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COMMUNICATION Amide to Alkyne Interconversion Via a Nickel/Copper Amide to Alkyne Interconversion via a Nickel/Copper-Catalyzed Deamidative Cross-Coupling of Aryl and Alkenyl Amides Item Type Article Authors Srimontree, Watchara; Chatupheeraphat, Adisak; Liao, Hsuan- Hung; Rueping, Magnus Citation Srimontree W, Chatupheeraphat A, Liao H-H, Rueping M (2017) Amide to Alkyne Interconversion via a Nickel/Copper-Catalyzed Deamidative Cross-Coupling of Aryl and Alkenyl Amides. Organic Letters 19: 3091–3094. Available: http://dx.doi.org/10.1021/ acs.orglett.7b01194. Eprint version Post-print DOI 10.1021/acs.orglett.7b01194 Publisher American Chemical Society (ACS) Journal Organic Letters Rights This document is the Accepted Manuscript version of a Published Work that appeared in final form in Organic Letters, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see http://pubs.acs.org/doi/full/10.1021/ acs.orglett.7b01194. Download date 26/09/2021 00:50:12 Link to Item http://hdl.handle.net/10754/625096 COMMUNICATION Amide to Alkyne Interconversion via a Nickel/Copper Catalyzed Deamidative Cross-Coupling of Aryl and Akenyl Amides Watchara Srimontree, Adisak Chatupheeraphat, Hsuan-Hung Liao, and Magnus Rueping* Abstract: A nickel catalyzed deamidative cross-coupling reaction of amides with terminal alkynes as coupling partners was developed. Classical: This newly developed methodology allows the direct interconversion of amides to alkynes and enables a facile route for C(sp2)-C(sp) Pd or Ni / Cu R-X + Y FG R FG bond formations in a straightforward and mild fashion. base R = aryl, hetaryl, vinyl/ X = I, Br, Cl, OTf, OMe/ Y = H, Li, MgBr Transition metal catalyzed cross-coupling reactions represent one of the most successful domains in modern organic This work: - deamidative cross-coupling chemistry. Among the developed transformations, the - no base required Sonogashira reaction has emerged as one of the most - no alkali metal acetylide required straightforward and powerful methods to facilitate linkages O SiR'3 between carbon atoms.[1] Although this well-known reaction NR2 shows superior ability to incorporate alkynyl units into organic Ar previously Ar molecules and found applications in industrial and laboratory not known + H SiR'3 O settings, the electrophilic coupling partners for the Sonogashira SiR'3 reactions are often limited to aryl and vinyl halides. Recently, Ar' NR2 Ar' increasing emphasis on the development of environmental friendly synthetic protocols has stimulated research aimed at finding alternative cross-coupling partners, which avoid the Main challenges: undesired byproducts formation corrosive halide-containing waste production in transition metal OH catalyzed reactions. The establishment of decarbonylative O transformations[2] making use of carboxylic acids, anhydrides, R' Si SiR' Ar SiR' 3 3 Ar 3 acid chlorides, esters and amides is significant in realizing this SiR'3 SiR' concept. With these considerations in mind, our attention was 3 Glaser-Hay homocoupling drawn to the cross coupling reaction of amide derivatives with ketone formation overaddition silylated acetylenes as nucleophilic coupling partners. If Scheme 1. Cross-coupling alkynylation reactions. successful, this protocol would allow the synthesis of alkynes which are versatile intermediates in organic synthesis and important structural motifs of various biologically active Given the considerations above, we started to investigate a molecules.[3] Beside their capacity to undergo subsequent deamidative cross-coupling reaction with amide 1a and transformations,[3] silylated alkynes can undergo (triisopropylsilyl)acetylene (2a) as reaction partners (Table 1). protodesilylation to afford terminal alkynes which hold great Among the different metal catalysts tested nickel complexes[7-11] potential for further functional group interconversion.[4] In were found to activate the amide in the alkynylation reaction.[12] addition, sila-Sonogashira reaction[5] provides an ideal protocol Subsequently different ligands were evaluated. Monodentate to convert silylated alkynes into internal alkynes.[6] phosphine ligand P(Cy) afforded the expected alkynylation However, in order to develop a successful catalytic amide to 3 product 3a in moderate yield (Table 1, entry 1). A slightly higher alkyne interconversion procedure, there are several challenges yield was obtained using the bidentate phosphine ligand dcype that need be to addressed: 1) the formation of alkyne [1,2-bis (dicyclohexyl phosphino)ethane] (Table 1, entry 2). The homocoupling products (Glaser-Hey coupling) has to be use of different bases such as Cs CO or CsF provided suppressed; 2) the use of strong bases which limits functional 2 3 unsatisfactory results (Table 1, entries 4, 5). Changing the group tolerance needs to be avoided; and 3) the undesired solvent to 1,4-dioxane resulted in an increased yield of 70% formation of ketons and tertiary alcohols through addition of (Table 1, entry 6). Changing the catalyst to ligand ratio resulted copper acetylide to the amide substrate has to be prevented in a considerably lower yield (Table 1, entry 8). A control (Scheme 1). experiment showed that no desired product was formed in the absence of the nickel catalyst and dcype ligand (Table 1, entries [a] M. Sc. W. Srimontree, M. Sc. A. Chatupheeraphat, Dr. H.