A recyclable and base-free method for the synthesis of 3-iodothiophenes by the iodoheterocyclisation of 1-mercapto-3-alkyn-2-ols in ionic liquids.

The first example of an iodocyclisation reaction made recyclable by the use of an ionic liquid as the reaction medium is reported. Readily available 1-mercapto-3-alkyn-2-ols were smoothly converted into the corresponding 3-iodothiophenes (50-81% yields, 10 examples) when allowed to react with iodine (1-2 equiv.) in a proper ionic liquid, such as 1-ethyl-3-methylimidazolium ethyl sulfate (EmimEtSO4), as the solvent under mild reaction conditions (25 °C) and in the absence of an external base. The reaction medium can be recycled several times without significantly affecting the reaction outcome. Theoretical calculations have also been performed to investigate the role of the ionic liquid anion in the reaction.

Use of benzynes for the synthesis of heterocycles.

About two decades after Kobayashi's discovery in 1983 of a very mild way of generating highly reactive aryne intermediates, the synthetic community embraced o-(trimethylsilyl)aryl triflates as convenient and versatile aryne precursors for the synthesis of carbocycles and heterocycles, as well as natural products and pharmaceutically promising drug candidates. This review provides a comprehensive overview of the construction of heterocycles using Kobayashi's silylaryl triflate aryne precursors. It is organized according to the type of heterocycle generated.

Intermolecular C-O Addition of Carboxylic Acids to Arynes: Synthesis of o-Hydroxyaryl Ketones, Xanthones, 4-Chromanones, and Flavones.

An efficient and simple route to biologically and pharmaceutically important o-hydroxyaryl ketones, xanthones, 4-chromanones, and flavones has been developed utilizing readily available carboxylic acids and commercially available o-(trimethylsilyl)aryl triflates.

Efficient Microwave-assisted One-pot Three-component Synthesis of 2,3-Disubstituted Benzofurans under Sonogashira Conditions.

An efficient one-pot method for the synthesis of 2,3-disubstituted benzo[b]furans from commercially available 2-iodophenols, terminal acetylenes and aryl iodides has been developed utilizing Sonogashira reaction conditions. After an initial Sonogashira coupling of the 2-iodophenol with the terminal alkyne, cyclization involving the aryl iodide provides the 2,3-disubstituted benzo[b]furan in good to excellent yields. The use of microwave irradiation shortens the reaction times and minimizes the side products. This methodology is especially useful for the construction of libraries of highly substituted benzo[b]furans and their analogues.

Synthesis of o-(dimethylamino)aryl ketones, acridones, acridinium salts, and 1H-indazoles by the reaction of hydrazones and arynes.

A novel, efficient route to biologically and pharmaceutically important o-(dimethylamino)aryl ketones, acridones, acridinium salts, and 1H-indazoles has been developed starting from readily available hydrazones of aldehydes and o-(trimethylsilyl)aryl triflates. The reaction proceeds through arynes under mild conditions, tolerates a wide range of functional groups, and provides the final products in good to excellent yields.

Synthesis of N-acylcarbazoles through palladium-catalyzed aryne annulation of 2-haloacetanilides.

N-Acylcarbazoles have been synthesized in moderate to good yields by the annulation of in situ generated arynes with 2-haloacetanilides in the presence of a palladium catalyst and CsF. Both C-C and C-N bonds are formed simultaneously, and a variety of functional groups are tolerated in this reaction.

Regio- and stereoselective synthesis of cyclic imidates via electrophilic cyclization of 2-(1-alkynyl)benzamides. A correction.

The electrophilic cyclization of 2-(1-alkynyl)benzamides affords high yields of cyclic imidates, instead of the previously reported isoindolin-1-ones, where cyclization proceeds on the oxygen of the carbonyl group rather than the nitrogen of the amide functionality. X-ray crystallography and spectroscopic techniques have been used to characterize the products. A correction is hereby provided in order to rectify the previous misassignment of structure.

Palladium-catalyzed annulation of arynes by o-halobenzamides: synthesis of phenanthridinones.

The palladium-catalyzed annulation of arynes by substituted o-halobenzamides produces N-substituted phenanthridinones in good yields. This methodology provides this important heterocyclic ring system in a single step by simultaneous C-C and C-N bond formation, under relatively mild reaction conditions, and tolerates a variety of functional groups.

Synthesis of benzisoxazolines by the coupling of arynes with nitrones.

A variety of substituted benzisoxazolines have been synthesized by the [3 + 2] cycloaddition of nitrones and arynes. The reaction scope is broad, the reaction conditions are mild, and the process tolerates a variety of functional groups.

An iodocyclization approach to substituted 3-iodothiophenes.

A novel approach to 3-iodothiophenes by direct iodocyclization of alkynylthiol derivatives is presented. A variety of 1-mercapto-3-yn-2-ols 5 (readily available from alkynylation of the corresponding alpha-mercapto ketones or alpha-mercapto esters) were smoothly converted into the corresponding 3-iodothiophene derivatives 6 in good yields by reaction with molecular iodine in the presence of NaHCO(3) at room temperature in MeCN as the solvent.

