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Enantioselective and Enantiospecific Transition-Metal-Catalyzed Cross-Coupling Reactions of Organometallic Reagents To Construct C-C Bonds.

Cherney AH, Kadunce NT, Reisman SE - Chem. Rev. (2015)

View Article: PubMed Central - PubMed

Affiliation: The Warren and Katharine Schlinger Laboratory for Chemistry and Chemical Engineering, Division of Chemistry and Chemical Engineering, California Institute of Technology , Pasadena, California 91125, United States.

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The alkylradical can then combine with a chiral Ni complex toform a Ni species that can reductively eliminate thedesired product... The resulting Ni can be reduced by Ir to complete both catalytic cycles... Theearliest example of an enantioselective transition-metal-catalyzedcross-coupling reaction between an alkyl electrophile and an organomagnesiumreagent was disclosed by Kumada and co-workers in 1977, the resultof a surprising alkyl group isomerization observed during the couplingbetween homoallylic halide and PhMgBr (Scheme 4)... The previous examples of Ni-catalyzed stereoconvergentNegishicross-coupling reactions from the Fu laboratory have focused on theuse of activated secondary electrophiles; in 2014, they reported thecoupling between α-halo sulfonamides and arylzincreagents (Figures 19b)... Because sulfonyl groups do not significantlystabilize α-radicals, can be considered as anunactivated electrophile... Key to this transformation was the insightthat a “transmetalation first” mechanism could be operative,and that organonickel complex might undergo migratoryinsertion faster than oxidative addition of the alkyl halide electrophile.This theory was validated in the Ni-catalyzed asymmetric cascade cyclization/cross-couplingreaction between arylborane and several simple alkylbromides, in which heterocyclic products were obtainedin excellent ee... One approach to generating enantioenriched productsthrough transition-metal-catalyzed alkyl cross-coupling reactionsis to perform desymmetrization reactions of meso-compounds.In this case, the C(sp)-hybridized carbon at the siteof C–C bond formation is not necessarily stereogenic; instead,the C–C bond formation is used to break symmetry through acatalyst-controlled process, giving rise to a molecule with centrochirality.Most of the work in this area has focused on the desymmetrizationof meso-electrophiles; however, some researchershave investigated the desymmetrization of meso-bisorganometallicreagents or processes that involve desymmetrization by C–Hfunctionalization... Trifluoroborate was found to undergo Pd-catalyzed cross-coupling with chlorobenzeneto give in high yield and es, and with inversionof stereochemistry (Figure 43)... The use of the bulky Buchwald ligand XPhos was found to prevent the formation of products resulting from β-hydrideelimination or isomerization... In 1997, RajanBabu and co-workers disclosed an enantioselectiveNi/-catalyzed alkylation of acyclic diphenylallylether (Scheme 27a)... Methyl ethers werefound to provide better results than phenyl ethers, whereas EtMgBrdelivered slightly higher ee than MeMgBr... The majority of Cu-catalyzed asymmetricallylic substitution reactionsof alkyl Grignard reagents employ nonstereogenic allyl electrophiles.High enantioinduction arises from catalyst differentiation of thepro-chiral faces of the substrate... Following a reportfrom Nicolaou and co-workers describing the use of chiral ligandsto enhance the atropodiastereoselectivity of a Pd-catalyzed Suzuki–Miyauraaryl–aryl cross-coupling in the synthesis of vancomycin, the laboratories of Cammidge and Buchwald independentlydisclosed enantioselective reactions to prepare simple biaryl systems.In 2000, Cammidge and co-workers reported the Pd-catalyzed couplingof boronate and iodonaphthalene ,delivering in 85% ee when was usedas a chiral ligand (Scheme 50)... Building on reportsfrom Yu and co-workers that chiral monoprotected amino acids werecompetent ligands for asymmetric C–H activation/cross-couplingtechniques, the authors subjected and PhB(OH)2 to Pd(OAc)2 and a seriesof different amino acid-derived ligands (Scheme 59)... Boc-l-Val-OH was found to effect formation of withexcellent enantioinduction and a minimal amount of the bisarylatedproduct.

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Atroposelectivering openings of dinaphthothiophene.
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fig92: Atroposelectivering openings of dinaphthothiophene.

Mentions: Exploiting the ability of Ni to insert into the C–Sbondof benzothiophene, Hayashi and co-workers explored the Ni-catalyzedKumada–Corriu coupling of 474 with aryl Grignardreagents to give enantioenriched biaryl thiols (Figure 92a).351,352 Dinaphthothiophene (474) is generally considered tobe an achiral compound because of the low barrier to flipping aboutthe axial axis of symmetry. When PHOX ligand L52 wasemployed, the Ni-catalyzed ring-opening/cross-coupling proceeded inhigh yield and ee. The atroposelectivity was strongly influenced bythe identity of the Grignard reagent; alkylmagnesium reagents reactedwith poor selectivity. On the basis of this observation, the authorspropose that the reaction proceeds by a DYKAT of the rapidly equilibratingoxidative addition products (M)-476 and(P)-476, in which the transmetalationstep sets the axial chirality. The reaction could also be extendedto dibenzothiophene coupling partners to generate axially chiral biphenylproducts. Despite efforts to improve the selectivity of the reactionbetween 474 and alkyl Grignard reagents, the best conditionsidentified to date, which utilize chiral phosphine L106, deliver 477 with only moderate enantioselectivity(Figure 92b).


