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COMMUNICATION Catalytic Ester and Amide To Catalytic Ester and Amide to Amine Interconversion: Nickel-Catalyzed Decarbonylative Amination of Esters and Amides by C−O and C−C Bond Activation Item Type Article Authors Yue, Huifeng; Guo, Lin; Liao, Hsuan-Hung; Cai, Yunfei; Zhu, Chen; Rueping, Magnus Citation Yue H, Guo L, Liao H-H, Cai Y, Zhu C, et al. (2017) Catalytic Ester and Amide to Amine Interconversion: Nickel-Catalyzed Decarbonylative Amination of Esters and Amides by C−O and C −C Bond Activation. Angewandte Chemie International Edition 56: 4282–4285. Available: http://dx.doi.org/10.1002/anie.201611819. Eprint version Post-print DOI 10.1002/anie.201611819 Publisher Wiley Journal Angewandte Chemie International Edition Rights This is the peer reviewed version of the following article: Catalytic Ester and Amide to Amine Interconversion: Nickel-Catalyzed Decarbonylative Amination of Esters and Amides by C-O and C-C Bond Activation, which has been published in final form at http:// doi.org/10.1002/anie.201611819. This article may be used for non-commercial purposes in accordance With Wiley Terms and Conditions for self-archiving. Download date 23/09/2021 09:53:43 Link to Item http://hdl.handle.net/10754/623218 COMMUNICATION Catalytic Ester and Amide to Amine Interconversion: Nickel- Catalyzed Decarbonylative Amination of Esters and Amides via C- O and C-C Bond Activation Huifeng Yue[a], Lin Guo[a], Hsuan-Hung Liao[a], Yunfei Cai[a], Chen Zhu[a], and Magnus Rueping[a,b]* Abstract: An efficient nickel catalyzed decarbonylative amination reaction of aryl and heteroaryl esters has been achieved for the first a) Schmidt reaction; Curtius, Hoffmann, Lossen rearrangement time. The new amination protocol allows the direct interconversion of esters and amides into the corresponding amines and represents a O Ar NH N 2 good alternative to classical rearrangements as well as cross Ar C Ar OH O or coupling reactions. Ar NHR b) Classical amide bond formations Aromatic amines are important synthetic building blocks in O O chemistry due to their application in the preparation of R'NH2 + HOR pharmaceuticals, biologically active molecules, natural products, Ar OR with/without catalyst Ar NHR' polymers, as well as functional materials.[1] Accordingly, the development of new methodologies to access these valuable c) New decarbonylative amination of carboxylic acid derivatives molecules continues to be of great importance in synthetic organic chemistry.[1] Conventionally, Pd-catalyzed Buchwald- C-N bond formation Hartwig reaction represents a valuable C(sp2)-N bond formation O [2] Ar NH method which makes a great contribution to this field. Although catalyst 2 Ar X or This work Pd is dominating the field, and a considerable number of X=OR amine Ar NHR'' powerful catalytic systems for the conversion of aryl (pseudo) X=NRR' halides into aromatic amines has been reported, recent efforts Direct Ester and Amide to Amine Interconversion are devoted to the disclosure of improved protocols based on non-precious metal catalysts. Particular attention has been Scheme 1. a) Classical carboxylic acid to amine interconversions via drawn to the use of inexpensive and earth abundant nickel rearrangements; b) Classical amide bond formations via ester amine coupling; catalysts,[3] along with easily available and versatile C(sp2)-O c) Direct transformation of esters or amides to amines. electrophiles.[4-8] Despite the advances in this field, it is still highly desirable to further explore different electrophilic coupling partners for metal catalyzed amination reactions with the aim of Amides are typically rather stable functional groups, part of developing protocols based on cheaper, more stable, and peptides and proteins and are less prone to hydrolysis, if readily available substrates. Considerable progress has been compared to ester derivatives. They can simply be prepared by achieved in metal catalyzed decarboxylative and reaction of esters with amines and many different protocols [13] decarbonylative cross coupling reactions using carboxylic acids including a recent nickel catalyzed protocol for the amide and derivatives.[9-12] formation have been described (Scheme 1b). However, to the best of our knowledge, metal catalyzed Given the enormous interest in efficient protocols for the C(sp2)-N bond formations via a decarbonylative process with preparation of amines and limitations associated with the carboxylic acid derivatives as substrates have not been realized classical rearrangement reactions, we became interested in before. Traditionally, acids or erster derivatives are transformed developing a direct catalytic amination of aryl and heteroaryl to amines following a multi-step sequences and involve classical esters, in which the ester moiety would be replaced by an amine rearrangements (Scheme 1a). yielding aromatic amines in a one step process (Scheme 1c). Herein, we report an unprecedented decarbonylative amination protocol for the direct interconversion of esters as well as amides to aryl amines (Scheme 1c). In order to prevent the [a] H. Yue, L. Guo, H.