Synthesis and Self‐Association of Double‐Helical AADD Arrays

The design and syntheses of four self‐complementary oligomers that contain an underlying AADD hydrogen bond sequence are presented, and their self‐association was examined in the solution and solid state. The molecular recognition between the two strands is highly sensitive to substitutions of their component heterocycles. Substitution with electron‐donating and ‐withdrawing groups and the influence of preorganization has a large effect on the overall stabilities of the complexes studied. In particular, a wide range (>10⁵ M ^?1) of stabilities with respect to substitutions at various positions in the AADD oligomers was demonstrated. In the most extreme case, the dimerization constant measured (K_dimer≥4.5×10⁷ M ^?1) is comparable to the most stable homodimers of neutral AADD arrays reported to date.     

Nuclear Versus Side-Chain Bromination of 4-Methoxy Toluene by an Electrochemical Method

The electrochemical bromination of 4-methoxy toluene by two-phase electrolysis yields 3-bromo 4-methoxy toluene at first, which subsequently undergoes side-chain bromination to give 3-bromo 4-methoxy benzyl bromide as a final product in 86% yield. The two-phase electrolysis consists of 25–50% NaBr as aqueous electrolyte and CHCl₃ containing aromatic compound as organic phase. The reaction temperature is maintained at 10–25 °C. The probable orientation of bromine atom in an alkyl aromatic compound (nuclear versus side chain) is explained from the experimental result.     

Copper(II)-catalyzed direct thiolation of C–H bonds in aromatic amides with aryl and aliphatic thiols

An efficient approach for Cu-catalyzed thiolation of C_sp2–H bonds of directing-group-containing aromatic amides with 1°, 2°, and 3° aliphatic thiols and thiophenols has been developed. This method shows excellent functional group tolerance and provides a straightforward way for the preparation of aryl thioethers.     

The Family of Ferrocene‐Stabilized Silylium Ions: Synthesis, 29Si NMR Characterization,Lewis Acidity,Substituent Scrambling,and Quantum‐Chemical Analyses

The purpose of this systematic experimental and theoretical study is to deeply understand the unique bonding situation in ferrocene‐stabilized silylium ions as a function of the substituents at the silicon atom and to learn about the structure parameters that determine the ²⁹Si NMR chemical shift and electrophilicity of these strong Lewis acids. For this, ten new members of the family of ferrocene‐stabilized silicon cations were prepared by a hydride abstraction reaction from silanes with the trityl cation and characterized by multinuclear ¹H and ²⁹Si NMR spectroscopy. A closer look at the NMR spectra revealed that additional minor sets of signals were not impurities but silylium ions with substitution patterns different from that of the initially formed cation. Careful assignment of these signals furnished experimental proof that sterically less hindered silylium ions are capable of exchanging substituents with unreacted silane precursors. Density functional theory calculations provided mechanistic insight into that substituent transfer in which the migrating group is exchanged between two silicon fragments in a concerted process involving a ferrocene‐bridged intermediate. Moreover, the quantum‐chemical analysis of the ²⁹Si NMR chemical shifts revealed a linear relationship between δ(²⁹Si) values and the Fe???Si distance for subsets of silicon cations. An electron localization function and electron localizability indicator analysis shows a three‐center two‐electron bonding attractor between the iron, silicon, and C′_ipso atoms, clearly distinguishing the silicon cations from the corresponding carbenium ions and boranes. Correlations between ²⁹Si NMR chemical shifts and Lewis acidity, evaluated in terms of fluoride ion affinities, are seen only for subsets of silylium ions, sometimes with non‐intuitive trends, indicating a complicated interplay of steric and electronic effects on the degree of the Fe???Si interaction.     

Convenient Synthesis of 14‐Aryl‐14‐H‐dibenzo[a,j]xanthenes Catalyzed by Acyclic Brønsted Acidic Ionic Liquid [H—NMP]+[HSO4]− under Microwave Irradiation

Efficient method for direct preparation of 14‐aryl‐14‐H‐dibenzo[a,j]xanthenes through condensation of β‐naphthol with various aromatic aldehydes in the presence of the catalytic amount of [H—NMP]⁺[HSO₄]^? under microwave irradiation was described. This method has the advantages such as; very easy reaction workup, absolute separation of catalyst from the reaction mixture and smooth recyclability of catalyst. In this reaction 14‐aryl‐14‐H‐dibenzo[a,j]xanthenes were obtained as desired products in excellent yields and short reaction times via green and one‐pot procedure.     

REGIOSELECTIVE NITRATION OF 1-ACYL-4-METHOXYINDOLINES LEADS TO EFFICIENT SYNTHESIS OF A PHOTOLABILE l-GLUTAMATE PRECURSOR

ABSTRACT

Different nitrating reagents give different ratios of 5- and 7-nitro isomers of the title indolines. The best ratio of the 7-nitro isomer was obtained with claycop–acetic anhydride, and these conditions were particularly useful for preparation of a photolabile l-glutamate derivative.     

Synthesis,Structures, and Luminescent Properties of two 3, 5‐Dimethyl‐1‐H‐1, 2,4‐triazole‐Based Zinc Metal‐Organic Frameworks with Aromatic Carboxylate as Coligand

Two metal‐organic frameworks, [Zn(dmtrz)(btrc)_1/3]_n ( 1 ) and [Zn₂(dmtrz)₂(btec)(H₂O)₂]_n ( 2 ) (dmtrz = 3, 5‐dimethyl‐1‐H‐1, 2,4‐triazole, btrc = 1, 3,5‐benzenetricarboxylate, btec = 1, 2,4, 5‐benzenetetracarboxylate), were synthesized by hydrothermal reaction. The crystal structure analysis reveals that compound 1 is a dense 3D framework with Schläfli symbols of {4³}₂{4⁶ · 6⁶ · 8³}₃, which is a loh1 structure. Compound 2 is a 2D network. In addition, the photoluminescence of two compounds were studied in solid state at room temperature, together with their thermal analysis.     

A Practical Knoevenagel Condensation Catalyzed by PEG400 and Anhydrous K2CO3 Without Solvent

Abstract

Knoevenagel condensation of aromatic aldehydes with active methylene compounds under solvent‐free conditions to synthesize arylidene compounds in good to excellent yields using powdered anhydrous K₂CO₃ and PEG400 as catalysts has been described.