One-pot copper-catalyzed synthesis of N-functionalized pyrazoles from boronic acids

A straight-forward route to prepare a diverse set of N-aryl pyrazoles via a one-pot copper-catalyzed boronic acid coupling and cyclization protocol is presented. A variety of aryl and heteroaryl N-functionalized pyrazoles not easily accessible by other means were formed in good yield from readily available boronic acid precursors in an operationally simple procedure.     

A mild and efficient copper-catalyzed N-arylation of unprotected sulfonimidamides using boronic acids

An efficient and low cost copper catalyzed system for N-arylation of sulfonimidamides has been developed. The reaction proceeds at room temperature under base free conditions. Various N-aryl, N-heteroaryl, and N-cyclopropyl sulfonimidamides were obtained in good to excellent yields.     

Pd-catalyzed direct arylation of tautomerizable heterocycles with aryl boronic acids via C-OH bond activation using phosphonium salts

The first direct arylation via C-OH bond activation of tautomerizable heterocycles has been achieved using phosphonium salts, on the basis of a combination of the phosphonium coupling and Suzuki-Miyaura cross-coupling conditions. Optimal reaction condition is obtained through screening of phosphonium salts, Pd catalysts, and bases. The direct arylation via C-OH bond activation tolerates a variety of tautomerizable heterocycles and aryl boronic acids. The mechanism of the Pd-catalyzed phosphonium coupling is proposed to proceed via a domino seven-step process including the unprecedented heterocycle-Pd(II)-phosphonium species. Application of the Pd-catalyzed direct arylation via C-OH bond activation using PyBroP leads to the most efficient synthesis of the biologically important 6-arylpurine ribonucleoside in a single step from unactivated and unprotected inosine.     

A copper-catalyzed domino radical cyclization route to benzospiro-indolizidinepyrrolidinones

In this Letter the synthesis of benzospiro-indolizidinepyrrolidinones is described by a domino atom transfer radical cyclization reaction using a copper catalyst. The structure of one of the products was established by single crystal X-ray diffraction. The investigated precursors, bearing a homo allyl substituent on the N-indole, result in a 5-exo-trig, followed by a 6-endo-trig cyclization. When the N-indole is substituted with an allyl group, only the spiro-cyclization occurs.     

N-substituted imines by the copper-catalyzed N-imination of boronic acids and organostannanes with O-acyl ketoximes

Catalytic quantities of copper(I) or copper(II) sources catalyze the N-imination of boronic acids and organostannanes through reaction with oxime O-carboxylates under nonbasic conditions. This method tolerates various functional groups and takes place efficiently using aryl, heteroaryl, and alkenyl boronic acids and stannanes.     

A direct route to triazole boronic esters and their application in the synthesis of small molecule arrays

Alkynylboronates represent useful substrates for the direct synthesis of triazole boronic esters by their thermal cycloaddition with azides. A telescoped cycloaddition-cross-coupling protocol is reported and its employment in the synthesis of a small triazole array is disclosed.     

CuI-catalyzed direct synthesis of diaryl thioethers from aryl boronic acids and arylsulfonyl chlorides

A CuI-catalyzed direct coupling of aryl boronic acids with arylsulfonyl chlorides for the preparation of diaryl thioethers was developed. The reaction is initiated by a PPh₃ reduction of the arylsulfonyl chloride, followed by a CuI-catalyzed C–S coupling with an aryl boronic acid. Various arylsulfonyl chlorides can directly serve as a sulfur source in this mild and efficient reaction giving the desired products in moderate to good yields. Moreover, this practical method has also been applied to the thioetherification of aryl iodides and acetylacetones.     

Palladium-catalyzed, direct boronic acid synthesis from aryl chlorides: a simplified route to diverse boronate ester derivatives

Although much current research focuses on developing new boron reagents and identifying robust catalytic systems for the cross-coupling of these reagents, the fundamental preparations of the nucleophilic partners (i.e., boronic acids and derivatives) has been studied to a lesser extent. Most current methods to access boronic acids are indirect and require harsh conditions or expensive reagents. A simple and efficient palladium-catalyzed, direct synthesis of arylboronic acids from the corresponding aryl chlorides using an underutilized reagent, tetrahydroxydiboron B(2)(OH)(4), is reported. To ensure preservation of the carbon-boron bond, the boronic acids were efficiently converted to the trifluoroborate derivatives in good to excellent yields without the use of a workup or isolation. Further, the intermediate boronic acids can be easily converted to a wide range of useful boronates. Finally, a two-step, one-pot method was developed to couple two aryl chlorides efficiently in a Suzuki-Miyaura-type reaction.     

A 2-pyrone cycloaddition route to functionalised aromatic boronic esters

A [4+2] cycloaddition/retro-cycloaddition route to functionalised aromatic boronic esters is outlined. A range of electron deficient dienes (2-pyrones) and dienophiles (alkynylboronates) were found to participate in the reaction. Furthermore, high levels of regiocontrol could be obtained in this process and a consistent mode of alkyne insertion has been uncovered.     

