Photoredox approach to N-Acyl-N'-aryl-N,N'-aminals using enamides and their conversion to γ-lactams

A photoredox catalytic approach to synthetically valuable N-acyl-N'-aryl-N,N'-aminals is described. This method uses the addition of a radical precursor to enamides, with subsequent interception of the cationic iminium intermediate with an arylamine. The reaction has been shown to be compatible with electron-rich and electron-deficient arylamines, and moderate to good levels of diastereoselectivity can be attained using a chiral enamide. Furthermore, the N-acyl-N'-aryl-N,N'-aminal reaction products can be readily cyclized, providing a novel synthetic route to valuable γ-lactams

Isolation and structure determination of the first example of the azeto[2,3-c]quinolizinedione ring system

An unexpected azeto[2,3-c]quinolizinedione has been isolated during synthetic studies on the base catalyzed condensation of ethyl 6-methylpyridin-2(1H)-on-1-ylacetate with benzil. Closure of a fused four-membered azetidinone ring occurred when potassium hexamethyldisilazide was employed as the base. The structure of the product was confirmed by synchrotron X-ray crystallography. A possible mechanism for the formation of the product is considered

The selective mono and difunctionalization of carbocyclic cleft molecules with pyridyl groups and X-ray crystallographic analysis

The diesterification and selective mono and dialkylation of carbocyclic analogues of Tröger’s base with pyridyl groups has been achieved in high yield and good selectivity giving access to a novel range of cleft molecules capable of binding events. Reaction conditions for the selective functionalization of this carbocyclic cleft molecule are discussed as well as the solid state structures of these newly synthesized ligands

Novel fluorinated benzimidazole-based scaffolds and their anticancer activity in vitro

A small library of twelve, structurally diverse, fluoroaryl benzimidazoles was prepared using a simple synthetic strategy employing SNAr reactions. This allowed rapid assembly of heterocyclic structures containing linked and tethered fluoroaryl benzimidazoles. X-ray crystal structures of seven compounds were obtained including those of two macrocyclic compounds containing 21- and 24-membered rings. Three tethered fluoroaryl benzimidazole derivatives demonstrated micromolar inhibition against K-562 and MCF-7 cell lines. These compounds, in addition to 1-tetrafluoropyrid-4-yl-2-tetrafluoropyrid-4-ylsulfanyl-1H-benzimidazole, also demonstrated micromolar inhibition against G361 and HOS cell lines. Two of the compounds were found to activate caspases leading to apoptosis

Multiple photoluminescence from pyrene-fused hexaarylbenzenes with aggregation enhanced emission features

Multiple photoluminescence, involved in monomer emission, excimer emission and charge transfer emission origin from new pyrene-fused hexaarylbenzenes (HAB) compounds were observed, which were designed and synthesized (in high yield) via the Diels-Alder reaction of bis(2-tert-butylpyren-6-yl)acetylene and tetraphenylcyclopentadienone. Although the distinction of between two molecules arises only from the geometrical position of one of the pyrenes, the NMR spectra, the crystal packing and the physicochemical properties of these pyrene-based HAB hybrids are distinctly different both in their solution state and in aggregation-state. The X-ray diffraction analysis clearly indicated that the pyrene moieties in this system would form different crystal packing in crystal state that can induce a fantastic multiple photoluminescence phenomenon

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Structural and Thermodynamic Study of the Complexes of Nd(III) with <i>N</i>,<i>N</i>,<i>N</i>′,<i>N</i>′‑Tetramethyl-3-oxa-glutaramide and the Acid Analogues

