Polyphosphoric acid–zirconia pillared clay composite catalytic system for efficient multicomponent one pot synthesis of tetrahydropyridines under environmentally benign conditions

Synthesis, crystal structure, Hirshfeld surface analysis, DFT and NBO study of ethyl 1-(4-fluoro-phen-yl)-4-[(4-fluoro-phen-yl)amino]-2,6-diphenyl-1,2,5,6-tetra-hydro-pyridine-3-carboxyl-ate

The title com-pound, C32H28F2N2O2, a highly functionalized tetra-hydro-pyridine, was synthesized by a one-pot multi-com-ponent reaction of 4-fluoro-aniline, ethyl aceto-acetate and benzaldehyde at room temperature using sodium lauryl sulfate as a catalyst. The com-pound crystallizes with two mol-ecules in the asymmetric unit. The tetra-hydro-pyridine ring adopts a distorted boat conformation in both mol-ecules and the dihedral angles between the planes of the fluoro-substituted rings are 77.1 (6) and 77.3 (6)°. The amino group and carbonyl O atom are involved in an intra-molecular N-H⋯O hydrogen bond, thereby generating an S(6) ring motif. In the crystal, mol-ecules are linked by C-H⋯F hydrogen bonds forming a three-dimensional network and C-H⋯π inter-actions. A Hirshfeld surface analysis of the crystal structure indicates that the most important contributions to the crystal packing are from H⋯H (47.9%), C⋯H/H⋯C (30.7%) and F⋯H/H⋯F (12.4%) contacts. The optimized structure calculated using density functional theory (DFT) at the B3LYP/6-311+G(2d,p) level is compared with the experimentally determined molecular structure in the solid state. The HOMO-LUMO behaviour was used to determine the energy gap and the Natural Bond Orbital (NBO) analysis was done to study donor-acceptor interconnections.

Cu(I)-Induced Activation of Furan for Inverse Electron Demand ADAR with Alkenes toward Regioselective Synthesis of Tetrahydropyridine

The aza-Diels-Alder reaction of various alkenes and in situ formed 1-aza-1,3-dienes from the reaction of furan/pyrrole/thiophene and PhINTs for the regioselective synthesis of tetrahydropyridine (THP) derivatives was realized. The reaction was catalyzed by Tp^Me2Cu as a catalyst under very mild reaction conditions. Structurally different alkenes, along with an alkyne, have been utilized as dienophiles to afford a wide range of different THP derivatives up to 70% yield. The potential application of the envisaged method was also investigated by a gram-scale synthesis.

Conversion of Carbon Dots from Fluorescence to Ultralong Room-Temperature Phosphorescence by Heating for Security Applications

Stimuli-responsive optical materials have received tremendous interest in the last several decades due to their numerous promising applications. Here, fluorescence emissive polymer carbon dots (F-CDs), prepared with a simple heating treatment from ethylenediamine and phosphoric acid, are found to produce unexpected ultralong room-temperature phosphorescence (URTP), which lasts for about 10 s with a lifetime of 1.39 s. This is the first example to achieve the conversion of a fluorescence material to URTP by means of an external heating stimulus. Further investigations reveal that the doping of N and P elements and self-immobilization of the excited triplet species are likely mainly responsible for the observed URTP after the heating treatment, due to the facilitation of the intersystem crossing and formation of more compact cores for effective intraparticle hydrogen bonds, respectively. Importantly, this study also demonstrates the potential for aqueous dispersion of the F-CDs as an advanced security ink for information encryption and anticounterfeiting; this is a feature that has not been reported before. This study is believed to open possibilities to extend stimuli-responsive optical materials to rarely exploited phosphorescence-relevant systems and applications, and also to provide a novel strategy to easily prepare URTP materials.

Study of colloidal properties of natural and Al-pillared smectite and removal of copper ions from an aqueous solution

In this study, an Al-pillared smectite was synthesized and changes in its colloidal properties were investigated. The pillaring solution was prepared by mixing 0.4 mol L(-1) NaOH and 0.2 mol L(-1) AlCl3.6H2O solutions. Intercalated clays were heated to obtain the pillared clay, and X-ray diffractometry (XRD), X-ray fluorescence (XRF), Fourier transform infrared (FTIR) spectroscopy and N2 sorption/desorption isotherms analysis were done to characterize the changes in clay properties. Moreover, adsorption experiments were carried out in order to evaluate the capacity of the pillared clays to remove Cu2+ from an aqueous solution and to characterize the interaction between adsorbent and adsorbate. The results indicate that the natural clay has a basal spacing of 1.26 nm, whereas the pillared clays reached 1.78 nm (500°C) and 1.80 nm (350°C) after calcination. XRF analysis revealed an increase in the Al3+ in the pillared clay as compared to the natural clay. The surface area and pore volume (micro and mesoporous) were higher for the pillared clays. Experimental data from the adsorption experiment were fit to Langmuir and Freundlich and Temkin adsorption models, and the former one was the best fit (highest r2 value) for all the clays and lower standard deviation (Δg%) for the natural clay. On the other hand, the Temkin model exhibited Δg% value lower for the pillared clays. Thermodynamics parameters demonstrate that the Cu2+ adsorption process is spontaneous for all the clays, but with higher values for the pillared materials. In addition, application of the Dubinin-Radushkevich model revealed that the bond between the metal and the clay are weak, characterizing a physisorption.