Formation of acridones by ethylene extrusion in the reaction of arynes with ß-lactams and dihydroquinolinones.

N-Unsubstituted ß-lactams react with a molecule of aryne by insertion into the amide bond to form a 2,3-dihydroquinolin-4-one, which subsequently reacts with another molecule of aryne to form an acridone by extrusion of a molecule of ethylene. 2,3-Dihydroquinolin-4-ones react under the same reaction conditions to afford identical results. This is the first example of ethylene extrusion in aryne chemistry.

Synthesis of pyrido[1,2-a]indole malonates and amines through aryne annulation.

Pyrido[1,2-a]indoles are known as medicinally and pharmaceutically important compounds, but there is a lack of efficient methods for their synthesis. We report a convenient and efficient route to these privileged structures starting from easily accessible 2-substituted pyridines and aryne precursors. A small library of compounds has been synthesized utilizing the developed method, affording variously substituted pyrido[1,2-a]indoles in moderate to good yields.

One-pot synthesis of 1-alkyl-1H-indazoles from 1,1-dialkylhydrazones via aryne annulation.

The reaction of readily accessible 1,1-dialkylhydrazones with commercially available o-(trimethylsilyl)aryl triflates provides a direct one-step route to pharmaceutically important 1-alkylindazoles. The products are obtained in high yields by one-pot NCS-chlorination/aryne annulation or Ac(2)O-acylation/deprotection/aromatization protocols.

Aryne [3 + 2] cycloaddition with N-sulfonylpyridinium imides and in situ generated N-sulfonylisoquinolinium imides: a potential route to pyrido[1,2-b]indazoles and indazolo[3,2-a]isoquinolines.

The aryne [3 + 2] cycloaddition process with pyridinium imides breaks the aromaticity of the pyridine ring. By equipping the imide nitrogen with a sulfonyl group, the intermediate readily eliminates a sulfinate anion to restore the aromaticity, leading to the formation of pyrido[1,2-b]indazoles. The scope and limitation of this reaction are discussed. As an extension of this chemistry, N-tosylisoquinolinium imides, generated in situ from N'-(2-alkynylbenzylidene)-tosylhydrazides via an AgOTf-catalyzed 6-endo-dig electrophilic cyclization, readily undergo aryne [3 + 2] cycloaddition to afford indazolo[3,2-a]-isoquinolines in the same pot, offering a highly efficient route to these potential anticancer agents.

Nucleophilic addition to 2,3-pyridyne and synthesis of benzonaphthyridinones.

A study of the nucleophilic addition of amines to 2,3-pyridyne has been carried out. 2-Aminopyridines have been generated exclusively. A series of benzonaphthyridinones have been synthesized by reacting 2,3-pyridyne and o-aminobenzoates.

Synthesis of 9-Substituted Xanthenes by the Condensation of Arynes with ortho-Hydroxychalcones.

The reaction of o-(trimethylsilyl)aryl triflates, CsF, and o-hydroxychalcones affords a general and efficient way to prepare biologically interesting 9-substituted xanthenes. This chemistry presumably proceeds by tandem intermolecular nucleophilic attack of the phenoxide of the chalcone on the aryne and subsequent intramolecular Michael addition. The introduction of an external base, Cs(2)CO(3), has proven beneficial in this reaction.

Synthesis of N-arylisatins by the reaction of arynes with methyl 2-oxo-2-(arylamino)acetates.

N-Arylisatins are efficiently prepared by the reaction of 2-oxo-2-(arylamino)acetates and arynes under mild reaction conditions.

Synthesis of 2H-indazoles by the [3 + 2] dipolar cycloaddition of sydnones with arynes.

A rapid and efficient synthesis of 2H-indazoles has been developed using a [3 + 2] dipolar cycloaddition of sydnones and arynes. A series of 2H-indazoles have been prepared in good to excellent yields using this protocol, and subsequent Pd-catalyzed coupling reactions can be applied to the halogenated products to generate a structurally diverse library of indazoles.

Synthesis of pyrido[1,2-b]indazoles via aryne [3 + 2] cycloaddition with N-tosylpyridinium imides.

The [3 + 2] cycloaddition of arynes with N-tosylpyridinium imides, followed by an elimination of Ts(-), affords pyrido[1,2-b]indazoles under mild reaction conditions in good yields.

Preparation and properties of aqueous castor oil-based polyurethane-silica nanocomposite dispersions through a sol-gel process.

Waterborne castor oil-based polyurethane-silica nanocomposites with the polymer matrix and silica nanoparticles chemically bonded have been successfully prepared through a sol-gel process. The formation of silica nanoparticles in water not only reinforces the resulting coatings, but also increases the crosslink density of the nanocomposites. The (29)Si solid state NMR spectrum indicates the formation of silica and the TEM indicates that the nanoparticles are embedded in the polymers, resembling a core-shell structure. The silica nanoparticles in the polymer matrix play an important role in improving both the mechanical properties and the thermal stabilities of the resulting nanocomposites. This work provides an effective and promising way to prepare biorenewable, high performance nanocomposite coatings.