A Fragment Based Approach toward Thia[<i>n</i>]helicenes

The synthesis of [9]- and [11]thiahelicenes, as well as the preparation of lower homologues such as [5]-, [6]-, and [7]thiahelicenes is reported. Efficient palladium catalyzed coupling reactions were employed. Triorganoindium derivatives were selectively mono-cross-coupled with <i>N</i>-methyl-3,4-dibromomaleimide followed by Stille coupling with the readily available building block naphthodithiophene. Oxidative photocyclization of the conjugated precursors using visible light was employed to synthesize a series of thia[<i>n</i>]helicenes. This modular synthetic methodology is independent of the length of the helical backbone

Solvent Extraction of Scandium(III) by an Aqueous Biphasic System with a Nonfluorinated Functionalized Ionic Liquid

The use of ionic liquids (ILs) as solvents for extraction of metals is a promising development in separation science and technology; yet, the viscosities of ionic liquids (ILs) can be so high that long reaction times are required to reach the equilibrium state. An aqueous biphasic system (ABS) consisting of the nonfluorinated carboxyl-functionalized phosphonium IL [P₄₄₄C₁COOH]Cl and a 16 wt % NaCl solution is described. The IL-rich phase of the aqueous biphasic system has a very low viscosity, in comparison to the pure IL [P₄₄₄C₁COOH]­Cl. This system has excellent extraction properties for scandium. Different extraction parameters were investigated, including contact time and metal loading. The influence of the pH on the solubility of the IL cation in the water-rich phase was determined via quantitative ¹H NMR. The stripping of scandium with oxalic acid from the IL phase was also investigated. A plausible extraction mechanism is proposed where three IL cations are deprotonated to form zwitterionic compounds that can coordinate scandium­(III) ions

A One-Pot Procedure for the Synthesis of “Click-Ready” Triazoles from Ketones

A practical, straightforward, and highly regioselective Zn­(OAc)₂-mediated method toward propargyl triazoles has been developed for the first time from commercially available enolizable ketones and propargyl amine. Postfunctionalization of this triazole leads to unique N- and C-linked bis-triazoles in excellent yields

Three-Step Synthetic Pathway toward Fully Decorated [1,2,3]Triazolo[4,5‑<i>d</i>]pyrimidine (8-Azapurine) Derivatives

[1,2,3]Triazolo[4,5-d]pyrimidines (8-azapurines) are known bioisosteres of the purine nucleus. A step-efficient synthesis of 8-azapurines, in particular 6-alkyl derivatives, is currently unavailable. This work focuses on a three-step synthetic pathway for the synthesis of fully decorated 8-azapurines, with special attention on 6-alkyl-8-azapurines. A diverse library of 8-azapurines was obtained starting from various alkynes, azides, and amidines, involving interrupted CuAAC, oxidation, and cyclization reactions. Additionally, postfunctionalization reactions were demonstrated for a selected number of substrates

Selenium–Platinum Coordination Dendrimers with Controlled Anti-Cancer Activity

Dendrimers are considered as good vectors for drug delivery in cancer treatment. However, most anticancer drugs are conjugated to the peripheral surface of dendrimers, sacrificing the advantages of monodispersity and stability belonging to dendrimers. Furthermore, dendrimers in current studies of cancer treatment are mostly used as vectors for drugs, whereas the anticancer activity of dendrimers on their own is less studied. Here we have prepared monodisperse selenium–platinum coordination dendrimers with a selenium–platinum core buried inside. Structures of the dendrimers were determined by various characterizations. The coordination dendrimers showed controlled anticancer activity by themselves, without loading additional drugs. The in vivo study further demonstrated their anticancer activity and low toxicity to normal tissues

A Fragment-Based Approach toward Substituted Trioxa[7]helicenes

A series of novel substituted trioxa[7]helicenes have been successfully prepared by a one-pot palladium catalyzed C–H arylation reaction starting from readily prepared dibenzofuran fragments. The dinitro-substituted helicene was analyzed by X-ray crystallography revealing the occurrence of two distinct enantiomers in the asymmetric unit, which forms interesting supramolecular motifs in the crystal, based on weak H-bonding interactions

Three-Step Synthetic Pathway toward Fully Decorated [1,2,3]Triazolo[4,5‑<i>d</i>]pyrimidine (8-Azapurine) Derivatives

[1,2,3]Triazolo[4,5-d]pyrimidines (8-azapurines) are known bioisosteres of the purine nucleus. A step-efficient synthesis of 8-azapurines, in particular 6-alkyl derivatives, is currently unavailable. This work focuses on a three-step synthetic pathway for the synthesis of fully decorated 8-azapurines, with special attention on 6-alkyl-8-azapurines. A diverse library of 8-azapurines was obtained starting from various alkynes, azides, and amidines, involving interrupted CuAAC, oxidation, and cyclization reactions. Additionally, postfunctionalization reactions were demonstrated for a selected number of substrates

A Fragment-Based Approach toward Substituted Trioxa[7]helicenes

A series of novel substituted trioxa[7]helicenes have been successfully prepared by a one-pot palladium catalyzed C–H arylation reaction starting from readily prepared dibenzofuran fragments. The dinitro-substituted helicene was analyzed by X-ray crystallography revealing the occurrence of two distinct enantiomers in the asymmetric unit, which forms interesting supramolecular motifs in the crystal, based on weak H-bonding interactions

Oxidative Transformation to Naphthodithiophene and Thia[7]helicenes by Intramolecular Scholl Reaction of Substituted 1,2-Bis(2-thienyl)benzene Precursors

We present here a strategy to synthesize a variety of substituted naphthodithiophene building blocks through DDQ/acid-mediated oxidative cyclizations. The versatility of the Scholl reaction using the DDQ/acid system was demonstrated by the preparation of a novel substituted tetrathia[7]­helicene where three new C–C bonds were formed in a one-pot procedure. The new DDQ/acid method was compared to the known strategies such as FeCl₃ oxidation and oxidative photocyclization. By protecting the 1,2-bis­(2-thienyl)­benzene precursors, it is possible to direct the intermediates to controlled cyclization and effectively suppressing the polymerization. The highly reactive α-position of the terminal thiophenes can allow for further functionalization. The efficient preparation of a variety of naphthodithiophene building blocks, the extension to a nonphotochemical synthesis of [<i>n</i>]­helicenes, and the ease of isolation of the products are arguments for the use of DDQ/acid system for this Scholl reaction

Synthesis of Poly‑<i>p</i>‑phenylene Terephthalamide (PPTA) in Ionic Liquids

Several ionic liquids (ILs) were tested for their suitability to synthesize the aramid polymer poly-<i>p</i>-phenylene terephthalamide (PPTA) in an attempt to diminish the dependence on the toxic <i>N</i>-methylpyrrolidone (NMP) that is currently used in industry. The room-temperature IL 3-methyl-1-octylimidazolium chloride ([C₈MIM]­[Cl]) showed the highest promise as, with this medium, the polycondensation reaction proceeds with a mechanism similar to how it occurs in the solvent mixture of NMP with CaCl₂. With this IL, PPTA polymer with an inherent viscosity of 1.95 dL/g was obtained in a low-temperature polycondensation reaction. This is the highest reported molecular mass of PPTA to date that was obtained by polymerization in an ionic liquid. An extended X-ray absorption fine structure (EXAFS) and solid-state NMR spectroscopic study showed that [C₈MIM]­[Cl] and the current industrial solvent of NMP and CaCl₂ show similar characteristics when it comes to the synthesis of PPTA