Cu‐Catalyzed Alkylative Carboxylation of Ynamides with Dialkylzinc Reagents and Carbon Dioxide

Takimoto, Masanori; Gholap, Sandeep Suryabhan; Hou, Zhaomin

doi:10.1002/chem.201502774

Cited by 61 publications

(26 citation statements)

References 101 publications

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“…We recently demonstrated that [(IPr)CuCl] (IPr=1,3‐bis(2,6‐diisopropenyl)imidazol‐2‐ylidene) could act as an efficient catalyst for the carbozincation of ynamides with dialkylzinc reagents . Fortunately, in our initial study, we found that it could also be used for allenamide substrates.…”

Section: Resultsmentioning

confidence: 99%

“…In recent years, N‐heterocyclic carbene (NHC)–copper complexes have been proved to be excellent catalysts for the carboxylation of various organic compounds with CO 2 to give the corresponding carboxylic acids or their derivatives . As part of our studies on the use of CO 2 as a building block for organic synthesis, we recently reported the NHC‐copper‐catalyzed alkylative carboxylation of ynamides with CO 2 and dialkylzinc reagents, which afforded the corresponding α,β‐dehydro‐α‐amino acid derivatives .…”

Section: Introductionmentioning

confidence: 99%

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Regioselective Alkylative Carboxylation of Allenamides with Carbon Dioxide and Dialkylzinc Reagents Catalyzed by an N‐Heterocyclic Carbene–Copper Complex

Gholap

Takimoto

Hou

2016

Chemistry A European J

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The alkylative carboxylation of allenamide catalyzed by an N-heterocyclic carbene (NHC)-copper(I) complex [(IPr)CuCl] with CO2 and dialkylzinc reagents was investigated. The reaction of allenamides with dialkylzinc reagents (1.5 equiv) and CO2 (1 atm.) proceeded smoothly in the presence of a catalytic quantity of [(IPr)CuCl] to afford (Z)-α,β-dehydro-β-amino acid esters in good yields. The reaction is regioselective, with the alkyl group introduced onto the less hindered γ-carbon, and the carboxyl group introduced onto the β-carbon atom of the allenamides. The first step of the reaction was alkylative zincation of the allenamides to give an alkenylzinc intermediate followed by nucleophilic addition to CO2 . A variety of cyclic and acyclic allenamides were found to be applicable to this transformation. Dialkylzinc reagents bearing β-hydrogen atoms, such as Et2 Zn or Bu2 Zn, also gave the corresponding alkylative carboxylation products without β-hydride elimination. The present methodology provides an easy route to alkyl-substituted α,β-dehydro-β-amino acid ester derivatives under mild reaction conditions with high regio- and stereoselectivtiy.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Regioselective Alkylative Carboxylation of Allenamides with Carbon Dioxide and Dialkylzinc Reagents Catalyzed by an N‐Heterocyclic Carbene–Copper Complex

Gholap

Takimoto

Hou

2016

Chemistry A European J

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“…In 2015, Takimoto, Gholap, and Hou reported the carboxylation of ynamides by using a Cu−NHC complex (NHC= N ‐heterocyclic carbene) and a stoichiometric amount of ZnR 2 under 1 atm CO 2 pressure (Scheme ) . Various substituents (R 1 and R 2 ) and zinc reagents (ZnMe 2 , ZnEt 2 , and ZnBu 2 ) were successfully employed in this carboxylation process.…”

Section: Transition‐metal‐catalyzed Hydrocarboxylation Reactionsmentioning

confidence: 99%

“…In 2015, Takimoto, Gholap, and Hou reported the carboxylation of ynamides by using aC u ÀNHC complex (NHC = N-heterocyclic carbene) andas toichiometrica mount of ZnR 2 under 1atm CO 2 pressure (Scheme 24). [26] Various substituents (R 1 and R 2 )a nd zinc reagents (ZnMe 2 ,Z nEt 2 ,a nd ZnBu 2 )w ere successfully employed in this carboxylation process. The reaction began with the carbocupration of ynamides with CuR, which was generated from (IPr)CuCl and ZnR 2 .T he regioselectivity was controlled by coordination of the carbonyl oxygen atom to the copper center.S ubsequently,C O 2 could be insertedi nto the CÀCu bond to afford the copper carboxylate.…”

Section: Transition-metal-catalyzed Hydrocarboxylation Reactionsmentioning

confidence: 99%

Syntheses of α‐Amino Acids by Using CO₂ as a C1 Source

Mita

Sato

2019

Chemistry An Asian Journal

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The incorporation of CO2 into organic compounds is currently one of the most active research topics in organic chemistry, because CO2 is an abundant, inexpensive, nontoxic, and renewable C1 source. However, CO2 is also a thermodynamically stable and kinetically inert gaseous compound, and as such, special strategies are required to activate CO2 and incorporate it into organic compounds. In particular, because the carbon atom adjacent to the nitrogen atom of amine derivatives is positively charged, umpolung carboxylation, which is a difficult chemical process, should be considered for the production of α‐amino acids by using CO2. In this Minireview, we summarize recent synthetic methods for α‐amino acids that use CO2 as a carboxylic acid unit.

