Highly efficient,general procedure for the preparation of alkylzinc reagents from unactivated alkyl bromides and chlorides

[reaction: see text] Alkylzinc bromides have been efficiently prepared by the direct insertion of zinc metal (dust, powder, granule, shot), activated with 1-5 mol % I(2), into alkyl bromides in a polar aprotic solvent. The zinc reagents thus formed undergo Ni- and Pd-catalyzed cross-coupling with aryl halides to produce functionalized alkylarenes in excellent yields.     

Kumada coupling of aryl, heteroaryl, and vinyl chlorides catalyzed by amido pincer nickel complexes

A series of amido pincer complexes of nickel were examined for their catalysis in the Kumada cross-coupling reaction. The P,N,O-pincer nickel complexes tested are active catalysts for the cross-coupling of aryl, heteroaryl, and vinyl chlorides with aryl Grignard reagents. The reactions can proceed at room temperature and tolerate functional groups in aryl chlorides with the aid of LiCl and ZnCl(2) additives.     

Stereoselective C(sp3)-C(sp2) Negishi coupling of (2-amido-1-phenylpropyl)zinc compounds through the steric control of β-amido group

A controllable diastereoselective C(sp2)-C(sp3) Negishi coupling reaction of secondary benzylic zinc reagents with aryl bromides has been demonstrated for the first time, forming medicinally important 1-arylphenylethylamines. In the presence of Pd(OAc) 2 and S-phos, open-chain (2-amido-1-phenylethyl)zinc reagents bearing a -NHAc or NHCHO group underwent cross-coupling reaction to give syn 1-arylphenylethylamine as the major products, whereas the zinc reagents bearing a sterically hindered-NHCOC(CH3)2 OTBS group specifically yielded anti 1-arylphenylethylamines.     

Transition metal catalyzed cross-coupling of aryl Grignard reagents with aryl fluorides via Pd- or Ni-activation of the C-F bond: an efficient synthesis of unsymmetrical biaryls - application of microwave technology in ligand and catalyst screening

Biaryl compounds are prevalent in both nature and in active pharmaceutical ingredients. The palladium and nickel catalyzed cross-coupling of aryl Grignard reagents with aryl fluorides reported herein affords moderate to excellent yields of the corresponding unsymmetrical biaryls. In addition, the first example of a biaryl cross-coupling utilizing unactivated aryl fluorides under phosphine free palladium conditions is reported. Microwave technology allowed rapid optimization of catalyst systems, which identified several ligands for this cross-coupling reaction.     

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.     

New efficient approach to 2,2-diaryl-1,1-difluoro-1-alkenes and 1,1-difluoro-2-aryl-1,3-dienes via Suzuki coupling of alpha-halo-beta,beta-difluorostyrenes

[reaction: see text] Alpha-halo-beta,beta-difluorostyrenes [ArCX = CF2; X = Br, I; Ar = aryl, heteroaryl; synthesized by the Pd(0)-catalyzed coupling reaction of the corresponding alpha-halo-beta,beta-difluoroethenylzinc reagents (CF2=CXZnCl, X = Br, I) with aryl iodides] were functionalized at the halogen site with arylboronic acids under Pd(0)-catalyzed Suzuki-Miyaura coupling reaction conditions to obtain 2,2-diaryl-1,1-difluoro-1-alkenes (ArAr'C=CF2, Ar' = aryl, heteroaryl) in 51-91% isolated yield. The corresponding reaction with alkenylboronic acids produced 1,1-difluoro-2-aryl-1,3-dienes in 53-80% isolated yield. Alternatively, 2,2-disubstituted-1,1-difluoro-1-alkenes were synthesized in moderate yield by a zinc-insertion reaction at the halogen site of the alpha-halo-beta,beta-difluorostyrenes, followed by Pd(0)-catalyzed cross-coupling of the zinc reagent with aryl or alkenyl iodides.     

