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A convenient one-pot, two-step methodology was developed for the transformation of readily available planar naphthoquinone derivatives into structurally complex indole-fused nitrogen heterocycles under aerobic conditions.

Regioselective vicinal difunctionalization of diverse alkene derivatives was successfully carried out using readily available carboxylic acids.

Designer micellar medium was explored for the transformation of diverse anilines to the corresponding densely substituted biologically relevant skatole derivatives in an aqueous medium via 5-exo-trig cyclization reaction. The scope of the reaction was extended to intermolecular Csp2-Csp2 and Csp2-N bond forming reactions in water. Systematic investigations revealed that altering hydrophobicity of surfactant influences the yield of both C C and C N bond forming reactions in water.

Unprecedented acceleration in the rate of the N-heterocyclic carbene (NHC) organocatalysis was observed while performing the reaction in water medium with NaCl as an additive during the synthesis of diverse spirooxindole-γ-butyrolactone derivatives. The seminal role of hydrophobic hydration effect for the acceleration of the reaction was further proved by performing the reaction with antihydrophobic additive LiClO4 and using denser D2O solvent.

Stearyl MethoxyPEGglycol Succinate (SMPS), a designer micellar medium, was reported for organic transformations in an environmentally benign water medium. Phytotoxicity, bacteria toxicity, and aquatic toxicity assays revealed that SMPS was nontoxic. Excellence in organic transformation was reported through the reduction of lipophilic nitroarenes and through the syntheses of aniline tethered indole derivatives with good to excellent yields.

Single crystal X-ray analysis reveals that the 9-(2-hydroxy-4,4-dimethyl-6-oxocyclohex-1-en-1-yl)-3,3-dimethyl-2,3,4,9-tetrahydro-1H-xanthen-1-one, crystallizes in the centrosymmetric space group P21/c. In the crystal, molecules form as a dimer through a keto-enol type hydrogen-bonding pattern along with intermolecular C H⋯O interactions. The crystal structure of the title compound is further stabilized by intermolecular H⋯H interactions. Various intermolecular interactions present in the crystal structure are quantified by Hirshfeld surface analysis, PIXEL energy, NBO, AIM and DFT calculations. The energetics of the title compound is also compared with that of the two closely related analogs. Further, the vibrational modes of the interacting groups are characterized using both the experimental and simulated FT-IR and FT-Raman spectra. The experimental and calculated UV–visible spectra are compared and agree well. The time-dependent DFT spectra suggest that the ligand-to-ligand charge transfer within the molecule is responsible for the intense absorbance.

6-Exo-trig cyclization reaction through regioselective carbopalladation was demonstrated with N-(2-halobenzyl)-N-allylamines to furnish the corresponding C4-substituted tetrahydroisoquinoline derivatives. The scope of the reaction was extended to the synthesis of C4-quaternary tetrahydroisoquinoline derivatives also. The nature of the substituent on the olefin moiety dictates the course of the carbopalladation sequence. Regioselective carbopalladation is substantiated by performing the reaction with unsymmetrical diallylated amine substrates.

Palladium catalysed addition of arylboronic acid to the readily available 2-cyano-(N-aryl)-acetamide or ethyl-2-cyanoacetate followed by subsequent reaction transform them into the biologically significant 4-arylquinolin-2-one or pyrazolone derivatives. The reaction conditions are robust enough to prevent the hydrolysis of ester/amide moiety during arylation. In addition, the unactivated nitrile moiety in the acetonitrile also converted to the corresponding acetophenone derivative.

Two different classes of compounds namely xanthenedione and acridinedione derivatives have been synthesized and crystal structures of these compounds (9-(p-tolyl)-3,4,5,6,7,9-hexahydro-1H-xanthene-1,8(2H)-dione, C20H20O3, 1 and 9-(p-tolyl)-3,4,6,7,9,10-hexahydroacridine-1,8(2H,5H)-dione, C20H21NO2, 2) are reported. The X-ray analysis reveals that the central heterocyclic ring exhibits boat conformation and the cyclohexene rings have envelope conformations in both structures. The Hirshfeld surface analysis suggests that the relative contribution of H···H, H···O and H···C contacts have not changed due to the positional isomers (ortho and para) of 1. The same is true when NH group replaces the O atom in the central ring as well. The PIXEL energy analysis suggests that the intermolecular C–H···O and C–H···C(π) interactions stabilize the crystal structure of 1. In 2, the intermolecular N–H···O, C–H···O and C–H···C(π) interactions existing in different dimers. The isostructurality analysis indicates that the structure 1 shares 2D isostructurality with one of its closely related structure, whereas structure 2 shares only 0D isostructurality with its closely related structure. The lattice energy calculation for 1 and its ortho isomer and compound 2 is reported. The energy frameworks analysis was performed in order to visualize the topology of the energy frameworks for these crystals. The topological analysis is presented for intermolecular interactions existing in 1 and 2. The frontier molecular orbital analysis suggests that the HOMO orbital's localization shows distinct features for 1 and 2.

