Toward phenanthridin-2-ylidene: electrophilicity versus acidity in planar-constrained C-aryl iminium salts

A phenanthridinium salt was prepared in four steps, including an intramolecular CH-arylation and a hydride abstraction reaction. Treatment with sterically demanding bases does not lead to the corresponding carbene, but rather to addition products: the planar-constrained geometry significantly enhances the electrophilicity over the acidity of C-aryl iminium salts.     

单链四苯酚基卟啉在CTAB胶束微环境中的去质子化现象

叶绿素分子的光能转化功能的实现与其聚集状态、所处微环境性质及条件密切相关[1,2]．如何设计控制叶琳类分子在膜介质中的增溶位置，对于研究叶琳在膜体系中的跨膜电子传递、光能转化过程具有重要意义．本文研究了长链双亲卟啉──单链四苯酚基叶琳THPPH2在CTAB胶束中的去质子化，该过程能控制叶琳环在胶束中的增溶位置，使其由内核转移到胶束表面．1实验部分1·1仪器和测试条件岛津UV－240型紫外可见光谱仪（带有恒温夹套），狭缝宽2nm，石英池厚1cm，所用试剂皆为分析纯．UV光谱测试均在恒温条件下进行．1．2溶液的配制含一个十六…     

Synthesis and properties of fringelite D (1,3,4,6,8,10,11,13-octahydroxy-phenanthro[1,10,9,8,o,p,q,r,a]perylene-7,14-dione)

Summary Fringelite D was synthesized from 1,3,6,8-tetramethoxyanthracen-9-olvia two different efficient routes. The first one involved demethylation and subsequent dimerization. The other one started with dimerization to yield octamethylfringelite D and subsequent demethylation. The starting material was prepared in four steps from commercially available educts, the key step being a benzamideortho-lithiation. The spectroscopic properties of fringelite D were measured and are discussed. The dissociation, deprotonation, and protonation equilibria of fringelite D were characterized by their respectivepK values in ground and excited states and compared with those of hypericin. Homo- and heteroassociation properties of fringelite D were found to be similar to those of hypericin.

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Synthese und Eigenschaften von Fringelit D (1,3,4,6,8,10,11,13-Octahydroxy-phenanthro[1,10,9,8,o,p,q,r,a]perylen-7,14-dion)

Zusammenfassung Fringelit D wurde auf zwei effizienten Routen aus 1,3,6,8-Tetramethoxyanthracen-9-ol synthetisiert. Die erste umfaßt Demethylierung und anschließende Dimerisierung. Die andere beginnt mit der Dimerisierung zu Octamethylfringelit D und endet mit einer Demethylierung. Das Ausgangsmaterial wurde in vier Stufen aus kommerziell zugänglichen Edukten dargestellt; der Schlüsselschritt ist eineortho-Lithiierung eines Benzamids. Die spektroskopischen Eigenschaften von Fringelit D wurden gemessen und werden diskutiert. Die Dissoziations-, Deprotonierungs- und Protonierungsgleichgewichte wurden durch ihrepK-Werte in Grundzustand und angeregtem Zustand charakterisiert und mit jenen des Hypericins verglichen. Die Homo- und Hetero-assoziationseigenschaften von Fringelit D sind jenen des Hypericins ähnlich.

     

Isoprene-catalyzed lithiation of imidazole: synthesis of 2-(hydroxyalkyl)- and 2-(aminoalkyl)imidazoles

2-Lithioimidazole was prepared by means of a new protocol, which consists of a slight excess of lithium metal in the presence of a substoichiometric amount of isoprene (20 mol%) in THF at room temperature. By reacting this organolithium with carbonyl electrophiles 2-(hydroxyalkyl)imidazoles 3 were obtained, in good yields. As a result of the reaction of the mentioned lithium intermediate with imines 4, the corresponding 2-(aminoalkyl)imidazoles 5 were isolated in excellent yields.     

Structural aspects and electronic absorption of the hydroxyphenanthroperylene quinones fringelit D,hypericin, and stentorin

Summary PPP type semiempirical quantum chemical calculations of absorption spectra were performed for hypericin, fringelit D, stentorin, and their respective conformers, tautomers, and deprotonated species. The results agree with the experimental absorption spectra of hypericin, stentorin, and fringelit D, their deprotonated species, and the polarized absorption spectra of an ,-long chain appended hypericin derivative embedded in stretched polyethylene.

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Strukturelle Aspekte und elektronische Absorptionseigenschaften der Hydroxyphenanthroperylenchinone Fringelit D, Hypericin und Stentorin

Zusammenfassung Semiempirische quantenchemische Rechnungen (PPP-Typ) der Absorptions-spektren von Hypericin, Fringelit D, Stentorin und ihrer Konformeren, Tautomeren und deren Deprotonierungsprodukten wurden durchgeführt. Die Resultate stehen in Einklang mit den experimentellen Absorptionsspektren von Hypericin, Fringelit D, Stentorin, ihrer Deprotonierungsprodukte und dem polarisierten Absorptionsspektrum eines in gestrecktem Polyethylen eingebetteten ,-substituierten Hypericinderivates.