An enantioselective route to paeonilactone A via palladium- and copper-catalyzed reactions

We herein report on a formal total synthesis of paeonilactone A involving palladium-, copper-, and enzyme-catalyzed reactions starting from 1,3-cyclohexadiene. The key step in the synthesis, a palladium(II)-catalyzed 1,4-oxylactonization of a conjugated diene, simultaneously introduces two of the oxygen substituents required for the target molecule. The synthesis also includes our recently developed copper(I)-catalyzed cross-coupling reaction between dienyltriflates with Grignard reagents, introducing one of the methyl groups present in the target molecule. This new approach toward paeonilactone A allows complete control of all four stereogenic centers and is the first enantioselective route toward paeonilactone A starting from an achiral substrate.     

A directed chiral synthesis of amino acids from boronic esters

Conversion of (s)-pinanediol (1S)-1-haloalkylboronates to (1R)-1-azido boronates, homologation with (dichloromethyl)lithium to 1-chloro-2-azido boronates, oxidation with sodium chlorite to the α-azido acids, and catalytic hydrogenation yielded L-amino acids, 92-96% enantiomeric excess.     

A direct electrochemical route from ilmenite to hydrogen-storage ferrotitanium alloys

An unrecognised but predictable need for a hydrogen-supported society is tens or even hundreds of million tonnes of hydrogen-storage materials, and thus challenges existing technologies in terms of resource and economical realities. Ilmenite is an abundant mineral, and ferrotitanium alloys are among the earliest known hydrogen-storage materials. At present, industrial production of ferrotitanium alloys goes through separate extraction of individual metals, followed by a multistep arc-melting process. In particular, the extraction of titanium from ilmenite is highly energy intensive and tedious, accounting for titanium's high market price and restricted uses. This article reports the electrochemical synthesis of various ferrotitanium alloy powders directly from solid ilmenite in molten calcium chloride. More importantly, it demonstrates, for the first time, that such produced alloy powders can be used without further treatment for hydrogen storage and perform comparably with or better than similar products by means of other methods, but cost just a fraction.     

Merging visible-light photocatalysis and transition-metal catalysis in the copper-catalyzed trifluoromethylation of boronic acids with CF3I

This communication describes the development of a mild method for the cross-coupling of arylboronic acids with CF(3)I via the merger of photoredox and Cu catalysis. This method has been applied to the trifluoromethylation of electronically diverse aromatic and heteroaromatic substrates and tolerates many common functional groups.     

A general copper-catalyzed sulfonylation of arylboronic acids

A general copper-catalyzed method for the sulfonylation of arylboronic acids with sulfinate salts is described. A variety of alkyl-aryl, diaryl, and alkyl-heteroaryl sulfones were synthesized in good yield.     

Molecular tectonics. Use of the hydrogen bonding of boronic acids to direct supramolecular construction

Tetraboronic acids 1 and 2 have four -B(OH)(2) groups oriented tetrahedrally by cores derived from tetraphenylmethane and tetraphenylsilane. Crystallization produces isostructural diamondoid networks held together by hydrogen bonding of the -B(OH)(2) groups, in accord with the tendency of simple arylboronic acids to form cyclic hydrogen-bonded dimers in the solid state. Five-fold interpenetration of the networks is observed, but 60% and 64% of the volumes of crystals of tetraboronic acids 1 and 2, respectively, remain available for the inclusion of disordered guests. Guests occupy two types of interconnected channels aligned with the a and b axes; those in crystals of tetraphenylmethane 1 measure approximately 5.9 x 5.9 A(2) and 5.2 x 8.6 A(2) in cross section at the narrowest points, whereas those in crystals of tetraphenylsilane 2 are approximately 6.4 x 6.4 A(2) and 6.4 x 9.0 A(2). These channels provide access to the interior and permit guests to be exchanged quantitatively without loss of crystallinity. Because the Si-C bonds at the core of tetraboronic acid 2 are longer (1.889(3) A) than the C-C bonds at the core of tetraboronic acid 1 (1.519(6) A), the resulting network is expanded rationally. By associating to form robust isostructural networks with predictable architectures and properties of porosity, compounds 1 and 2 underscore the usefulness of molecular tectonics as a strategy for making ordered materials.     

The intramolecular sila-Pummerer cyclization: A new route to sulfur heterocycles

The generality of the intramolecular cyclization of suitable nucleophilic sites to a  S⁺CH₂ center created by a sila-Pummerer rearrangement has been investigated. Successful nucleophilic sites included the OH group (in alcohols, carboxylic acids, and hydroxylamines) and the NH group (in amines and carbamates): attempts to produce carbon-based nucleophilic sites were not effective. Successful cyclizations were achieved to produce sulfur heterocycles with 5-, 6-, and 7-membered rings.     

A synthetic route to enediyne-bridged amino acids

A general strategy for the preparation of enediyne-bridged amino acids has been disclosed. A cross-coupling reaction between amino- and carboxyl-modified amino acids under Sonogashira reaction conditions gave a protected enediyne-peptide conjugate. The model obtained can be used as a template in studies of Bergman cycloaromatization or peptide conformational preferences induced by the presence of the enediyne moiety.