Cross-coupling reactions of phenylmagnesium halides with fluoroazines and fluorodiazines

The first nickel-catalyzed cross-coupling reactions between fluoroarenes and aryl organometallics using commercially available ligands are described. The nickel-catalyzed cross-coupling reactions between aryl Grignard reagents and fluoroazines and -diazines occurred in THF at room temperature using commercially available 1,2-bis(diphenylphosphino)ethane, 1,3-bis(diphenylphosphino)propane, or 1,1'-bis(diphenylphosphino)ferrocene as ligand. Various fluoro substrates such as pyridines, diazines (pyrazine, pyridazine), benzodiazines (quinoxaline), and quinolines were successfully involved in the reaction with phenylmagnesium halides (phenylmagnesium chloride, 2-methoxyphenylmagnesium bromide, and 4-methoxyphenylmagnesium bromide). The conditions used also allowed the cross-coupling of 4-fluorotoluene with arylmagnesium reagents.     

Palladium-phosphinous acid-catalyzed cross-coupling of aryl and acyl halides with aryl-, alkyl-, and vinylzinc reagents

Several palladium-phosphinous acids have been prepared and employed in cross-coupling reactions of aryl or acyl halides with aliphatic and aromatic organozinc reagents. The POPd7-catalyzed reaction of aryl halides, including electron-rich aryl chlorides, and arylzinc reagents was found to afford biaryls exhibiting alkoxy, alkylthio, amino, ketone, cyano, nitro, ester, and heteroaryl groups in 75-93% yield. Excellent results were obtained with sterically hindered substrates which gave di- and tri -ortho-substituted biaryls in up to 92% yield. Aryl halides also undergo POPd7-catalyzed aryl-vinyl and aryl-alkyl bond formation under mild conditions. Styrenes and alkylarenes were prepared in 79-93% yield from aryl halides and vinyl or alkylzinc reagents. The replacement of aryl halides by acyl halides provides access to ketones which were produced in up to 98% yield when POPd was used as catalyst. This approach overcomes the limited substrate scope, reduced regiocontrol, and low functional group tolerance of traditional Friedel-Crafts acylation methods.     

Nickel-mediated decarbonylative cross-coupling of phthalimides with in situ generated diorganozinc reagents

The nickel-mediated cross-coupling of phthalimides with diorganozinc reagents proceeds via a decarbonylative process to produce ortho-substituted benzamides in high yields. In addition to tolerating diverse phthalimide functionality, including alkyl, aryl, and heteroatom containing substituents, this methodology proceeds smoothly with diorganozinc reagents prepared from aryl bromides and utilized without purification.     

Preparation of tertiary amides via aryl, heteroaryl, and benzyl organozinc reagents; scope and limitations

A facile synthetic protocol for the preparation of tertiary amides has been developed. The title compounds have been successfully obtained by the Pd-catalyzed cross-coupling reactions of readily available aryl and benzyl organozinc reagents with the appropriate carbamoyl chlorides.     

Cobalt-catalyzed preparation of arylindium reagents from aryl and heteroaryl bromides

A cobalt-bathophenanthroline catalyst has been developed for the direct preparation of a variety of arylindium reagents from the corresponding aryl and heteroaryl bromides in the presence of indium metal and lithium chloride. The thus-formed arylindium reagents undergo efficient palladium-catalyzed cross-coupling reactions with aryl iodides, tolerating various functional groups including hydroxy and free amino groups.     

Preparation and palladium-catalyzed cross-coupling of aryl triethylammonium bis(catechol) silicates with aryl triflates

Pentavalent aryl and heteroaryl bis(catechol) silicates undergo palladium-catalyzed cross-coupling with aryl and heteroaryl triflates in the presence of a fluoride source in excellent yields. These solid, air-stable bis(catechol) silicates are prepared from a high-yielding displacement reaction between catechol and an aryl siloxane in the presence of an amine base. The cross-coupling reaction is tolerant of a wide range of electron-donating and electron-withdrawing groups. Several examples of di-ortho-substituted triflates are successfully coupled with these reagents.     

Silver-catalyzed cross-coupling reactions of alkyl bromides with alkyl or aryl Grignard reagents

Treatment of secondary or tertiary alkyl bromides with alkyl Grignard reagents in the presence of catalytic amounts of silver bromide and potassium fluoride in CH₂Cl₂ afforded the corresponding cross-coupling products in reasonable yields. Moreover, silver showed catalytic activity for the cross-coupling reactions of alkyl bromides with aryl Grignard reagents.     

