Cross Coupling of Acyl and Aminyl Radicals: Direct Synthesis of Amides Catalyzed by Bu<sub>4</sub>NI with TBHP as an Oxidant

Liu, Zhaojun; Zhang, Jie; Chen, Shulin; Shi, Erbo; Xu, Yungen; Wan, Xiaobing

doi:10.1002/anie.201108763

Cited by 375 publications

(121 citation statements)

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“…[6] The transformation of aldehydes into esters and amides in one step is an attractive goal that has been pursued using precious-metal catalysts, [7] base-metal catalysts with strong oxidants, [8] and N-heterocyclic carbene (NHC) catalysis.…”

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“…However, when using the same method at slightly elevated temperatures (40 8C), amide bond formation was observed using aniline nucleophiles (Scheme 3). Thus, we can convert aldehydes into amides using base-metal catalysis without relying on highly reactive reagents, such as peroxides [8] or aryl azides. [16] Under these conditions, aldehydes containing electron-donating (7 b, 93 %) or -withdrawing (7 c, 97 %) groups reacted efficiently, as well as aldehydes that would be sensitive to peroxide oxidants (7 d, 91 %).…”

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Nickel‐Catalyzed Dehydrogenative Cross‐Coupling: Direct Transformation of Aldehydes into Esters and Amides

Whittaker

Dong

2014

Angewandte Chemie

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By exploring a new mode of nickel-catalyzed crosscoupling, a method to directly transform both aromatic and aliphatic aldehydes into either esters or amides has been developed. The success of this oxidative coupling depends on the appropriate choice of catalyst and organic oxidant, including the use of either a,a,a-trifluoroacetophenone or excess aldehyde. Mechanistic data that supports a catalytic cycle involving oxidative addition into the aldehyde C À H bond is also presented.Developing nickel catalysts for the selective oxidation of CÀH bonds is an emerging strategy that overcomes the need for precious metals and enables new transformations.[1] Our laboratory has previously focused on the oxidation of aldehydes under Rh, Ru, and Co catalysis.[2] Inspired by the promise of base metals, we considered that Ni-catalyzed cross-couplings of aldehydes could be classified into three general types: redox-neutral, reductive, and oxidative ( Figure 1). For example, Ogoshis cross-coupling between two aldehydes is a redox-neutral method that generates ester bonds.[3] In comparison, reductive coupling reactions generate carbon-carbon bonds in the presence of an external reductant (e.g., Et 2 Zn).[4] A complementary Ni-catalyzed cross-coupling in the presence of an external oxidant, however, represents an undeveloped mode of reactivity that warrants study.[5] Herein, we showcase a unified approach for transforming aldehyde CÀH bonds into both CÀO and CÀN bonds using Ni-catalyzed dehydrogenative cross-couplings. [6] The transformation of aldehydes into esters and amides in one step is an attractive goal that has been pursued using precious-metal catalysts, [7] base-metal catalysts with strong oxidants, [8] and N-heterocyclic carbene (NHC) catalysis.[9]Whereas these methods are promising, a method that couples aromatic and aliphatic aldehydes with alcohols, anilines, and amines has yet to be achieved. Towards addressing this challenge, we chose to examine carbonyl compounds as mild oxidants by hydrogen transfer.[10]Our initial studies focused on cross-coupling benzaldehyde (1 a) and 2-propanol (2 a) in the presence of various hydrogen acceptors. We discovered that NHC ligands in 1,4-dioxane produced the most promising results (Scheme 1). [11] In the absence of any Ni salts, we observed no reactivity. However, in the presence of [Ni(cod) 2 ] with benzaldehyde as both the substrate and hydrogen acceptor, we observed the formation of the desired ester 4 a and Tishchenko homodimer 5 a in a 5.9:1 ratio. To suppress the Tishchenko pathway, we sought an acceptor that undergoes reduction faster than benzaldehyde (1 a). Whereas the addition of acetone (3 a) and cyclobutanone (3 b) decreased the rate of the desired crosscoupling, both benzophenone (3 c) and a,a,a-trifluoroacetophenone (3 d) showed a remarkable enhancement in rate and selectivity for 4 a. As a result, we were able to use equimolar quantities of the coupling partners and 1

