Heteroaryl manganese reagents: direct preparation and reactivity studies

Direct preparation of various heteroaryl manganese reagents was performed by using highly active manganese (Mn∗) and heteroaryl halides. The resulting organomanganese reagents were coupled with electrophiles such as aryl halides, vinyl halides, and benzoyl chlorides under mild reaction conditions. The corresponding coupling products were obtained in good yields.     

Efficient Negishi coupling reactions of aryl chlorides catalyzed by binuclear and mononuclear nickel-N-heterocyclic carbene complexes

We describe the first nickel-N-heterocyclic carbene catalyzed Negishi cross-coupling reaction of a variety of unactivated aryl chlorides, heterocyclic chlorides, aryl dichlorides, and vinyl chloride. The mononuclear and binuclear nickel-NHC complexes supported by heteroarene-functionalized NHC ligands are found to be highly efficient for the coupling of unactivated aryl chlorides and organozinc reagents, leading to biaryls and terphenyls in good to excellent yields under mild conditions. For all aryl chlorides, the binuclear nickel catalysts show activities higher than those of mononuclear nickel complexes because of possible bimetallic cooperative effect.     

A new approach to organomanganese compounds: the tellurium/manganese exchange reaction

Diorganomanganese compounds react with aryl, vinyl, and alkynyl tellurides in a tellurium/manganese exchange reaction. The new mixed organomanganese reagents react selectively with electrophiles.     

Cobalt-Xantphos-catalyzed, LiCl-mediated preparation of arylzinc reagents from aryl iodides, bromides, and chlorides

A cobalt-Xantphos-catalyzed, LiCl-mediated system has been developed for the direct and expedient preparation of arylzinc reagents in THF from the corresponding aryl iodides, bromides, and chlorides. Owing to the use of THF as a versatile solvent, the thus-formed arylzinc reagents displayed a high degree of compatibility with a variety of conventional as well as newly emerging metal-catalyzed cross-coupling reactions.     

Manganese-catalyzed oxidative homo-coupling of aryl Grignard chlorides

Manganese-catalyzed homo-coupling of aryl magnesium chlorides to give biphenyls was successfully achieved using manganese chloride as catalyst. A variety of aryl magnesium chlorides were efficiently converted into the corresponding symmetrical biaryls using 10 mol% MnCl₂ as catalyst in the presence of a stoichiometric amount of 1,2-dichloroethane. Since the aryl chlorides, from which the Grignard reagents were prepared, are cheaper and more readily available that the corresponding bromides and iodides this procedure should become the method of choice for preparing symmetrical biaryls.     

Preparation of functionalized organomanganese(II) reagents by direct insertion of manganese to aromatic and benzylic halides

Functionalized arylmanganese compounds were prepared using commercial manganese powder in the presence of LiCl and catalytic amounts of both 2.5% InCl(3) and 2.5% PbCl(2) (THF, 0-50 °C). In addition, benzylic manganese reagents are obtained at 25 °C in ca. 70-80% yield (in the absence of LiCl) using commercial manganese powder and catalytic amounts of 2.5% InCl(3) and 2.5% PbCl(2). The resulting organomanganese reagents undergo smooth 1,2-addition, acylation, allylic substitution, Pd-catalyzed cross-coupling, and copper-catalyzed conjugate addition, affording the desired products in good yields.     

Copper-catalyzed conversion of aryl and heteroaryl bromides into the corresponding chlorides

An efficient method for the synthesis of aryl and heteroaryl chlorides is described. The reactions of aryl and heteroaryl bromides with tetramethylammonium chloride proceeded smoothly in the presence of a copper catalyst under mild reaction conditions to produce the corresponding chlorides in satisfactory to excellent yields.     

One-pot Negishi cross-coupling reactions of in situ generated zinc reagents with aryl chlorides, bromides, and triflates

In situ generated aryl, heteroaryl, alkyl, or benzylic polyfunctional zinc reagents obtained by the addition of zinc and LiCl to the corresponding organic iodides undergo smooth Pd(0)-catalyzed cross-coupling reactions with aryl bromides, chlorides, and triflates in the presence of PEPPSI as a catalyst. This procedure avoids the manipulation of water and air-sensitive organozinc reagents and produces cross-coupling products in high yields.     

Rapid and efficient Pd-catalyzed Sonogashira coupling of aryl chlorides

An efficient and effective microwave-assisted cross-coupling of terminal alkynes with various aryl chlorides including sterically hindered, electron-rich, electron-neutral, and electron-deficient aryl chloride is developed. It proceeds faster and generally gives good to excellent yields and also can be extended successfully to the Suzuki coupling and Buchwald-Hartwig amination, as well as the Heck coupling with inert aryl chlorides. The short reaction times and simple reaction conditions coupling with a broad substrate scope render this method particularly attractive for the efficient preparation of biologically and medicinally interesting molecules.     