     

Spin-transition behaviour of transition metal complexes with 2,6-bis-(benzimidazol-2′-yl)-pyridine induced by deprotonation of the complex

Summary 2,6-bis-(Benzimidazol-2-yl)-pyridine (bzimpy = H₂ L) acts as a bidentate ligand when combining with transition metal ions. The complexes [M(bzimpy)₂](ClO₄)₂ (M = Fe²⁺, Mn²⁺, Zn²⁺, Co²⁺, and Ni²⁺) were obtained as solids. The protonation constants (logK) for the ligand and the complexes were evaluated in 30:70 (v/v) H₂O:EtOH at 293 K and at constant ionic strength of 0.12M KCl. Coordination of the ligand to the metal ions leads to an increase of acidity of the imino-hydrogen of the benzimidazole group of the ligand as a function of the complex stability. Deprotonation leads to a spin-state transition (intermediate spin-state low-spin) of the iron(II)-complex, followed by a shift of the metal-to-ligandcharge transfer band (MLCT) to lower energies (_max=563 to 580 nm). The d-d absorption bands are found to shift to higher energies and the low-spin isomer is favoured at room temperature. An opposite shift of theMLCT band (_max=563 to 557 nm) is observed when HClO₄ is added to the complex solution, rendering the high-spin state of the complex more favourable.On leave from the Chemistry Department, Jahangirnagar University, Dhaka, Bangladesh     

Comprehensive DFT and MO studies on glyoxilic acid oxime and related ions in gas phase and solution: Conformations,basicities and acidities

Density functional (BLYP, B3LYP and BHLYP) and highly correlated MP2 and CCSD(T) calculations have been performed to investigate conformers, energy barriers, intramolecular H-bond strength, gas-phase basicity and deprotonation energies of glyoxilic acid oxime (gao) and related ions in gas phase and in aqueous solution (SCRF-PCM method). BHLYP/6-311G(d,p) and B3LYP/6-31++G(d) predictions for the global minimum conformer of gao were consistent with experiment. BLYP level overestimated the H-bond and stabilized incorrectly the H-bonded conformer. The calculations in solution indicated destabilization of H-bonded conformers due to the small polarizability and weaken of the H-bond. The same global minimum structures in gas phase and aqueous solution were found for gao-neutral (ectt) and gao-dianion (e⁻²), whereas they were different for gao-anion because of the strong decrease of the conformational energies in solution. The global minimum structures of the neutral, anion and dianion of gao, obtained in solution, are in agreement with experiment. The gas-phase basicity (GB) and molecular electrostatic potential (MEP) calculations revealed the same sites for electrophilic attack, supported by the nature of HOMO: the carbonylic oxygen for the neutral, the carboxylic oxygen for the anion and the oxime nitrogen for the dianion. MEP results in gas phase and in solution suggested a region between the two atoms, but not on one atom in accordance with bidentate binding of gao ions to a metal. The BHLYP/6-31++G(d,p) molecular properties of gao were in best consistent with CCSD(T) results. The thermodynamical properties (GB and bond deprotonation energy) of gao were better estimated at B3LYP level.     

Conformational dependence of the intrinsic acidity of the aspartic acid residue sidechain in N-acetyl- -aspartic acid-N′-methylamide

The sidechain conformational potential energy hypersurfaces (PEHS) for the γ_L, β_L, α_L, and α_D backbone conformations of N-acetyl- -aspartate-N′-methylamide were generated. Of the 81 possible conformers initially expected for the aspartate residue, only seven were found after geometric optimizations at the B3LYP/6-31G(d) level of theory. No stable conformers could be located in the δ_L, _L, γ_D, δ_D, and _D backbone conformations. The ‘adiabatic’ deprotonation energies for the endo and exo forms of N-acetyl- -aspartic acid-N′-methylamide were calculated by comparing their optimized relative energies against those found for the seven stable conformers of N-acetyl- -aspartate-N′-methylamide. Sidechain conformational PEHSs were also generated for the estimation of ‘vertical’ deprotonation energies for both endo and exo forms of N-acetyl- -aspartic acid-N′-methylamide. All backbone–sidechain (N–H⁻O–C) and backbone–backbone (N–HO=C) hydrogen bond interactions were analyzed. A total of two backbone–backbone and four backbone–sidechain interactions were found for N-acetyl- -aspartate-N′-methylamide. The deprotonated sidechain of N-acetyl- -aspartate-N′-methylamide may allow the aspartyl residue to form strong hydrogen bond interactions (since it is negatively charged) which may be significant in such processes as protein–ligand recognition and ligand binding. As a primary example, the molecular geometry of the aspartyl residue may be important in peptide folding, such as that in the RGD tripeptide.     

Deprotonation of chloropyridines using lithium magnesates

4-Chloropyridine was deprotonated on treatment with 1/3 equiv of the highly coordinated magnesate Bu₃(TMP)MgLi₂ in THF at −10 °C, as evidenced by trapping with I₂. The use of Bu(TMP)₂MgLi in Et₂O allowed the reaction of 2-chloropyridine, giving the 3-functionalized derivative as the main product. Mixtures of 3- and 4-functionalized derivatives were obtained when 2,6-dichloropyridine was involved in the reaction. Performing the reaction on 3-chloropyridine with lithium magnesates in THF, either the 4,4′-dimer or the 4-iodo derivative was formed after quenching by I₂, the former using 1/3 equiv of Bu₂(TMP)MgLi and the latter using 1 equiv of (TMP)₃MgLi. Similar results were observed with 3,5-dichloropyridine, 2,5-dichloropyridine and 3-chloro-2-fluoropyridine. 1,2-Migration of the lithium arylmagnesate formed by deprotonation was proposed to justify the dimers formation.     

Convenient Method for the 3‐Functionalization of Isoindazoles

The C‐3 position of isoindazoles is readily functionalized by metalation with lithium diisopropylamide followed by reaction with a variety of electrophiles.