Decarbonylative Methylation of Aromatic Esters by a Nickel Catalyst

Letter Cite This: Org. Lett. XXXX, XXX, XXX−XXX

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Decarbonylative Methylation of Aromatic Esters by a Nickel Catalyst Toshimasa Okita, Kei Muto, and Junichiro Yamaguchi* Department of Applied Chemistry, Waseda University, 3-4-1 Ohkubo, Shinjuku, Tokyo 169-8555, Japan S Supporting Information *

ABSTRACT: A Ni-catalyzed decarbonylative methylation of aromatic esters was achieved using methylaluminums as methylating agents. Dimethylaluminum chlorides uniquely worked as the methyl source. Because of the Lewis acidity of aluminum reagents, less reactive alkyl esters could also undergo the present methylation. By controlling the Lewis acidity of aluminum reagents, a chemoselective decarbonylative cross-coupling between alkyl esters and phenyl esters was successful.

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evelopment of a novel and efficient C−C bond-forming reaction is a topic of utmost importance in the field of organic chemistry. Transition-metal-catalyzed cross-coupling between haloarenes and organic metals has been regarded as one of the most useful and reliable synthetic methods and has been utilized for the synthesis of various functional organic molecules ranging from pharmaceuticals to organic electronic devices.1 Recently, several advanced methods using unconventional aryl electrophiles such as phenols,2 anilines,3 and thiophenols4 have emerged. The utilization of these alternatives to haloarenes is beneficial because it opens a new synthetic strategy and it allows chemists to exploit other inexpensive sources of chemical feedstock. In this context, our continuous interest has been aimed at the development of coupling reactions using arenecarboxylate derivatives such as aromatic esters as unconventional aryl electrophiles (Figure 1A).5−8 Successful examples have been the development of decarbonylative C−C couplings such as arylation6a−d and alkynylation.6e However, a decarbonylative coupling involving alkyl nucleophiles has remained a challenge. Owing to the low reactivity of alkyl nucleophiles toward transition metal catalysts and the involvement of several undesired pathways such as β-H elimination in a catalytic cycle,9 the utilization of alkylmetal species for the decarbonylative cross-coupling of esters is still a challenging transformation. In 2017, Rueping’s group reported the decarbonylative coupling of aromatic esters with alkylzincs by a nickel/ dcype catalyst (dcype: 1,2-bis(dicyclohexylphosphino)ethane) (Figure 1B).10a Later, the same group extended this chemistry for the reaction using alkylborons.10b These are successful examples of decarbonylative alkylation; however, only aromatic phenyl esters are applicable substrates. Herein, we report that the use of dimethylaluminum chlorides realizes the decarbonylative methylation of aromatic esters.11 Harnessing the dual role of aluminum chlorides as methyl nucleophiles and Lewis acids, we also succeeded in using simple aromatic alkyl esters in this reaction. We began this investigation to find applicable methylaluminums12 with phenyl 1-naphthoate (1A) under our in-house catalyst, Ni(OAc)2/dcypt,13 as the initial reaction conditions © XXXX American Chemical Society

Figure 1. (A) Decarbonylative C−C bond formations of aromatic esters. (B) Decarbonylative alkylation of aromatic esters.

(Scheme 1). To our surprise, among various methylaluminums, dimethylaluminum chloride (2a) gave the best result, giving the corresponding methylated product in 64% yield. Other aluminum reagents such as trimethylaluminum and methylaluminum dichloride were found to be less effective for this transformation. Encouraged by this initial discovery, we subjected another aromatic ester 1B to react with 2a in the presence of Ni/dcypt (Table 1, entry 1).14 However, the reaction yield was not satisfactory (32%); thus, we set out to investigate more general conditions. Ethylene-bridged diphosphines furnished 3Ba, albeit in poor yields (Table 1, entries 2 and 3). Gratifyingly, Received: April 18, 2018

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DOI: 10.1021/acs.orglett.8b01233 Org. Lett. XXXX, XXX, XXX−XXX

Letter

Organic Letters Scheme 2. Substrate Scope Using Phenyl Esters 1a

Scheme 1. Investigation of Applicable Methylaluminums

Table 1. Screening of Reaction Conditionsa

entry

Ni

ligand

3Ba, GC yield (%)b

1 2 3 4 5 6 7 8 9 10

Ni(acac)2 Ni(acac)2 Ni(acac)2 Ni(acac)2 Ni(acac)2 Ni(acac)2 Ni(acac)2 Ni(OAc)2 Pd(acac)2 none

dcypt dcype dppe dppp PCy3·HBF4c ICy·HBF4c none dppp dppp dppp

32 13 29 53 9 2 trace 52 33 0

a Conditions: 1B (0.20 mmol), 2a (hexane solution, 1.5 equiv), Ni salt (5 mol %), ligand (10−20 mol %), 1,4-dioxane (0.50 mL), 150 °C, 16 h. bGC yield was determined by using n-decane as an internal standard. cLigand (20 mol %) and NaOt-Bu (20 mol %) were used.