The excellent surface catalytic potential of Fe3O4–OSO3H is utilized in the synthesis of symmetrically and unsymmetrically substituted urea derivatives via transamidation reactions. The scope of the surface catalysis is further extended in transamidation reactions of cyclic and acyclic amide derivatives, and in the amidation of fatty acids. In both transamidation and amidation reactions, the catalyst is reusable up to five times without significant loss in its activity.

A peroxide-free methodology was developed for the synthesis of benzoylated naphthol/phenol derivatives through oxidative deamination reaction performed under aerobic reaction conditions. A synergistic combination of Cu(OTf)2 and Ag2O was used to convert the aminonaphthols and aminophenols to the corresponding benzoylated derivatives. The definite role of atmospheric oxygen to assist the reaction was proved by performing the reaction in the argon atmosphere.

Additional file 1. Additional tables and figures.

Increased expression of efflux transport proteins confers the Multi Drug Resistant (MDR) phenotype to drug resistant bacteria, which can be mitigated by efflux pump inhibitors (EPI). EPI's have the dual advantage of restoring efficacy of antibiotics and retarding the evolution of drug resistant mutants. In this study, 17 heterocyclic derivatives synthesized by a polyethylenimine (PEI) catalyzed one-pot protocol were evaluated for their EPI potential. Based on in silico studies and in vitro studies, 5 benzochromene (BC) based compounds (among 17 heterocyclic derivatives), were observed to significantly potentiate the effect of ciprofloxacin (CPX) and displayed a best modulation factor of 32, against the NorA overexpressed mutant SA-1199B. Toxicity analyses using the zebrafish model showed that, from all the benzochromene compounds evaluated, BC9 exhibited low toxicity. BC9 inhibited the NorA efflux pump at a minimum effective concentration (MEC) of 2 μg ml−1 (4.03 μM) and even at subinhibitory concentrations, and it was effective in reversing the CPX MIC of both the ATCC strain and a clinical isolate of MRSA by 128 and 4 fold respectively. Our results show that benzochromene derivative BC9 is a highly specific NorA inhibitor that can be employed to mitigate MDR strains of S. aureus that overexpress the NorA efflux pump.

Fe 3 O 4 -OSO 3 H was identified as an efficient reusable catalyst for the facile synthesis of diarylmethyl indole derivatives under neat condition by C–C bond forming reaction. Fe 3 O 4 -OSO 3 H catalysis was further extended to C–N bond forming reactions and for the synthesis of spermicidal 3,3′-di(indolyl)oxindole derivative. All the products were obtained in good to excellent yields.

Copper(II) chloride is utilized to carry out ligand-free one-pot synthesis of triarylmethane derivatives in moderate to good yields. Copper(II) chloride also facilitated the transformation of both bis(indolyl)methane and leuco base to the corresponding triarylmethane derivatives by aryl group transfer. Based on the observed aryl transfer, an easy access to triarylmethane derivatives is devised by treating an equimolar mixture of bis(indolyl)methane and leuco base with indole or N,N-dimethylaniline in the presence of CuCl2.

The crystallographic study of 2,2’-((4-bromophenyl)methylene)bis(3-hydroxy-5,5-dimethylcyclohex-2-en-1-one) reveals that the compound crystallizes in the centrosymmetric space group $$P2_{1}/c$$ . In the solid state, the structure of the title compound exhibits two strong intramolecular $$\hbox {O}{-}\hbox {H}\cdots \hbox { O}$$ hydrogen bonding interactions. Further, molecules of the title compound are self-assembled by weak intermolecular $$\hbox {C}{-}\hbox {H}\cdots \hbox {O}, \pi \cdots \pi $$ and $$\hbox {H}\cdots \hbox { H}$$ and $$\hbox {C}{-}\hbox {H}\cdots \hbox { Br}$$ contacts. Various intermolecular interaction that exist in the crystal structure and their energetics are quantified using PIXEL, DFT and QTAIM analyses. Six different motifs are identified from the PIXEL calculation. Lattice energy calculation suggests that the dispersion energy has the highest contribution for the crystal formation. The relative contributions of various intermolecular contacts in the title compound and its closely related analogs are evaluated using Hirshfeld surface analysis and the decomposed fingerprint plots. The common packing features exist between the title compound and its related analogs are identified. The quantitative molecular electrostatic potential surface diagram depicts the potential binding sites which are in good agreement with the crystal structure of the title compound. The structures of title compound in gas and solvent phases are compared with the experimental structure and reveals that they are superimposed very well. The vibrational modes of the monomer and four most stabilized dimers are characterized using both the experimental and DFT calculations. The UV-Vis spectrum is calculated using time dependent-DFT (TD-DFT) method and compared with experimental spectrum. The results indicate that the calculated energy of absorbance and oscillator strength correlate well with the experimental data. SYNOPSIS. Synthesis and crystal structure analysis of 2,2’-((4-bromophenyl)methylene) bis(3-hydroxy-5,5-dimethylcyclohex-2-en-1-one) are reported. Molecules of this compound are self-assembled by intermolecular $$\hbox {C}{-}\hbox {H}\cdots \hbox {O}$$ , $$\pi \cdots \pi $$ and $$\hbox {H}\cdots \hbox { H}$$ and $$\hbox {C}{-}\hbox {H}\cdots \hbox { Br}$$ interactions. The relative contributions of various intermolecular interactions in the bromo derivative and its closely related analogs are quantified using theoretical approaches.

