Modular access to heterocycles: methyl 3-aminobenzo[<Emphasis Type="Italic">b</Emphasis>]thiophene-2-carboxylate–thiourea linkage or pyrimidine-4-one-2-thione formation

Abstract  Modular conditions for the formation of thioureas or pyrimidine-4-one-2-thiones connected to the benzo[b]thiophene, benzene and indole structures were performed. A benzo[b]thiophene isothiocyanate derivative was used as a model to study the condensation with simple aromatic amines and amino-l-sorbose derivative. The construction of pyrimidine-4-one-2-thiones using basic conditions afforded efficiently new heterocyclic aromatics, which were further transformed using the alkylated sulfur as a leaving group in palladium-catalyzed cross-coupling reactions. Graphical abstract        

Spontaneous Bi-modification of polycrystalline Pt electrode: fabrication, characterization, and performance in formic acid electrooxidation

Spontaneous modification of polycrystalline Pt by irreversibly adsorbed bismuth was performed in BiCl₃ solution in concentrated hydrochloric acid under open-circuit conditions. After spontaneous modification, followed by extensive rinsing with water and drying, the surface was characterized using X-ray photoelectron spectroscopy and electrochemistry. Bi-oxy(chloride), oxide species, and metallic Bi were found at a submonolayer coverage on the Pt surface after spontaneous modification. The electrochemical response of Bi-modified polycrystalline Pt electrode in sulfuric acid solution exhibits a complex multi-peak feature, which is resulting in about constant redox charge (Bi species coverage) in the potential region from 0 to 0.9 V (vs. a standard hydrogen electrode). The spontaneously Bi-modified Pt catalyst in model studies exhibits a superior activity towards formic acid oxidation at fuel cell anode relevant potentials. The catalytic effect of bismuth oxy-species is explained in terms of both inhibition of CO_ad formation and oxidation of CO_ad in reaction with Bi-oxy-species.     

Colorimetric Cyanide Chemosensor Based on 1′,3,3′,4-Tetrahydrospiro[chromene-2,2′-indole]

A new class of chemosensors based on the 1′,3,3′,4-tetrahydrospiro[chromene-2,2′-indole] ring system, which detects cyanide with high specificity, is described. These chemosensors show a distinct color change when treated with cyanide in acetonitrile solution buffered with sodium phosphate, and this procedure is not affected by the presence of other common anions. The chemisensors exhibit high sensitivity to low concentrations of cyanide, meeting the European Union water quality control criterion of sensitivity below 0.05 mg L⁻¹, and show a very fast response within tens of seconds. The mechanism for detection is rationalized by the nucleophilic substitution of the phenolic oxygen atom at the indoline C-2 atom by the cyanide anion to form a stable indolylnitrile adduct and to generate the colored 4-nitrophenolate chromophore. These chemosensors can be synthesized by a simple procedure from commercially available starting materials.     

Synthesis and Characterization of Novel Methyl (3)5-(N-Boc-piperidinyl)-1H-pyrazole-4-carboxylates

Series of methyl 3- and 5-(N-Boc-piperidinyl)-1H-pyrazole-4-carboxylates were developed and regioselectively synthesized as novel heterocyclic amino acids in their N-Boc protected ester form for achiral and chiral building blocks. In the first stage of the synthesis, piperidine-4-carboxylic and (R)- and (S)-piperidine-3-carboxylic acids were converted to the corresponding β-keto esters, which were then treated with N,N-dimethylformamide dimethyl acetal. The subsequent reaction of β-enamine diketones with various N-mono-substituted hydrazines afforded the target 5-(N-Boc-piperidinyl)-1H-pyrazole-4-carboxylates as major products, and tautomeric NH-pyrazoles prepared from hydrazine hydrate were further N-alkylated with alkyl halides to give 3-(N-Boc-piperidinyl)-1H-pyrazole-4-carboxylates. The structures of the novel heterocyclic compounds were confirmed by ¹H-, ¹³C-, and ¹⁵N-NMR spectroscopy and HRMS investigation.     

Copper-catalyzed S-arylation of Furanose-Fused Oxazolidine-2-thiones

The 1,3-oxazolidine-2-thiones (OZTs) are important chiral molecules, especially in asymmetric synthesis. These compounds serve as important active units in biologically active compounds. Herein, carbohydrate anchored OZTs were explored to develop a copper-catalyzed C-S bond formation with aryl iodides. Chemoselective S-arylation was observed, with copper iodide and dimethylethylenediamine (DMEDA) as the best ligand in dioxane at 60–90 °C. The corresponding chiral oxazolines were obtained in reasonable to good yields under relatively mild reaction conditions. This approach is cheap, as using one of the cheapest transition metals, a simple protocol and various functional group tolerance make it a valuable strategy for getting S-substituted furanose-fused OZT. The structures of the novel carbohydrates were confirmed by NMR spectroscopy and an HRMS analysis.     

Mild Copper-Catalyzed,l-Proline-Promoted Cross-Coupling of Methyl 3-Amino-1-benzothiophene-2-carboxylate

Cu-catalyzed N-arylation is a useful tool for the chemical modification of aromatic heterocycles. Herein, an efficient carbon–nitrogen cross-coupling of methyl 3-amino-1-benzothiophene-2-carboxylate with a range of (hetero)aryl iodides using CuI, l-proline and Cs₂CO₃ in dioxane at moderate temperature is described. The procedure is an extremely general, relatively cheap, and experimentally simple way to afford the N-substituted products in moderate to high yields. The structures of the new heterocyclic compounds were confirmed by NMR spectroscopy and HRMS investigation.