Facile microwave-assisted synthesis of substituted benzofuran derivatives

A series of benzofuran derivatives have been synthesized by use of a microwave-assisted process. Substituted or unsubstituted ο-hydroxyacetophenone and salicylaldehyde reacted with ethyl bromoacetate, ω-bromoacetophenone, or chloroacetone under the action of potassium carbonate in DMF to yield substituted benzofuran derivatives. Compared with conventional heating, this microwave-assisted synthetic process has the advantages of more convenient operation, shorter reaction time, and higher yield.     

Facile microwave-assisted synthesis of thioformamides from isocyanides and carbon disulfide

A new, fast, solvent-free and efficient method is provided to prepare thioformamides by reacting isocyanides derivatives, carbon disulfide and benzylamine under microwave irradiation.     

Synthesis and rearrangement of diphosphorus analogues of amidinium salts

Transient diphosphinocarbocations IIP are generated either by addition of phosphenium salts to the stable [bis(diisopropylamino)phosphino](silyl)carbene or by chloride abstraction from C-phosphino-P-chloro phosphorus ylides. In contrast to their nitrogen anlogues (amidinium salts) IIN, which feature a planar 3-center-4p-electron system, calculations show that IIP should exist as IIPb, in which one phosphorus is planar, while the other remains pyramidal. With small substituents at phosphorus, derivatives of type IIP rearrange by a 1,3-shift of a phosphorus substituent to the other phosphorus center to give C-phosphoniophosphaalkenes. When bulky substituents are present at phosphorus, derivatives IIP undergo ring closure, giving rise to the corresponding cyclic valence isomers IIIP, in which the carbon atom bears a negative charge. Diphosphinocarbocations IIP can be trapped by acetonitrile giving regioselectively the corresponding [2+3] cycloadduct.     

Facile solid-phase synthesis of cyclic decapeptide antibiotic streptocidins A-D

Total synthesis of decapeptide antibiotics streptocidins A-D from Streptomyces sp. Tü 6071 was accomplished for the first time by solid-phase peptide synthesis followed by traceless cyclization of the activated linear precursors, without protection of nucleophilic side chain. Synthetic products were equally active as the natural products isolated from the bacterial source and found to possess similar bacterial selectivity as other members in the amphipathic antimicrobial cyclic decapeptide family.     

Facile microwave-assisted synthesis of 9,10-dihydro-9,10-ethanoanthracene-11-carboxylic acid methyl ester

A facile, high yielding synthesis of 9,10-dihydro-9,10-ethano- anthracene-11- carboxylic acid methyl ester using a modified commercial domestic microwave oven is reported.     

Facile synthesis of N,N'-ethylenebisthiazolium salts: precursors of dithiadiazafulvalenes

Bis-thiazolium salts, precursors of dithiadiazafulvalene (DTDAF), have been prepared. Electrochemical investigations have been carried out on these salts in order to determine the redox behavior of DTDAF. These bis-thiazolium salts undergo intramolecular coupling, either chemically or electrochemically, to afford N,N'-ethylene-bridged DTDAF.     

Facile synthesis of N-alkyl-N'-arylimidazolium salts via addition of imidazoles to arynes

[reaction: see text] A novel synthetic approach to N-alkyl-N'-arylimidazolium salts has been developed on the basis of addition of imidazoles to arynes. A variety of N-alkyl-N'-arylimidazolium salts can be synthesized straightforwardly in modest to good yields. Furthermore, utility of the resulting imidazolium salts has been demonstrated by the palladium-catalyzed Suzuki-Miyaura coupling of aryl chlorides.     

Facile synthesis of novel 3-substituted pyrido[1,2-a]pyrimidinium salts using vinamidinium salts

Pyrido[1,2-a]pyrimidinium salt derivatives 2a–f were prepared in good yields by condensation of 2-aminopyridine with 2-substituted vinamidinium salt derivatives 1a–f. The purity and the structure of the synthetized compounds were ascertained by elemental analysis, mass spectrometry, infrared, and NMR (¹H and ¹³C 400?MHz) spectroscopy.     