Oleic acid was identified to catalyse bis(indolyl)methane and densely functionalized 4H-chromene, spirooxindole and spiro[indoline-3,4′-pyrano[2,3-c]pyrazole] derivative synthesis in good to excellent yields. The synergy between Bronsted acidity and surfactant ability of naturally available oleic acid was exploited to carry out the aforementioned transformations.

Hyperbranched polyethylenimine (HPEI), an amine rich polymer, has been used as a colorimetric probe for selective sensing of multiple metal ions (Cu2+, Co2+ and Fe2+) with clearly distinguishable color in aqueous solution. The selective coordination of Cu2+ with the chelating amines of HPEI induced a visible color change from colorless to blue across a wide pH range (pH 4.0 to 10.0). Other metal ions did not show any significant color change. Interestingly, the addition of Co2+ and Fe2+ into HPEI in the presence of silver ions (Ag+) leads to the formation of strong yellow and brown colors, respectively. The control studies suggest that Co2+ and Fe2+ undergo oxidation and reduce the silver ions into silver nanoparticles (AgNPs). The strong surface plasmon resonance (SPR) vibration of the AgNPs was responsible for the yellow/brown color. UV-visible studies showed a strong absorption peak at 400 nm for Co2+ and a broad absorption with λmax at 420 nm for Fe2+. HR-TEM studies confirmed more uniform spherical AgNPs for Co2+ with HPEI–Ag+ and polydisperse AgNP aggregates for Fe2+. The limit of detection of the HPEI probe for Cu2+ is 0.25 μg L−1 and those of the HPEI–Ag+ probe for Co2+ and Fe2+ are 40 and 30 μg L−1, respectively. The practical application of the HPEI probe for selective sensing of multiple metal ions with distinguishable colors has been demonstrated on Whatman filter paper. Thus, simple commercially available HPEI has been successfully used for the selective colorimetric sensing of biologically important Cu2+, Co2+ and Fe2+ metal ions in aqueous medium.

Hyperbranched polyethylenimine derivatives were successfully employed as catalyst in the Henry reaction. The nitroalcohol products were obtained in excellent yields within short reaction times. A one-pot synthesis of β-nitrostyrenes was developed by using ZnCl2 along with hyperbranched polyethylenimine derivatives.

Three-component Betti reaction was carried out in the environmentally benign, inexpensive, non-toxic solvent glycerol. Even in the absence of a catalyst, the reaction went completion with an unprecedented high rate and the expected Betti bases were obtained in up to 91% yield. The reaction works well for representative cyclic, acyclic, aliphatic, and aromatic amines and aldehydes. A benzoxanthene was also prepared in 93% yield following the same methodology with 20 mol% methanesulfonic acid catalyst.

β-Amino esters were obtained in up to 78% yield with 72:28–96:4 diastereomeric ratios by the reaction of the chiral titanium enolate of menthyl esters, prepared using the TiCl4/Et3N reagent system with prochiral imines. A representative syn-β-amino ester derivative has been used for the resolution of racemic mandelic acid to obtain a sample with >99% ee in a single step. A representative syn-β-amino ester was converted to the corresponding N-deprotected amino ester using the Pd–C/HCOOH reagent system, and then to the corresponding β-amino acid using the glacial CH3COOH/HCl reagent system, and to the corresponding β-lactam derivative with partial epimerization by the reaction using C2H5MgBr.

The developed method allows for the preparation of functionalized 4H-chromene, spirooxindole, spiro[indoline-3,4′-pyrano[2,3-c]pyrazole], and bis(indolyl)methane derivatives.

The reactions of benzaldehyde imines and esters with the TiCl4/R3N reagent system give syn-β-amino esters as the major products in 38–87% yields.

Hyperbranched polyethylenimine derivatives were successfully employed as catalyst in the Henry reaction. The nitroalcohol products were obtained in excellent yields within short reaction times. A one-pot synthesis of β-nitrostyrenes was developed by using ZnCl2 along with hyperbranched polyethylenimine derivatives.

Glycerol is described as useful solvent for the rapid one-pot synthesis of Betti bases without the need for any catalyst.

Addition of titanium ester enolates to N-arylidene derivatives containing a (R)-α-methylbenzylamine moiety afforded (2S,3S,αR)-β-amino esters in 73–93% yields with 86:14 to 96:4 diastereomeric ratios.