a

Conditions: (A) Ni(acac)2 (10 mol %), dppp (20 mol %), 1 (0.40 mmol), 2 (hexane solution, 1.5 equiv), 1,4-dioxane (1.0 mL), 170 °C, 16 h. (B) Ni(acac)2 (5 mol %), dcypt (10 mol %), 1 (0.40 mmol), 2 (hexane solution, 1.5 equiv), 1,4-dioxane (1.0 mL), 170 °C, 16 h. bGC yield. cNi(OAc)2 (10 mol %) and LiCl (1.5 equiv) were used. dNMR yield. e0.20 mmol scale. fdppp (10 mol %) and LiCl (1.5 equiv) were used.

it was found that an inexpensive and simple diphosphine, dppp, gave a better yield (Table 1, entry 4). The use of electron-rich monodentate ligands such as PCy3 as well as an NHC ligand decreased the reaction yield (Table 1, entries 5 and 6). A methylated arene product was not obtained when the ligand was omitted (Table 1, entry 7). This reaction allowed the use of Ni(OAc)2 to produce 3Ba in almost the same yield as the Ni(acac)2 conditions. It is noteworthy that palladium is also an effective metal, although the reaction efficiency was inferior to nickel (Table 1, entry 9). This reaction did not proceed in the absence of transition metals (Table 1, entry 10). Throughout this screening process, we did not detect any nondecarbonylative products, such as methyl ketones. Using the optimized conditions, the substrate scope of this reaction was investigated (Scheme 2). The reaction yields of several compounds were determined by GC or NMR analysis due to the high volatility of the products. π-Extended aromatic systems such as naphthalenes as well as anthracenes showed good reactivity to generate the corresponding methylated arenes. Benzoate derivatives could also undergo the present methylation. This catalytic system was not influenced by steric hindrance (e.g., 1G), giving the corresponding ortho-substituted methyl arene. Benzoates bearing electron-donating substituents were also methylated. Highly polar substituents such as

sulfonamide (1I) were compatible under the catalytic conditions. This methylation protocol was also applicable to heteroaromatic esters. The methylation of aromatic esters containing five-membered heteroaromatics, such as benzothiophene (1L), indole (1M), and thiazole (1N), was successful. Electrondeficient azines (1O) could be methylated. Regarding the applicable other alkyl nucleophiles, diethylaluminum chloride (2b) was also reactive, although 2b potentially undergoes β-H elimination as an undesired pathway. Based on the hypothesis that the Lewis acidity of methylaluminums would enhance the electrophilicity of the ester moiety, we modified the ester starting material from phenyl esters to alkyl esters (Scheme 3).7h,15 Delightfully, slightly modified reaction conditions using a Ni(OTs)2/dcypt catalyst worked well for the alkylation of aromatic methyl esters (4A), delivering the corresponding methylated arenes. B

DOI: 10.1021/acs.orglett.8b01233 Org. Lett. XXXX, XXX, XXX−XXX

Letter

Organic Letters Scheme 3. Substrate Scope of Aromatic Methyl Esters 4a

In summary, we have developed a decarbonylative methylation of aromatic esters by a nickel catalyst. Dimethylaluminum chlorides work not only as alkylating agents but also as Lewis acids in this reaction, realizing the methylation of otherwise unreactive aromatic alkyl esters. Further studies of the Lewis acid effect for other decarbonylative transformations are ongoing in our group.

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ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.orglett.8b01233. Detailed experimental procedures, spectral data for all compounds, and 1H and 13C NMR spectra (PDF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Conditions: Ni(OTs)2 (5 mol %), dcypt (10 mol %), 4 (0.40 mmol), 2a (hexane solution, 1.5 equiv), 1,4-dioxane (1.0 mL), 170 °C, 16 h. b GC yield. c1H NMR yield.