Oxidative cross-coupling through double transmetallation: surprisingly high selectivity for palladium-catalyzed cross-coupling of alkylzinc and alkynylstannanes

Two different organometallic reagents now can cross-couple together with the oxidative cross-coupling strategy. Palladium catalyzed oxidative cross-couplings of alkylzinc and alkynylstannane reagents using desyl chloride as the oxidant have been explored, which produce the desired Csp-Csp3 cross-coupling product in surprisingly high selectivity and yields. The current catalytic system tolerates the presence of beta-H, and the reactions using long chain alkyl zinc reagents gave the cross-coupling product in excellent yields and selectivities.     

Facile Access to Sterically Hindered Aryl Ketones via Carbonylative Cross-Coupling: Application to the Total Synthesis of Luteolin

A general and mild protocol for achieving the carbonylative cross-coupling of sterically hindered, ortho-disubstituted aryl ketones is reported. The commercially available PEPPSI-IPr catalyst is shown to efficiently promote the carbonylative cross-coupling of hindered ortho-disubstituted aryl iodides to give diaryl ketones; traditional phosphine catalysts are less effective. Carbonylative Suzuki-Miyaura cross-couplings provide a diverse array of biaryl ketones in good to excellent yields. The same catalyst is also shown to catalyze a carbonylative Negishi cross-coupling reaction, utilizing a variety of alkynyl-zinc reagents to give the corresponding alkynyl aryl ketones. Application of this new methodology to the synthesis of the natural product luteolin is reported.     

Efficient synthesis of sterically crowded biaryls by palladium-phosphinous acid-catalyzed cross-coupling of aryl halides and aryl grignards

A series of sterically hindered biaryls have been obtained by palladium- and nickel-phosphinous acid-catalyzed Kumada-Corriu cross-coupling of ortho-substituted aryl halides and Grignard reagents. This method allows formation of di- and tri-ortho-substituted biaryls in 87-98% yield under mild reaction conditions even when electron-rich aryl chlorides are used. The reaction also proceeds with aryl iodides at -20 degrees C, and under these conditions, functional groups that are generally not compatible with Grignard reagents are tolerated.     

Nickel-catalyzed cross-coupling reactions of benzylic zinc reagents with aromatic bromides, chlorides and tosylates

Benzylic zinc reagents prepared by direct insertion of zinc to benzylic chlorides in the presence of LiCl undergo smooth cross-coupling reactions with aromatic chlorides, bromides and tosylates using Ni(acac)(2) and PPh(3) as a catalyst system.     

Preparation of ethyl 2-aryl 2,3-alkadienoates via palladium-catalyzed selective cross-coupling reactions

Pd-catalyzed cross-coupling reactions of aryl iodides containing not only an electron-donating group but also an electron-withdrawing group on the aryl ring with organoindium reagents generated in situ from indium and ethyl 4-bromo-2-alkynoates produced selectively ethyl 2-aryl-2,3-alkadienoates in good yield.     

Iron-catalysed cross-coupling of halohydrins with aryl aluminium reagents: a protecting-group-free strategy attaining remarkable rate enhancement and diastereoinduction

Non-protected halohydrins are cross-coupled with aryl aluminium reagents to produce aryl alkanols in the presence of the iron-bisphosphine catalysts. Remarkable reaction rate enhancement and diastereoinduction are realized by the in situ generated aluminium alkoxides, offering a new method for the reactivity and selectivity control of the iron-catalysed cross-coupling reaction.     

Stereoselective Palladium-catalyzed Cross-coupling of (2-Amido-1-phenylpropyl)zinc Compounds with Aryl Bromides

A controllable diastereoselective C(sp²)―C(sp³) Negishi coupling reaction of secondary benzylic zinc reagents with aryl bromides to form medicinally important 2-arylphenylethylamines was demonstrated. In the presence of Pd(OAc)₂ and 2-dicyclohexylphosphino-2',6'-dimethoxybiphenyl(S-phos), open-chain(2-amido-1-phenylethyl)zinc reagent bearing a β-NHAc or NHCHO group undergoes coupling reaction to give syn-1-arylphenylethylamine mainly, whereas the zinc reagent bearing a sterically hindered β-amido group, for example NHCOC(CH₃)₂OTBS undergoes the coupling reaction to yield anti-1-arylphenylethylamines with a configuration inversion. In addition, a working mechanism for the stereoselective Negishi cross-coupling was also proposed.