- Diboron-Promoted Reduction of Ni(II) Salts: Precatalyst Activation Studies Relevant to Ni-Catalyzed Borylation Reactions
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The activation and reduction of nickel(II) salts under conditions relevant to Ni-catalyzed borylation reactions is reported. Methanolic solutions of NiCl2·6H2O reacted with >2 equiv of (iPr)2NEt were converted to polymeric Ni(OMe)2, which was characterized by IR spectroscopy, magnetic susceptibility measurements, and verified by independent synthesis from NaOMe. When diboron reagents such as bis(neopentylglycolato) diboron (B2(npg)2) were exposed to methanolic solutions of Ni(II) salts and (iPr)2NEt, nickel metal was deposited along with the evolution of hydrogen gas. A direct relationship between yield of nickel metal and equivalents of B2(npg)2 relative to [Ni] was also observed, reaching >99% yield at 8 equiv. Ni(0) coordination complexes were also isolated when a phosphine, phosphite, and/or diene ligand was present, all starting from NiCl2·6H2O, including the following: Ni[P(OPh)3]4 (74% yield), Ni[P(OiPr)3]4 (54% yield), Ni(PPh3)4 (75% yield), (dppp)2Ni + Ni(1,5-cod)2 (dppp = 1,3-bis(diphenylphosphine)propane) (91% yield), Ni(1,5-cod)2 (1,5-cod = 1,5-cyclooctadiene) (69% yield), and (dppf)Ni(1,5-cod) (dppf = 1,1′-bis(diphenylphosphino)ferrocene) (84% yield). The high yields observed indicated the efficient reduction of Ni(II) to Ni(0) and a likely route for precatalyst entry into the Ni-borylation catalytic cycle. These in situ reduction conditions were also successfully applied to a previously developed Ni-catalyzed alpha-arylation reaction where the requisite Ni(1,5-cod)2 precatalyst was substituted for NiCl2·6H2O and catalytic diboron. Comparable yields to the original report were observed under these conditions, further demonstrating that Ni(0) active species can be efficiently accessed with diboron reagents under protic conditions from Ni(II) salt hydrates.
- Joannou, Matthew V.,Sarjeant, Amy A.,Wisniewski, Steven R.
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p. 2691 - 2700
(2021/08/20)
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- Enantioselective Intramolecular Hydroacylation of Unactivated Alkenes: An NHC-Catalyzed Robust and Versatile Formation of Cyclic Chiral Ketones
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A highly enantioselective intramolecular N-heterocyclic carbene (NHC)-catalyzed hydroacylation reaction gives access to a range of cyclic ketones from unactivated olefin-substituted aldehydes (up to 99% ee). Remarkably, aliphatic aldehydes were also transformed efficiently in an NHC-catalyzed hydroacylation reaction for the first time. 100% Organic: A highly enantioselective N-heterocyclic carbene (NHC)-catalyzed intramolecular hydroacylation of aromatic and, more interestingly, aliphatic aldehydes with unactivated olefins offers access to a range of cyclic α-chiral ketones bearing quaternary centers. The reaction was found to be highly robust and proceeds with excellent yield in the presence of a diverse range of functional groups.
- Janssen-Müller, Daniel,Schedler, Michael,Fleige, Mirco,Daniliuc, Constantin G.,Glorius, Frank
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p. 12492 - 12496
(2015/10/12)
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- Nickel-catalyzed enantioselective C-C bond formation through C sp 2 -O cleavage in aryl esters
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We report the first enantioselective C-C bond formation through C-O bond cleavage using aryl ester counterparts. This method is characterized by its wide substrate scope and results in the formation of quaternary stereogenic centers with high yields and asymmetric induction.
