Merging Photoredox with Copper Catalysis: Decarboxylative Alkynylation of α-Amino Acid Derivatives

Zhang, Hao; Zhang, Pengxiang; Jiang, Min; Yang, Haijun; Fu, Hua

doi:10.1021/acs.orglett.6b03888

Cited by 88 publications

(40 citation statements)

References 97 publications

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“…For example, the oxidative decarboxylation of aliphatic acids to form alkyl radicals with subsequent capture by alkynyl electrophiles. [14] Concurrent with these studies, Fu reported on the coupling of terminal alkynes with α-amino NHP esters [15] and Baran reported on the coupling of N -hydroxytetrachlorophthalimide (TCNHPI) esters with alkynylzinc or magnesium reagents. [16] Our proposed approach would avoid the need for organometallic reagents and the more expensive TCNHPI [17] without being limited to α-amino acid derivatives.…”

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confidence: 99%

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Reductive Decarboxylative Alkynylation of N‐Hydroxyphthalimide Esters with Bromoalkynes

2017

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A new method for the synthesis of terminal and internal alkynes from the nickel-catalyzed decarboxylative coupling of N-hydroxyphthalimide esters (NHP esters) and bromoalkynes is presented. This reductive cross-electrophile coupling is the first to use a C(sp)-X electrophile, and appears to proceed via an alkynylnickel intermediate. The internal alkyne products are obtained in 41–95% yield without the need for a photocatalyst, light, or strong oxidant. The reaction displays a broad scope of carboxylic acid and alkyne coupling partners and can tolerate an array of functional groups including a carbamate N-H, halogen, nitrile, olefin, ketone, and ester. Mechanistic studies suggest that this process does not involve an alkynylmanganese reagent and involves nickel-mediated bond formation.

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confidence: 99%

“…[16] Our proposed approach would avoid the need for organometallic reagents and the more expensive TCNHPI [17] without being limited to α-amino acid derivatives. [15] Although this approach would use alkyne electrophiles, bromoalkynes [7] are more easily prepared than ethynylbenziodoxolones [18] or alkynyl sulfones. [14a–c] …”

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confidence: 99%

Reductive Decarboxylative Alkynylation of N‐Hydroxyphthalimide Esters with Bromoalkynes

2017

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“…However, acetophenone itself was partially consumed by transamination to 1phenethylamine (entry 25). α,β-Unsaturated ketones (entries [14][15][16][17][18][19][20][21][22][23][24], in particular the derivatives of 2-cyclohexen-1-one (entries 18-21 and 23), are among the most active organocatalysts: for instance, 2 a was produced in > 85 % yield within 4 h by using isophorone or 3-phenyl-2-cyclohexen-1-one. These catalysts increased the amine yield at least by a factor 10 compared to the thermal reaction.…”

Section: Decarboxylation Of Amino Acids To Aminesmentioning

confidence: 99%

“…[18] Decarboxylation is also a step in several photoredox-based carbon-carbon bondforming reactions using protected amino acids as a coupling partner. [19][20][21][22][23] Transition metal-free approaches for amino acid decarboxylation have been reported as well. For instance, the formation of biogenic amines in food and beverages is related either to the presence of carbohydrate-or lipid-derived reactive carbonyl compounds, [24,25] or to the action of amino acid decarboxylases containing pyridoxal 5'-phosphate (PLP) or a pyruvoyl group as cofactor.…”

Section: Introductionmentioning

confidence: 99%

Organocatalytic Decarboxylation of Amino Acids as a Route to Bio‐based Amines and Amides

2019

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Amino acids obtained by fermentation or recovered from protein waste hydrolysates represent an excellent renewable resource for the production of bio‐based chemicals. In an attempt to recycle both carbon and nitrogen, we report here on a chemocatalytic, metal‐free approach for decarboxylation of amino acids, thereby providing a direct access to primary amines. In the presence of a carbonyl compound the amino acid is temporarily trapped into a Schiff base, from which the elimination of CO2 may proceed more easily. After evaluating different types of aldehydes and ketones on their activity at low catalyst loadings (≤5 mol%), isophorone was identified as powerful organocatalyst under mild conditions. After optimisation many amino acids with a neutral side chain were converted in 28–99 % yield in 2‐propanol at 150 °C. When the reaction is performed in DMF, the amine is susceptible to N‐formylation. This consecutive reaction is catalysed by the acidity of the amino acid reactant itself. In this way, many amino acids were efficiently transformed to the corresponding formamides in a one‐pot catalytic system.