The thermodynamics of Nd­(III) complexes with <i>N</i>,<i>N</i>,<i>N</i>′,<i>N</i>′-tetramethyl-3-oxa-glutaramide (TMOGA, L^I), <i>N</i>,<i>N</i>-dimethyl-3-oxa-glutaramic acid (DMOGA, HL^II), and oxydiacetic acid (ODA, H₂L^III) in aqueous solutions was studied. Stability constants, enthalpies, and entropies of complexation were determined by spectrophotometry, potentiometry, and calorimetry. The stability constants of corresponding Nd­(III) complexes decrease in the following order: Nd­(III)/L^III > Nd­(III)/L^II > Nd­(III)/L^I. For all complexes, the enthalpies of complexation are negative and the entropies of complexation are positive, indicating that the complexation is driven by both enthalpy and entropy. Furthermore, from L^III to L^II, and to L^I, the enthalpy of complexation becomes more exothermic and the entropy of complexation less positive, suggesting that the substitution of a carboxylate group with an amide group on the ligands enhances the enthalpy-driven force but weakens the entropy-driven force of the complexation with Nd­(III). Crystal structures of three 1:3 Nd­(III) complexes, Nd­(L^I)₃(ClO₄)₃ (<b>I</b>), Nd­(L^I)₃(NO₃)₃(H₂O)₂ (<b>II</b>), and Nd­(L^II)₃(H₂O)_7.5 (<b>III</b>), were determined by single-crystal X-ray diffraction and compared with the structure of a 1:3 Nd­(III)/L^III complex in the literature, Na₃NdL^III₃(NaClO₄)₂(H₂O)₆ (<b>I</b><b>V</b>). In all four structures, the ligands are tridentate and Nd­(III) is nine-coordinated with similar distorted tricapped trigonal prism geometry by three ether oxygen atoms capped on the three faces of the prism, and six oxygen atoms from the ketone group or carboxyl group at the corners. The absorption spectra of Nd­(III) in solutions showed very similar patterns as Nd­(III) formed successive 1:1, 1:2, and 1:3 complexes with L^I, L^II, and L^III, respectively, implying that the Nd­(III) complexes with the three ligands have similar coordination geometries in aqueous solutions, as observed in the solids

Structural and Thermodynamic Study of the Complexes of Nd(III) with <i>N</i>,<i>N</i>,<i>N</i>′,<i>N</i>′‑Tetramethyl-3-oxa-glutaramide and the Acid Analogues

The thermodynamics of Nd­(III) complexes with <i>N</i>,<i>N</i>,<i>N</i>′,<i>N</i>′-tetramethyl-3-oxa-glutaramide (TMOGA, L^I), <i>N</i>,<i>N</i>-dimethyl-3-oxa-glutaramic acid (DMOGA, HL^II), and oxydiacetic acid (ODA, H₂L^III) in aqueous solutions was studied. Stability constants, enthalpies, and entropies of complexation were determined by spectrophotometry, potentiometry, and calorimetry. The stability constants of corresponding Nd­(III) complexes decrease in the following order: Nd­(III)/L^III > Nd­(III)/L^II > Nd­(III)/L^I. For all complexes, the enthalpies of complexation are negative and the entropies of complexation are positive, indicating that the complexation is driven by both enthalpy and entropy. Furthermore, from L^III to L^II, and to L^I, the enthalpy of complexation becomes more exothermic and the entropy of complexation less positive, suggesting that the substitution of a carboxylate group with an amide group on the ligands enhances the enthalpy-driven force but weakens the entropy-driven force of the complexation with Nd­(III). Crystal structures of three 1:3 Nd­(III) complexes, Nd­(L^I)₃(ClO₄)₃ (<b>I</b>), Nd­(L^I)₃(NO₃)₃(H₂O)₂ (<b>II</b>), and Nd­(L^II)₃(H₂O)_7.5 (<b>III</b>), were determined by single-crystal X-ray diffraction and compared with the structure of a 1:3 Nd­(III)/L^III complex in the literature, Na₃NdL^III₃(NaClO₄)₂(H₂O)₆ (<b>I</b><b>V</b>). In all four structures, the ligands are tridentate and Nd­(III) is nine-coordinated with similar distorted tricapped trigonal prism geometry by three ether oxygen atoms capped on the three faces of the prism, and six oxygen atoms from the ketone group or carboxyl group at the corners. The absorption spectra of Nd­(III) in solutions showed very similar patterns as Nd­(III) formed successive 1:1, 1:2, and 1:3 complexes with L^I, L^II, and L^III, respectively, implying that the Nd­(III) complexes with the three ligands have similar coordination geometries in aqueous solutions, as observed in the solids

Structural and Thermodynamic Study of the Complexes of Nd(III) with <i>N</i>,<i>N</i>,<i>N</i>′,<i>N</i>′‑Tetramethyl-3-oxa-glutaramide and the Acid Analogues