ORCID

Similarly, ethyl (5A) and n-Bu ester (6A) showed good reactivity; however, sterically bulky esters such as isopropyl (7A) resulted in a poor yield. With this result, we further investigated the scope of aromatic methyl esters. Generally, we found that most aromatic alkyl esters showed similar reactivity to the corresponding phenyl esters to afford methyl arenes 3. Naphthoates (4A, 4C, 4P, and 4Q) and benzoates (4B and 4G) could be methylated in good yields. Sterically hindered 4G also underwent a reaction to give 3Ga. Heteroaromatic esters (4L and 4M) could be methylated. Although recent computational work done by Uchiyama and Wang documented that an electron-rich nickel catalyst can accelerate the ether C−O bond scission with the support of a Lewis acid,16 the methoxy group was completely tolerated under these reaction conditions. Next, we wanted to investigate whether this reaction is applicable to the chemoselective functionalization of alkyl versus phenyl esters using methyl phenyl naphthalenedicarboxylate 8 (Scheme 4A). It is envisaged that the

Notes

a

Kei Muto: 0000-0001-8301-4384 Junichiro Yamaguchi: 0000-0002-3896-5882 The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by JSPS KAKENHI Grant Number JP18H04272, JP16H04148 (to J.Y.), JP17K14453, and JP18H04661 (to K.M.). The Materials Characterization Central Laboratory in Waseda University is acknowledged for HRMS measurement.

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REFERENCES

(1) Metal-catalyzed cross-coupling reactions and more; de Meijere, A., Bräse, S., Oestreich, M., Eds.; Wiley-VCH: Weinheim, 2014. (2) For reviews, see: (a) Rosen, B. M.; Quasdorf, K. W.; Wilson, D. A.; Zhang, N.; Resmerita, A.-M.; Garg, N. K.; Percec, V. Chem. Rev. 2011, 111, 1346. (b) Tobisu, M.; Chatani, N. Top. Curr. Chem. 2016, 41, 374. (3) For aniline-based electrophiles in alkylative couplings, see: (a) Roglans, A.; Pla-Quintana, A.; Moreno-Mañas, M. Chem. Rev. 2006, 106, 4622. (b) Blakey, S. B.; MacMillan, D. W. C. J. Am. Chem. Soc. 2003, 125, 6046. (4) For thiophenol-based electrophiles in alkylative couplings, see: (a) Modha, S. G.; Mehta, V. P.; Van der Eycken, E. V. Chem. Soc. Rev. 2013, 42, 5042. (b) Pan, F.; Shi, Z.-J. ACS Catal. 2014, 4, 280. (5) For a review, see: Takise, R.; Muto, K.; Yamaguchi, J. Chem. Soc. Rev. 2017, 46, 5864. (6) For our contributions in the development of decarbonylative coupling, see: (a) Amaike, K.; Muto, K.; Yamaguchi, J.; Itami, K. J. Am. Chem. Soc. 2012, 134, 13573. (b) Muto, K.; Yamaguchi, J.; Musaev, D. G.; Itami, K. Nat. Commun. 2015, 6, 7508. (c) Amaike, K.; Itami, K.; Yamaguchi, J. Chem. - Eur. J. 2016, 22, 4384. (d) Muto, K.; Hatakeyama, T.; Itami, K.; Yamaguchi, J. Org. Lett. 2016, 18, 5106. (e) Okita, T.; Kumazawa, K.; Takise, R.; Muto, K.; Itami, K.; Yamaguchi, J. Chem. Lett. 2017, 46, 218. (f) Takise, R.; Isshiki, R.; Muto, K.; Itami, K.; Yamaguchi, J. J. Am. Chem. Soc. 2017, 139, 3340. (g) Isshiki, R.; Takise, R.; Itami, K.; Muto, K.; Yamaguchi, J. Synlett 2017, 28, 2599. (h) Isshiki, R.; Muto, K.; Yamaguchi, J. Org. Lett. 2018, 20, 1150. (i) Ishitobi, K.; Isshiki, R.; Asahara, K. K.; Lim, C.; Muto, K.; Yamaguchi, J. Chem. Lett. 2018, DOI: 10.1246/cl.180226. (7) For representative examples of decarbonylative coupling of aromatic esters, see: (a) Gooßen, L. J.; Paetzold, J. Angew. Chem., Int.