-H. Liao, 9 and 10). Furthermore, the copper iodide is essential for Prof. Dr. M. Rueping achieving good yields of the desired product (Table 1, entry 11 Institute of Organic Chemistry vs 6). Notably, when the reaction was performed in the absence RWTH Aachen University Landoltweg 1, 52074 Aachen (Germany) of base, the desired product was obtained in an excellent yield E-mail: [email protected] of 99% (entry 12). In addition, performing the reaction with a lower catalyst loading resulted also in an excellent yield of 99% Supporting information for this article is given via a link at the end of the document. for the desired product (entry 13). COMMUNICATION Table 1: Optimization of the nickel catalyzed deamidative Csp2-Csp Table 2: The scope of nickel catalyzed Sonogashira cross-coupling with aryl coupling.[a] amides.[a,b] O O TIPS O O Ni(cod)2 TIPS N ligand, CuI Ni(cod) , dcype, CuI + N 2 Ar + Ar O TIPS base, solvent TIPS 1,4-dioxane, 150 °C 150 °C, 16 h O 16 h 1a 1 2a 3 2a 3a Entry Ligand Base Solvent Yield (%) TIPS TIPS 1 PCy3 K3PO4 toluene 60 3b, 53%[b] 3c, 87%[b] 2 dcype K3PO4 toluene 67 TIPS TIPS 3 dcypf K3PO4 toluene <5 4 dcype CsF toluene 16 3d, 99%[a] 3e, 86%[b] Me tBu 5 dcype Cs2CO3 toluene 0 TIPS TIPS 6 dcype K3PO4 dioxane 70 [b] [a] 7 dcype K3PO4 dioxane 73 3f, 92% [b] Ph MeO 3g, 48% [b,c] 8 dcype K3PO4 dioxane 44 [b,d] TIPS TIPS 9 dcype K3PO4 dioxane - MeO O b] 10[ - K3PO4 dioxane - [a] 3i, 72%[b] 3h, 91% O [e] 11 dcype K3PO4 dioxane 30 12[b] dcype - dioxane 99 TIPS TIPS 13[b,f] dcype - dioxane 99 3j, 98%[a] 3k, 78%[b] F F3C [a] Reaction conditions: 1a (0.2 mmol), 2a (0.6 mmol), Ni(cod)2 (10 mol%), dcype (40 mol%), CuI (10 mol%), base (2.0 equiv.), solvent (1 mL), 150 °C, 16 TIPS TIPS h, yield after isolation; [b] Using 2a (1.0 mmol); [c] Using dcype (20 mol%); [d] Without Ni(cod)2; [e] Without CuI; [f] Using Ni(cod)2 (5 mol%) and dcype (20 [b] [b] mol%). O 3l, 89% O 3m, 74% OMe With the optimized reaction conditions in hand, we further TIPS investigated the scope of this newly developed nickel catalyzed TIPS O Sonogashira cross-coupling reaction with a variety of amides 3n, 82%[b] 3o, 87%[b] and terminal alkynes. Initially, a number of different amide S substrates 1b-q bearing a broad range of substituents were studied and the results are summarized in Table 2. Regarding TIPS TIPS the application of phenyl derivatives, electron-neutral as well as S electron rich and poor phenyl derived amides 1c-l were 3p, 89%[b] 3q, 96%[a] alkynylated, providing products 3c-l with excellent yields. In N addition, substrates bearing methoxy, fluorine and methyl ester [a] Reaction conditions: 1 (0.2 mmol), 2a (1.0 mmol), Ni(cod)2 (5 mol%), dcype groups underwent reaction without affecting the substituents. (20 mol%), CuI (10 mol%) in dioxane (0.2 M) at 150 °C 16 h. [b] Using The latter observation is interesting as methoxy as well as Ni(cod)2 (20 mol%), dcype (40 mol%). Yields for isolated products. fluorine substituents have been reported as coupling partners in nickel catalyzed reactions. Furthermore, heterocyclic amides including furan, thiophen, benzofuran, benzothiophen and Trimethylsilyl and triethylsilyl alkynes 2b, c performed smoothly pyridine derivatives 1m-q are also tolerated under our reaction in the cross-coupling with 2-napthylamide 1a to provide the conditions and provided the products 3m-q in high yields. corresponding products 3r, s in 91% and 95% yield, respectively. We next examined the scope of the reaction with respect to The steric effect of the tertbutyldimethylsilyl group had a alkynes bearing different silyl groups (Table 3). detrimental impact on the rate of the reaction and the product 3t was obtained in moderate yield. To show the applicability of the method, the synthesis of conjugated enyne 3u starting form unsaturated amide 1u and alkyne 2a was attempted. Pleasingly, by applying our developed protocol, enyne 3u was obtained in 90% yield (Scheme 2). COMMUNICATION Table 3: The scope of nickel catalyzed cross-coupling of amides with terminal [a] silyl alkynes. TIPS O O R R N Cy P PCy O O SiR 2 2 O Ni(cod)2 3 reductive Ni oxidative N dcype, CuI elimination + addition SiR3 1,4-dioxane O 150 °C, 16 h 1a 2b-d 3 O Cy2 TIPS Cy2 P P Ni R Ni SiMe3 SiEt3 SiMe2(tBu) O P R P N Cy Cy2 C 2 O A 3r, 91% 3s, 95% 3t, 51% O Cy2 H TIPS CO P CuI [a] Reaction conditions: 1a (0.2 mmol), 2b-d (1.0 mmol), Ni(cod)2 (20 mol%), R Ni dcype (40 mol%), CuI (10 mol%) in dioxane (0.2 M) at 150 °C, 16 h, yields for decarbonylation P transmetalation Cy isolated products 3r-t.
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