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“…Photoredox chemistry has been applied to generate alkyl radicals from alkyl redox-active esters for subsequent Michael addition reactions 35,36 , while a similar approach for decarboxylative alkynylation of α -amino acid derivatives has been used 37 . In view of the difficulty in activating redox-active esters by metal amides, we envisioned a synergetic photoredox and metal catalysis for C-N coupling of redox-active esters with anilines (Fig.…”

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Decarboxylative C(sp3)–N cross-coupling via synergetic photoredox and copper catalysis

et al. 2018

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A mines are one of the most important structural motifs in pharmaceuticals, agrochemicals and organic materials 1,2 . Alkylation and reductive amination reactions are still commonly used to prepare and modify amines, and new methods derived from reductive amination, such as the borrowing hydrogen 3 strategy, have been reported [4][5][6][7] . Nevertheless, the most significant development in amine synthesis has been transition-metal-catalysed C-N coupling of aryl electrophiles (halides and pseudo halides) with amine nucleophiles [8][9][10][11] (Fig. 1a). The C-N coupling of alkyl electrophiles, however, is largely under-developed (Fig. 1a). A perceived difficulty is β -hydrogen elimination from a metal alkyl intermediate originated from oxidative addition of the alkyl electrophile, which has posed considerable challenges in analogous C-C crosscoupling of alkyl electrophiles [12][13][14] . Moreover, the product-yielding C(sp 3 )-N reductive elimination step is rarely demonstrated 15 . A notable exception is the light-induced, copper-catalysed C-N coupling of alkyl halides recently developed [16][17][18] . Nevertheless, the scope of amine nucleophiles is limited to carbazoles 16,18 and amides 17,19 . Alternative, formal C-N coupling of alkyl electrophiles via the addition of alkyl radicals to nitroarenes has been reported 20,21 .The group of Baran has recently trailblazed the use of redox-active esters derived from alkyl carboxylic acids as superior surrogates of alkyl halides in decarboxylative C-C cross-coupling reactions [22][23][24] . Extension to a decarboxylative carbon-heteroatom, particularly C-B bond formation has also been reported 19,[25][26][27][28][29] . The key attributes of alkyl carboxylic acids 30,31 are their unparalleled availability, stability and non-toxic nature, which are in stark contrast with alkyl halides, ketones and aldehydes. While several precedents of decarboxylative imidation 32 and amination 19,33 are known, they are limited to a narrow scope of very special substrates or intramolecular reactions. A general metal-catalysed decarboxylative C-N coupling of redox-active esters with anilines will provide valuable methodology for the synthesis of alkylated anilines (Fig. 1b), which requires alkyl halides and carbonyl compounds 6 as starting reagents using the currently standard methods of alkylation and reductive amination, respectively. Further foreseen advantages of such a decarboxylative amination include applicability to bulky primary and secondary alkyl groups and immunity to over-alkylation, both of which are major limitations of direct alkylation (Fig. 1b). Despite its conceptual simplicity and resemblance to decarboxylative C-C coupling, the intermolecular decarboxylative C-N coupling of redoxactive esters poses significant hurdles. The activation principle of redox-active esters originates from amide-bond synthesis; thus, amide formation can compete when amine nucleophiles are used. Moreover, decarboxylative C-C coupling reactions of redox-active esters were, until now, all init...

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Merging Photoredox with Copper Catalysis: Decarboxylative Alkynylation of α-Amino Acid Derivatives

Cited by 88 publications

References 97 publications

Reductive Decarboxylative Alkynylation of N‐Hydroxyphthalimide Esters with Bromoalkynes

Reductive Decarboxylative Alkynylation of N‐Hydroxyphthalimide Esters with Bromoalkynes

Organocatalytic Decarboxylation of Amino Acids as a Route to Bio‐based Amines and Amides

Decarboxylative C(sp3)–N cross-coupling via synergetic photoredox and copper catalysis

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