The thermodynamics of Nd­(III) complexes with <i>N</i>,<i>N</i>,<i>N</i>′,<i>N</i>′-tetramethyl-3-oxa-glutaramide (TMOGA, L^I), <i>N</i>,<i>N</i>-dimethyl-3-oxa-glutaramic acid (DMOGA, HL^II), and oxydiacetic acid (ODA, H₂L^III) in aqueous solutions was studied. Stability constants, enthalpies, and entropies of complexation were determined by spectrophotometry, potentiometry, and calorimetry. The stability constants of corresponding Nd­(III) complexes decrease in the following order: Nd­(III)/L^III > Nd­(III)/L^II > Nd­(III)/L^I. For all complexes, the enthalpies of complexation are negative and the entropies of complexation are positive, indicating that the complexation is driven by both enthalpy and entropy. Furthermore, from L^III to L^II, and to L^I, the enthalpy of complexation becomes more exothermic and the entropy of complexation less positive, suggesting that the substitution of a carboxylate group with an amide group on the ligands enhances the enthalpy-driven force but weakens the entropy-driven force of the complexation with Nd­(III). Crystal structures of three 1:3 Nd­(III) complexes, Nd­(L^I)₃(ClO₄)₃ (<b>I</b>), Nd­(L^I)₃(NO₃)₃(H₂O)₂ (<b>II</b>), and Nd­(L^II)₃(H₂O)_7.5 (<b>III</b>), were determined by single-crystal X-ray diffraction and compared with the structure of a 1:3 Nd­(III)/L^III complex in the literature, Na₃NdL^III₃(NaClO₄)₂(H₂O)₆ (<b>I</b><b>V</b>). In all four structures, the ligands are tridentate and Nd­(III) is nine-coordinated with similar distorted tricapped trigonal prism geometry by three ether oxygen atoms capped on the three faces of the prism, and six oxygen atoms from the ketone group or carboxyl group at the corners. The absorption spectra of Nd­(III) in solutions showed very similar patterns as Nd­(III) formed successive 1:1, 1:2, and 1:3 complexes with L^I, L^II, and L^III, respectively, implying that the Nd­(III) complexes with the three ligands have similar coordination geometries in aqueous solutions, as observed in the solids

Models for Copper Dynamic Behavior in Doped Cadmium dl-Histidine Crystals: Electron Paramagnetic Resonance and Crystallographic Analysis

Electron paramagnetic resonance and crystallographic studies of copper-doped cadmium dl-histidine, abbreviated as CdDLHis, were undertaken to gain further understanding on the relationship between site structure and dynamic behavior in biological model complexes. X-ray diffraction measurements determined the crystal structure of CdDLHis at 100 and 298 K. CdDLHis crystallizes in the monoclinic space group <i>P</i>2₁/<i>c</i> with two cadmium complexes per asymmetric unit. In each complex, the Cd is hexacoordinated to two histidine molecules. Both histidines are l in one complex and d in the other. Additionally, each complex contains multiple waters of varying disorder. Single crystal EPR spectroscopic splitting (<b>g</b>) and copper hyperfine (<b>A</b>^<b>Cu</b>) tensors at room temperature (principal values: <b>g</b> = 2.249, 2.089, 2.050; <b>A</b>^<b>Cu</b> = −453, −30.5, −0.08 MHz) were determined from rotational experiments. Alignments of the tensor directions with the host structure were used to position the copper unpaired d_{<i>x</i>²‑<i>y</i>²} orbital in an approximate plane made by four proposed ligand atoms: the <i>N</i>-imidazole and <i>N</i>-amino of one histidine, and the <i>N</i>-amino and <i>O</i>-carboxyl of the other. Each complex has two such planes related by noncrystallographic symmetry, which make an angle of 65° and have a 1.56 Å distance between their midpoints. These findings are consistent with three interpretations that can adequately explain previous temperature-dependent EPR powder spectra of this system: (1) a local structural distortion (static strain) at the copper site has a temperature dependence significant enough to affect the EPR pattern, (2) the copper can hop between the two sites in each complex at high temperature, and (3) there exists a dynamic Jahn–Teller effect involving the copper ligands