Enantioselective and Enantiospecific Transition-Metal-Catalyzed Cross-Coupling Reactions of Organometallic Reagents To Construct C-C Bonds.

Cherney AH, Kadunce NT, Reisman SE - Chem. Rev. (2015)

Atroposelectivering openings of dinaphthothiophene.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4566132&req=5

fig92: Atroposelectivering openings of dinaphthothiophene.
Mentions: Exploiting the ability of Ni to insert into the C–Sbondof benzothiophene, Hayashi and co-workers explored the Ni-catalyzedKumada–Corriu coupling of 474 with aryl Grignardreagents to give enantioenriched biaryl thiols (Figure 92a).351,352 Dinaphthothiophene (474) is generally considered tobe an achiral compound because of the low barrier to flipping aboutthe axial axis of symmetry. When PHOX ligand L52 wasemployed, the Ni-catalyzed ring-opening/cross-coupling proceeded inhigh yield and ee. The atroposelectivity was strongly influenced bythe identity of the Grignard reagent; alkylmagnesium reagents reactedwith poor selectivity. On the basis of this observation, the authorspropose that the reaction proceeds by a DYKAT of the rapidly equilibratingoxidative addition products (M)-476 and(P)-476, in which the transmetalationstep sets the axial chirality. The reaction could also be extendedto dibenzothiophene coupling partners to generate axially chiral biphenylproducts. Despite efforts to improve the selectivity of the reactionbetween 474 and alkyl Grignard reagents, the best conditionsidentified to date, which utilize chiral phosphine L106, deliver 477 with only moderate enantioselectivity(Figure 92b).

View Article: PubMed Central - PubMed

Affiliation: The Warren and Katharine Schlinger Laboratory for Chemistry and Chemical Engineering, Division of Chemistry and Chemical Engineering, California Institute of Technology , Pasadena, California 91125, United States.

AUTOMATICALLY GENERATED EXCERPT
Please rate it.

The alkylradical can then combine with a chiral Ni complex toform a Ni species that can reductively eliminate thedesired product... The resulting Ni can be reduced by Ir to complete both catalytic cycles... Theearliest example of an enantioselective transition-metal-catalyzedcross-coupling reaction between an alkyl electrophile and an organomagnesiumreagent was disclosed by Kumada and co-workers in 1977, the resultof a surprising alkyl group isomerization observed during the couplingbetween homoallylic halide and PhMgBr (Scheme 4)... The previous examples of Ni-catalyzed stereoconvergentNegishicross-coupling reactions from the Fu laboratory have focused on theuse of activated secondary electrophiles; in 2014, they reported thecoupling between α-halo sulfonamides and arylzincreagents (Figures 19b)... Because sulfonyl groups do not significantlystabilize α-radicals, can be considered as anunactivated electrophile... Key to this transformation was the insightthat a “transmetalation first” mechanism could be operative,and that organonickel complex might undergo migratoryinsertion faster than oxidative addition of the alkyl halide electrophile.This theory was validated in the Ni-catalyzed asymmetric cascade cyclization/cross-couplingreaction between arylborane and several simple alkylbromides, in which heterocyclic products were obtainedin excellent ee... One approach to generating enantioenriched productsthrough transition-metal-catalyzed alkyl cross-coupling reactionsis to perform desymmetrization reactions of meso-compounds.In this case, the C(sp)-hybridized carbon at the siteof C–C bond formation is not necessarily stereogenic; instead,the C–C bond formation is used to break symmetry through acatalyst-controlled process, giving rise to a molecule with centrochirality.Most of the work in this area has focused on the desymmetrizationof meso-electrophiles; however, some researchershave investigated the desymmetrization of meso-bisorganometallicreagents or processes that involve desymmetrization by C–Hfunctionalization... Trifluoroborate was found to undergo Pd-catalyzed cross-coupling with chlorobenzeneto give in high yield and es, and with inversionof stereochemistry (Figure 43)... The use of the bulky Buchwald ligand XPhos was found to prevent the formation of products resulting from β-hydrideelimination or isomerization... In 1997, RajanBabu and co-workers disclosed an enantioselectiveNi/-catalyzed alkylation of acyclic diphenylallylether (Scheme 27a)... Methyl ethers werefound to provide better results than phenyl ethers, whereas EtMgBrdelivered slightly higher ee than MeMgBr... The majority of Cu-catalyzed asymmetricallylic substitution reactionsof alkyl Grignard reagents employ nonstereogenic allyl electrophiles.High enantioinduction arises from catalyst differentiation of thepro-chiral faces of the substrate... Following a reportfrom Nicolaou and co-workers describing the use of chiral ligandsto enhance the atropodiastereoselectivity of a Pd-catalyzed Suzuki–Miyauraaryl–aryl cross-coupling in the synthesis of vancomycin, the laboratories of Cammidge and Buchwald independentlydisclosed enantioselective reactions to prepare simple biaryl systems.In 2000, Cammidge and co-workers reported the Pd-catalyzed couplingof boronate and iodonaphthalene ,delivering in 85% ee when was usedas a chiral ligand (Scheme 50)... Building on reportsfrom Yu and co-workers that chiral monoprotected amino acids werecompetent ligands for asymmetric C–H activation/cross-couplingtechniques, the authors subjected and PhB(OH)2 to Pd(OAc)2 and a seriesof different amino acid-derived ligands (Scheme 59)... Boc-l-Val-OH was found to effect formation of withexcellent enantioinduction and a minimal amount of the bisarylatedproduct.

No MeSH data available.