Solid-phase synthesis of biaryl cyclic peptides by borylation and microwave-assisted intramolecular Suzuki-Miyaura reaction

Miyaura borylation and Suzuki-Miyaura cross-coupling have been combined to set up an efficient strategy for the solid-phase synthesis of biaryl cyclic peptides. The Miyaura borylation was the key step in obtaining the linear peptidyl resin precursor containing both the boronate and the halogenated derivative of an aromatic amino acid. The Suzuki-Miyaura macrocyclization was performed under microwave irradiation leading to biaryl cyclic peptides of different ring sizes.     

Facile synthesis of 6-aryl 5-N-substituted pyridazinones: microwave-assisted Suzuki-Miyaura cross coupling of 6-chloropyridazinones

A facile synthesis of 5-dialkylamino-6-aryl-(2H)-pyridazin-3-one from 5,6-dichloropyridazinone was carried out by using a palladium-catalyzed Suzuki-Miyaura cross coupling of 6-chloro-5-dialkylaminopyridazinone 1 with various arylboronic acids (3 equiv) as the key transformation. The Suzuki-Miyaura cross-coupling reaction proceeded smoothly under microwave irradiation at 135-140 degrees C for 30 min with 5 mol % of Pd catalyst in moderate to good isolated yields. The use of a CombiPhos Pd6 mixture catalyst system and a single Pd-SPhos catalyst system was evaluated.     

Facile synthesis of highly congested 1,2-diphosphinobenzenes from bis(phosphine)boronium salts

[Structure: see text] Bis(phosphine)boronium salts 3a-c were designed and prepared as key building blocks for the synthesis of highly congested diphosphinobenzenes. The preparation of sterically hindered ortho-phenylene-bridged diphosphines 1a-c was achieved by the reaction of the bis(phosphine)boronium salts 3a-c with difluorobenzenechromium complex 2 and subsequent removal of the BH2 group. The steric nature of diphosphine 1a was revealed in single-crystal X-ray analysis of its Rh complex.     

Facile controlled synthesis and growth mechanisms of flower-like and tubular MnO2 nanostructures by microwave-assisted hydrothermal method

Birnessite flower-like and α-type tubular MnO(2) nanostructures were selectively synthesized through simple decomposition of KMnO(4) under hydrochloric acid condition by controlling reaction temperature using a microwave-assisted hydrothermal method. The as-prepared samples were characterized in detail by various techniques including X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, Fourier transform-infrared spectroscopy, and Raman scattering spectroscopy. While the growth of flower-like birnessite-MnO(2) might follow a widely accepted Ostwald ripening process, we proposed a formation mechanism of the nanotubular α-MnO(2) based on our evidence, which was assembly of nanorods through an "oriented attachment" process.     

Facile functionalization of gold nanoparticles via microwave-assisted 1,3 dipolar cycloaddition

This contribution describes a simple and facile method for the functionalization of thiol-coated gold nanoparticles using microwave-assisted 1,3 dipolar cycloadditions. The developed procedure allows for the attachment of terminal alkynes onto azide-containing gold nanoparticles in nearly quantitative conversions within minutes. The utility of the method has been demonstrated by attaching a library of substituted alkynes onto gold nanoparticles in nearly quantitative yields. In a proof of principle study, we demonstrate the potential use of this methodology in catalysis by attaching palladium catalysts to the azide-containing gold nanoparticles and investigate the resulting materials as supported catalysts in Suzuki couplings. Activities that rival the nonsupported analogues were observed, demonstrating that the nanoparticle support does not interfere with the catalytic activity.     

Stereoselective synthesis of novel C-azanucleoside analogues by microwave-assisted nucleophilic addition of sugar-derived cyclic nitrones

A series of C-azanucleoside analogues were synthesized by microwave-assisted nucleophilic addition of electron-rich hetero-aromatics to sugar-derived cyclic nitrones, and followed by reduction and deprotection. The nucleophilic addition afforded the 2′,3′-trans isomer as the dominant by the favorite exo attack and showed high stereoselectivity in polar solvent.