hydro-pyridine-3-carboxyl-ate.

In the title compound, C(32)H(28)F(2)N(2)O(2), the tetra-hydro-pyridine ring adopts a distorted boat conformation. The two fluoro-phenyl groups are attached to the tetra-hydro-pyridine ring in a trans orientation. The dihedral angle between the planes of the fluoro-substituted rings is 57.0 (1)°. The amino group and carbonyl O atom are involved in intra-molecular hydrogen bonding. In the crystal, weak C-H⋯O, C-H⋯F and C-H⋯π inter-actions link the mol-ecules into columns along [010].

Methyl 4-(4-fluoro-anilino)-1,2,6-tris-(4-fluoro-phen-yl)-1,2,5,6-tetra-hydro-pyri-dine-3-carboxyl-ate.

In the title mol-ecule, C31H24F4N2O2, the tetra-hydro-pyridine ring adopts a distorted boat conformation. An intra-molecular N-H⋯O hydrogen bond is formed by the amino group and ccarboxyl C=O atom. The crystal structure features weak C-H⋯F and C-H⋯O inter-actions.

Ethyl 2,6-bis-(4-chloro-phen-yl)-4-(4-methyl-anilino)-1-(4-methyl-phen-yl)-1,2,5,6-tetra-hydro-pyridine-3-carboxyl-ate.

In the title mol-ecule, C34H32Cl2N2O2, the tetra-hydro-pyridine ring adopts a distorted boat conformation and both 4-chloro-phenyl substituents are in axial positions. An intra-molecular N-H⋯O hydrogen bond is formed by the amino group and carbonyl O atom. In the crystal, weak C-H⋯Cl inter-actions link the mol-ecules into chains along [010].

Ethyl 2,6-bis-(4-chloro-phen-yl)-4-(4-fluoro-anilino)-1-(4-fluoro-phen-yl)-1,2,5,6-tetra-hydro-pyridine-3-carboxyl-ate.

In the title compound, C32H26Cl2F2N2O2, the tetra-hydro-pyridine ring adopts a distorted boat conformation. The chlorophenyl rings are inclined to one another by 55.2 (1)°, while for the fluorophenyl rings the dihedral angle is 80.7 (1)°. The amino group and carbonyl O atom are involved in an intra-molecular N-H⋯O hydrogen bond. In the crystal, weak C-H⋯O, C-H⋯F and C-H⋯Cl inter-actions link the mol-ecules into a three-dimensional network.

C(sp)-C(sp3) Bond Formation through Ligand- and Additive-Free CuO-Mediated Decarboxylative Direct Cross-Coupling of Coumarin-/Chromone-3-carboxylic Acids and Terminal Alkynes.

A practical and efficient method for the synthesis of functionalized 4-(aryl-/heteroaryl-ethynyl)chroman-2-ones and 2-(aryl-/heteroaryl-ethynyl)chroman-4-ones through copper-catalyzed decarboxylative direct cross-coupling of coumarin-/chromone-3-carboxylic acids with terminal alkynes, leading to the formation of C(sp)-C(sp3) bonds, has been unearthed. Advantages of this protocol include avoidance of any ligands and bases, a broad substrate scope, tolerance of diverse functional groups, and good to excellent yields.