A selective synthesis of alkenylmercuric chlorides via alkenylalanes

The reaction of alkenylalanes with mercuric chloride in THF produces stereospecically the coresponding alkenylmercuric chlorides in high yields.     

Versatile palladium(II)-catalyzed Negishi coupling reactions with functionalized conjugated alkenyl chlorides

Under palladium catalysis, we found that organozincate reagents, generated in situ, by reaction of Grignard compounds with less than molar amounts of zinc chloride, in the presence of conjugated alkenyl chlorides, give rapidly and cleanly the corresponding coupling product in high yields. In this way, aryl as well as primary and secondary alkyl substituents have been introduced successfully. The selectivity of the reaction allows to prepare various functionalized conjugated enynes and dienes from chloroenyne and chlorodiene derivatives bearing a functional group.     

A mild Negishi cross-coupling of 2-heterocyclic organozinc reagents and aryl chlorides

A mild Negishi cross-coupling of 2-heterocyclic organozinc reagents and aryl chlorides is described. The use of Pd(2)(dba)(3) and X-Phos as a ligand provides high yields for many examples. An efficient method to generate the organozinc reagents at room temperature is also demonstrated.     

An efficient system for the Pd-catalyzed cross-coupling of amides and aryl chlorides

A catalyst based on a new biarylphosphine ligand (3) for the Pd-catalyzed cross-coupling reactions of amides and aryl chlorides is described. This system shows the highest turnover frequencies reported to date for these reactions, especially for aryl chloride substrates bearing an ortho substituent. An array of amides and aryl chlorides were successfully reacted in good to excellent yields.     

Organomanganese (II) reagents XVIII: Copper-catalyzed 1,4- addition of organomanganese chloride compounds to conjugated ethylenic aldehydes

Organomanganese chlorides react with β-mono or β,β-bisubstituted ,β-ethylenic aldehydes in the presence of a catalytic amount of copper chloride to give good yields of 1,4-addition products in THF at −30°C.     

An easy coupling of acid chlorides into α-diketones promoted by diiodosamarium

In THF solution at room temperature, a very fast reaction occurs between acid chlorides RCOCl and two equivalents of diiodosamarium. The α-diketone RCOCOR are obtained in yields from 40 % (R = alkyl) to 80% (R = aryl).     

Preparation of aryl ketones via Ni-catalyzed Negishi-coupling reactions with acid chlorides

A Ni-catalyst-catalyzed cross-coupling reaction of organozinc reagents with acid chlorides has been successfully developed. Mild reaction conditions were required to complete the coupling reactions affording the corresponding aryl ketones in good to excellent yields.     

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.     

Microwave-promoted cross-coupling of acid chlorides with arylboronic acids: a convenient method for preparing aromatic ketones

Simple catalytic systems for cross-coupling reactions of acyl chlorides with arylboronic acids under microwave conditions were tested. Microwave irradiation facilitated the reaction course. Mild reaction conditions afford the symmetrical and unsymmetrical aryl ketones in reasonable to high yields within a short time. A wide range of substrates bearing an electron-donating or an electron-withdrawing substituent on aryl ring of acid chloride as well as on boronic acid were examined and high yields of ketones were produced.     

Preparation of Solid,Substituted Allylic Zinc Reagents and Their Reactions with Electrophiles

The treatment of various allylic chlorides or bromides with zinc dust in the presence of lithium chloride and magnesium pivalate (Mg(OCOtBu)₂) in THF affords allylic zinc reagents which, after evaporation of the solvent, produce solid zinc reagents that display excellent thermal stability. These allylic reagents undergo Pd‐catalyzed cross‐coupling reactions with PEPPSI‐IPent, as well as highly regioselective and diastereoselective additions to aryl ketones and aldehydes. Acylation with various acid chlorides regioselectively produces the corresponding homoallylic ketones, with the new C? C bond always being formed on the most hindered carbon of the allylic system.     

Homogeneous palladium-catalysed arylation of activated alkenes with aryl chlorides

A study has been made of arylation of activated alkenes with aryl chlorides homogeneously catalysed by palladium acetate in the presence of triphenylphosphine or tri-p-tolylphosphine. Electron-withdrawing substituents in the aryl chloride favour the reaction. Only moderate yields could be obtained, and the maximum turnover number was 51, mainly because of precipitation of palladium metal. The probable mechanism of the reaction is discussed.