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Nickel‐Catalyzed Dehydrogenative Cross‐Coupling: Direct Transformation of Aldehydes into Esters and Amides

Whittaker

Dong

2014

Angewandte Chemie

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“…Iodide was initially oxidized by TBHP to Na[IO] − , which was further oxidized to a key intermediate hypoiodite Na[IO 2 ] − (A) with one more equivalent of TBHP [33,34]. The oxidative addition of 2 at the α-position by A would give a key β-diester intermediate B, which readily experienced substitution by 1 to give the α-oxybenzoylation product 4 under mild conditions (60°C), releasing the catalyst precursor Na[IO] − .…”

Section: Resultsmentioning

confidence: 99%

Temperature-controlled NaI-mediated α-oxybenzoylation or oxyacylation–decarboxylation reactions of dimethyl malonate with carboxylic acids

Mao

Liu

et al. 2015

Catalysis Communications

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“…Other solvents studied, such as DMF and DMSO, resulted in meaningless yields. Other oxidants were also employed, and 3a was not detected (Table 1, entries [14][15][16][17]. Besides, experiments also demonstrated that no 3a was formed in the absence of catalyst or oxidant (Table 1, entries 8 and 18).…”

Section: Resultsmentioning

confidence: 99%

Copper-catalyzed oxidative coupling of carboxylic acids with formamides for the synthesis of α,β-unsaturated amides

Li¹,

Pan²,

Cheng³

et al. 2013

Tetrahedron Letters

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Cross Coupling of Acyl and Aminyl Radicals: Direct Synthesis of Amides Catalyzed by Bu₄NI with TBHP as an Oxidant

Abstract: Scheme 4. Scope of the reaction with aryl aldehydes. Scheme 5. Scope of the reaction with other aromatic aldehydes. Scheme 6. Scope of the reaction with N,N-disubstituted formamides. 2.0 mL of ethyl acetate was used for 9 f. N.O = not obtained Angewandte Chemie 3233

Cited by 375 publications

References 145 publications

Nickel‐Catalyzed Dehydrogenative Cross‐Coupling: Direct Transformation of Aldehydes into Esters and Amides

Nickel‐Catalyzed Dehydrogenative Cross‐Coupling: Direct Transformation of Aldehydes into Esters and Amides

Temperature-controlled NaI-mediated α-oxybenzoylation or oxyacylation–decarboxylation reactions of dimethyl malonate with carboxylic acids

Copper-catalyzed oxidative coupling of carboxylic acids with formamides for the synthesis of α,β-unsaturated amides

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Cross Coupling of Acyl and Aminyl Radicals: Direct Synthesis of Amides Catalyzed by Bu4NI with TBHP as an Oxidant

Abstract: Scheme 4. Scope of the reaction with aryl aldehydes. Scheme 5. Scope of the reaction with other aromatic aldehydes. Scheme 6. Scope of the reaction with N,N-disubstituted formamides. 2.0 mL of ethyl acetate was used for 9 f. N.O = not obtained Angewandte Chemie 3233

Cited by 375 publications

References 145 publications

Nickel‐Catalyzed Dehydrogenative Cross‐Coupling: Direct Transformation of Aldehydes into Esters and Amides

Nickel‐Catalyzed Dehydrogenative Cross‐Coupling: Direct Transformation of Aldehydes into Esters and Amides

Temperature-controlled NaI-mediated α-oxybenzoylation or oxyacylation–decarboxylation reactions of dimethyl malonate with carboxylic acids

Copper-catalyzed oxidative coupling of carboxylic acids with formamides for the synthesis of α,β-unsaturated amides

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Cross Coupling of Acyl and Aminyl Radicals: Direct Synthesis of Amides Catalyzed by Bu₄NI with TBHP as an Oxidant