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“…12 In addition, Hou's group developed Cu-catalyzed alkylative carboxylation of ynamide that gives α-carboxylated products. 13 Taking these reports into account, the α-selectivity would be induced by steric repulsion between a nickel complex and carbon substitution at the β-position and/or by interaction between a nickel complex and a substituent of nitrogen at the addition step of a nickel hydride species to ynamide. In summary, we have described a nickel-catalyzed regioselective hydrocarboxylation of ynamide with CO 2 and H 2 O in the presence of Zn/MgBr 2 under mild conditions (0 °C).…”

Section: Nickel-catalyzed Hydrocarboxylation Of Ynamides With Comentioning

confidence: 99%

Nickel-catalyzed hydrocarboxylation of ynamides with CO₂ and H₂O: observation of unexpected regioselectivity

et al. 2017

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We describe the nickel-catalyzed hydrocarboxylation of ynamides with CO 2 and H 2 O to afford a variety of α-amino-α,β-unsaturated esters with high regioselectivities. Selective α-carboxylation of ynamide with this catalytic protocol is unexpected in view of the electronic bias of ynamide and is in sharp contrast to our previous study in which a stoichiometric amount of Ni(0) was used to form a β-carboxylated product exclusively. We revealed that this unexpected C−C bond formation was induced by the combination of Zn and MgBr 2 .Homogeneous nickel catalysis has emerged in the past few decades as a highly efficient tool for organic synthesis.1 The intrinsic chemical properties of some nickel catalysts to construct a C−C bond have been applied to incorporation of CO 2 , which is an abundant, non-toxic and renewable carbon source. 2 Especially, reactions using compounds bearing a C−C double bond or triple bond as a coupling partner of CO 2 enable transformation of these building blocks into carboxylic acid derivatives without prefunctionalization such as halogenation or metalation. [3][4][5] Since all carbons constituting an unsaturated bond are potentially reactive, controlling the regioselectivity is a common concern of these promising reactions employing CO 2 . Recently, Martin's group has developed regioselective hydrocarboxylation of alkyl aryl acetylenes with CO 2 employing alcohol as a proton source. 4f They speculated that an equilibrium would exist between two possible nickelalactones derived from alkyne and CO 2 and that steric repulsion between an alkyl group and alcohol would be a key factor for preferential formation of carboxylic acid A behind B (Scheme 1). Their proposed mechanism let us assume another strategy for nickel-catalyzed regioselective hydrocarboxylation of a C−C triple bond with CO 2 in which the selectivity would be engendered by taking advantage of an electronic factor. Herein, we report a nickel-catalyzed regioselective hydrocarboxylation of ynamide, which is known to have an electronic bias on the C−C triple bond, by use of H 2 O and CO 2 .6 Consequently, we observed an interesting selectivity switching triggered by additives. Scheme 2. Our previous work: Nickel-mediated hydrocarboxylation of ynamide with CO2We previously described a nickel-mediated regioselective synthesis of functionalized β-amino-α,β-unsaturated esters from ynamides 1 and CO 2 .7 The selectivity was controlled by a regioselective oxidative cyclization step in which a negative β-carbon of an ynamide forms a C−C bond with CO 2 on Ni(0) (Scheme 2). The resulting β-carboxylated products were shown to be precursors of enantio-enriched β-amino acid derivatives by conducting Rh-catalyzed asymmetric hydrogenation. As a next step, we commenced to develop a regioselective catalytic hydrocarboxylation of ynamides. Recently, Sakaki and Tsuji et al. reported a nickel-catalyzed double carboxylation of alkyne by the use of CO 2 in the presence of Zn/MgBr 2 as reducing agents. 4g We applied their reaction conditions to catalytic ...

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Cu‐Catalyzed Alkylative Carboxylation of Ynamides with Dialkylzinc Reagents and Carbon Dioxide

Cited by 61 publications

References 101 publications

Regioselective Alkylative Carboxylation of Allenamides with Carbon Dioxide and Dialkylzinc Reagents Catalyzed by an N‐Heterocyclic Carbene–Copper Complex

Regioselective Alkylative Carboxylation of Allenamides with Carbon Dioxide and Dialkylzinc Reagents Catalyzed by an N‐Heterocyclic Carbene–Copper Complex

Syntheses of α‐Amino Acids by Using CO₂ as a C1 Source

Nickel-catalyzed hydrocarboxylation of ynamides with CO₂ and H₂O: observation of unexpected regioselectivity

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Cu‐Catalyzed Alkylative Carboxylation of Ynamides with Dialkylzinc Reagents and Carbon Dioxide

Cited by 61 publications

References 101 publications

Regioselective Alkylative Carboxylation of Allenamides with Carbon Dioxide and Dialkylzinc Reagents Catalyzed by an N‐Heterocyclic Carbene–Copper Complex

Regioselective Alkylative Carboxylation of Allenamides with Carbon Dioxide and Dialkylzinc Reagents Catalyzed by an N‐Heterocyclic Carbene–Copper Complex

Syntheses of α‐Amino Acids by Using CO2 as a C1 Source

Nickel-catalyzed hydrocarboxylation of ynamides with CO2 and H2O: observation of unexpected regioselectivity

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Syntheses of α‐Amino Acids by Using CO₂ as a C1 Source

Nickel-catalyzed hydrocarboxylation of ynamides with CO₂ and H₂O: observation of unexpected regioselectivity