- Cornella, Josep,Jackson, Evan P.,Martin, Ruben
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supporting information
p. 4075 - 4078
(2015/03/30)
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- Enantioselective α-arylation of cyclic ketones catalyzed by a combination of an unmodified Cinchona alkaloid and a palladium complex
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A palladium/Cinchona alkaloid-catalyzed α-arylation between cyclic ketones and aryl halides under phosphine-free conditions is presented. The use of a simple, unmodified Cinchona alkaloid results in high levels of activity and selectivity with up to 93% ee. These enantioinduction levels are comparable or even higher than the ones reported using palladium/BINAP complexes. To the best of our knowledge, this represents the first use of unmodified Cinchona alkaloids as ligands/catalysts in asymmetric transition metal complex-catalyzed cross-coupling reactions. Copyright
- Richter, Christian,Ranganath, Kalluri V. S.,Glorius, Frank
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supporting information; experimental part
p. 377 - 382
(2012/04/11)
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- Nickel-catalyzed asymmetric α-arylation and heteroarylation of ketones with chloroarenes: Effect of halide on selectivity, oxidation state, and room-temperature reactions
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We report the α-arylation of ketones with a range of aryl chlorides with enantioselectivities from 90 to 99% ee catalyzed by the combination of Ni(COD)2 and (R)-BINAP and the coupling of ketones with a range of heteroaryl chlorides with enantioselectivities up to 99% ee catalyzed by Ni(COD)2 and (R)-DIFLUORPHOS. The analogous reactions of bromoarenes occur with much lower enantioselectivities. Mechanistic studies showed that the difference in the rates of decomposition of the arylnickel(II) halide intermediates to {[(R)-BINAP]NiX}2 likely accounts for the difference in the enantioselectivities of the reactions of bromoarenes and chloroarenes. This catalyst decomposition can be overcome by conducting the reactions with [(R)-BINAP]Ni(η2-NC-Ph) (4), which undergoes oxidative addition to haloarenes at room temperature.
- Ge, Shaozhong,Hartwig, John F.
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supporting information; experimental part
p. 16330 - 16333
(2011/11/29)
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- Enantioselective α-arylation of ketones with aryl triflates catalyzed by difluorphos complexes of palladium and nickel
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The asymmetric α-arylation of ketones with aryl triflates is described, and the use of this electrophile with nickel and palladium catalysts containing a segphos derivative increases substantially the scope of highly enantioselective arylations of ketone enolates. The combination of aryl triflates as reactant, difluorphos as ligand, palladium catalysts for reactions of electron-neutral or electron-rich aryl triflates, and nickel catalysts for reactions of electron-poor aryl triflates led to a series of α-arylations of tetralone, indanone, cyclopentanone, and cyclohexanone derivatives. Enantioselectivities ranged from 70% to 98% with 10 examples over 90%. Systematic studies on these α-arylations have revealed a number of factors that affect enantioselectivity. Ligands containing biaryl backbones with smaller dihedral angles generate catalysts that react with higher enantioselectivity than related ligands with larger dihedral angles. In addition, faster rates for reactions of aryl triflates versus those for reactions of aryl bromides allow the α-arylations of aryl triflates to be conducted at lower temperatures, and this lower temperature improves enantioselectivity. Finally, studies that compare the enantioselectivities of catalytic reactions to those of stoichiometric reactions of isolated [(segphos)Pd(Ar)(Br)], [(segphos)Pd(Ar)(I)], and [(segphos)Ni(C 6H4-4-CN)Br] suggest that catalyst decomposition affects enantioselectivity.
- Liao, Xuebin,Weng, Zhiqiang,Hartwig, John F.
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p. 195 - 200
(2008/09/21)
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- Carbopalladation of nitriles: Synthesis of benzocyclic ketones and cyclopentenones via Pd-catalyzed cyclization of ω-(2-iodoaryl)alkanenitriles and related compounds
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An efficient procedure for the synthesis of 2,2-disubstituted benzocyclic ketones by intramolecular carbopalladation of nitriles has been developed. The cyclization of substituted 3-(2-iodoaryl)-propanenitriles affords indanones in high yields. The reaction is compatible with a wide variety of functional groups. This methodology has been extended to the synthesis of tetralones and cyclopentenones.
- Pletnev, Alexandre A.,Larock, Richard C.
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p. 9428 - 9438
(2007/10/03)
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- REDUCTION ELECTROCHIMIQUE DES DERIVES CARBONYLES INSATURES IX. INDANONES ET TETRALONES: ELECTROLYSES MIXTES EN PRESENCE D'ELECTROPHILES
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It is shown that activated cyclic carbonyl compounds, such as tetralones and indanones, can behave in a particular manner when they are reduced in presence of electrophiles.Two classes of electrophiles were chosen: alkyl halides and carbon dioxide.The reactivity (alkylation and carboxylation) often depends on the nature of the activated ketone used as a substrate.
- Moing, Armelle Orliac-Le,Delaunay, Jacques,Lebouc, Alain,Simonet, Jacques
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p. 4483 - 4494
(2007/10/02)
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