-H. Liao, Y. Cai, C, Zhu, Prof. Dr. M. Rueping undesired amide bond formation when reacting esters with Institute of Organic Chemistry RWTH Aachen University amines (Scheme 1b), we decided to apply imines as Landoltweg 1, D-52074 Aachen, Germany nucleophiles instead. This would also allow the further E-mail: [email protected] funtionalization as well as direct access to primary aromatic [b] Prof. Dr. M. Rueping amines. King Abdullah University of Science and Technology (KAUST) KAUST Catalysis Center (KCC), Thuwal, 23955-6900 (Saudi Therefore, our initial experiments in developing the new Arabia) decarbonylative amination started with phenyl naphthalene-2- E-mail: [email protected] carboxylate (1a) and commercially available benzophenone Supporting information for this article is given via a link at the end of imine (2) (Table 1). Among the different metals tested, nickel the document. complexes proved to be good catalysts for the decarbonylation. The nature of the ligand critically affected the efficiency of our COMMUNICATION transformation. No reaction occurred when IPr.HCl was applied significantly the yield (entries 14-15). Under the optimized as ligand (entry 1). The use of monodentate phosphine ligands reaction conditions the desired product was isolated in 87% yield such as P(n-Bu)3 and PCy3 gave also no desired product (entries upon acidic hydrolysis. A slightly lower yield (80%) was obtained . 2 and 3). with Ni(OAc)2 4H2O as catalyst (entry 18). Control experiments showed that no amination product was observed in the absence [a] Table 1. Optimization of the reaction conditions. of Ni(cod)2 or dcype ligand (entries 16-17). When secondary amines such as morpholine was used, aminolysis reaction of the O 1. Ni(cod)2 or Ni(OAc)2 Ligand ester substrate occurred, affording the undesired amide product NH2 OPh NH base, additive 4.[13] Other esters such as methyl and benzyl esters were not + Ph Ph 2. Acidic Hydrolysis suitable for this transformation which allows for a chemoselective amination of differently protected esters. 1a 2 3a Entry [Ni] Ligand Base Additive Yield (x mol%) (2 equiv.) (2 equiv.) (%)[b] Ph HN NH 2 2 1 Ni(cod)2 IPr·HCl (20) Cs2CO3 - 0 Ph n 2 Ni(cod)2 P Bu3 (20) Cs2CO3 - 0 O 3a, 87% 3 Ni(cod)2 PCy3 (20) Cs2CO3 - 0 Ni(cod)2/dcype after acidic hydrolysis OPh K3PO4, LiCl 4 Ni(cod)2 dcype (10) Cs2CO3 - 14 toluene (1 ml) 5 Ni(cod) dcypf (10) Cs CO - trace O 2 2 3 1a 170 °C, 48 h O 6 Ni(cod)2 dcype (20) Cs2CO3 - 17 3 N H N 7 Ni(cod)2 dcype (20) Li2CO3 - 21 O 4 8 Ni(cod)2 dcype (20) K2CO3 - 31 amide bond formation 9 Ni(cod)2 dcype (20) Na2CO3 - 31 10 Ni(cod)2 dcype (20) K3PO4 - 42 Scheme 2. Nickel catalyzed decarbonylative amination of naphthyl ester 1a. t 11 Ni(cod)2 dcype (20) NaO Bu - 0 [c] 12 Ni(cod)2 dcype (20) K3PO4 - 56 With the optimized reaction conditions in hand, the scope with [c] 13 Ni(cod)2 dcype (20) K3PO4 LiCl 63 respect to the aryl esters was subsequently examined (Table 2). [c,d] 14 Ni(cod)2 dcype (20) K3PO4 LiCl 84 The results show that a range of aromatic and heteroaromatic [c-e] esters bearing various substitution patterns were tolerated in this 15 Ni(cod)2 dcype (20) K3PO4 LiCl 87 newly developed ester to amine transformation, giving the [c-e] 16 Ni(cod)2 - K3PO4 LiCl 0 corresponding primary amines in moderate to high yields. As [c-e] 17 - dcype (20) K3PO4 LiCl 0 anticipated, naphthyl esters 1a-c underwent this decarbonylative [c-e] 18 Ni(OAc)2 dcype (20) K3PO4 - 80 amination protocol in good to high yields. Although protocols for [c-e] [f] the amination of C-OMe bond under nickel catalysis have been 19 Ni(OAc)2 dcype (20) K3PO4 Mn 63 reported,[4] we were pleased to find that methoxy groups are well [c-e] [g] 20 Ni(OAc)2 dcype (20) K3PO4 Et3SiH 77 tolerated in our amination protocol (3c and 3j). Furthermore, not only simple biphenyl ester gave the desired products (3e and 3f) [a] IPr·HCl = 1,3-bis(2,6- diisopropylphenyl)imidazolium chloride, dcype = 1,2- bis(dicyclohexylphosphino)-ethane, dcypf=1,1′-Bis(dicyclohexylphosphino) in good yields, but also a series of biphenyl ester derivatives ferrocene. Reaction conditions: phenyl naphthalene-2-carboxylate 1a (0.2 possessing fluoro (1g), trifluoromethyl (1h), or tertiary butyl mmol), benzophenone imine 2 (0.3 mmol), Ni(cod)2 (0.02 mmol), ligand (0.02 substituents (1i) efficiently underwent this transformation. Simple mmol or 0.04 mmol), base (0.4 mmol) in toluene (1 ml) at 160 °C, 12 h. [b] phenyl derivatives are more challenging substrates than π- Yield of isolated products. [c] benzophenone imine 2 (2 equiv.), K PO (3 3 4 extended systems.[3f] However, we were pleased to find that equiv.).
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