Scheme 4. Chemoselective Alkyl Couplings of 8

suppression of Lewis acidity of the aluminum reagent would circumvent the bond scission of the methyl ester moiety. Thus, we performed the reaction of 8 in the presence of a tertiary amine, which acts as a poisoning reagent of the Lewis acid. Pleasingly, we succeeded in methylating only at the phenyl ester moiety, obtaining product 10 in moderate yield. It is worth noting that when the tertiary amine was not used, we observed the dimethylated product 9 as the major product. C

DOI: 10.1021/acs.orglett.8b01233 Org. Lett. XXXX, XXX, XXX−XXX

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Organic Letters Ed. 2002, 41, 1237. (b) Gooßen, L. J.; Paetzold, J. Angew. Chem., Int. Ed. 2004, 43, 1095. (c) LaBerge, N. A.; Love, J. A. Eur. J. Org. Chem. 2015, 2015, 5546. (d) Guo, L.; Chatupheeraphat, A.; Rueping, M. Angew. Chem., Int. Ed. 2016, 55, 11810. (e) Pu, X.; Hu, J.; Zhao, Y.; Shi, Z. ACS Catal. 2016, 6, 6692. (f) Yue, H.; Guo, L.; Liao, H.-H.; Cai, Y.; Zhu, C.; Rueping, M. Angew. Chem., Int. Ed. 2017, 56, 4282. For related nondecarbonylative couplings of aromatic esters, see: (g) Tatamidani, H.; Kakiuchi, F.; Chatani, N. Org. Lett. 2004, 6, 3597. (h) Hie, L.; Fine Nathel, N. F.; Hong, X.; Yang, Y.-F.; Houk, K. N.; Garg, N. K. Angew. Chem., Int. Ed. 2016, 55, 2810. (i) Ben Halima, T.; Zhang, W.; Yalaoui, I.; Hong, X.; Yang, Y.-F.; Houk, K. N.; Newman, S. G. J. Am. Chem. Soc. 2017, 139, 1311. (8) For related transformation using aromatic amides, see: (a) Meng, G.; Shi, S.; Szostak, M. Synlett 2016, 27, 2530. (b) Kajita, Y.; Matsubara, S.; Kurahashi, T. J. Am. Chem. Soc. 2008, 130, 6058. (c) Meng, G.; Szostak, M. Angew. Chem., Int. Ed. 2015, 54, 14518. (d) Shi, S.; Meng, G.; Szostak, M. Angew. Chem., Int. Ed. 2016, 55, 6959. (e) Hu, J.; Zhao, Y.; Liu, J.; Zhang, Y.; Shi, Z. Angew. Chem., Int. Ed. 2016, 55, 8718. (f) Liu, X.; Yue, H.; Jia, J.; Guo, L.; Rueping, M. Chem. - Eur. J. 2017, 23, 11771. (g) Liu, C.; Szostak, M. Angew. Chem., Int. Ed. 2017, 57, 3939. (h) Srimontree, W.; Chatupheeraphat, A.; Liao, H. H.; Rueping, M. Org. Lett. 2017, 19, 3091. For related nondecarbonylative couplings of aromatic amides, see: (i) Hie, L.; Fine Nathel, N. F.; Shah, T. K.; Baker, E. L.; Hong, X.; Yang, Y.-F.; Liu, P.; Houk, K. N.; Garg, N. K. Nature 2015, 524, 79. (j) Weires, N. A.; Baker, E. L.; Garg, N. K. Nat. Chem. 2016, 8, 75. (k) Dander, J. E.; Garg, N. K. ACS Catal. 2017, 7, 1413. (9) Jana, R.; Pathak, T. P.; Sigman, M. S. Chem. Rev. 2011, 111, 1417. (10) (a) Liu, X.; Jia, J.; Rueping, M. ACS Catal. 2017, 7, 4491. (b) Chatupheeraphat, A.; Liao, H. H.; Srimontree, W.; Guo, L.; Minenkov, Y.; Poater, A.; Cavallo, L.; Rueping, M. J. Am. Chem. Soc. 2018, 140, 3724. (11) The reviews documenting the importance of methylation in medicinal chemistry, see: (a) Schönherr, H.; Cernak, T. Angew. Chem., Int. Ed. 2013, 52, 12256. (b) Barreiro, E. J.; Kümmerle, A. E.; Fraga, C. A. M. Chem. Rev. 2011, 111, 5215. (12) The representative coupling reactions using methylaluminums, see: (a) Morioka, T.; Nishizawa, A.; Nakamura, K.; Tobisu, M.; Chatani, N. Chem. Lett. 2015, 44, 1729. (b) Shang, R.; Ilies, L.; Nakamura, E. J. Am. Chem. Soc. 2015, 137, 7660. (13) (a) Takise, R.; Muto, K.; Yamaguchi, J.; Itami, K. Angew. Chem., Int. Ed. 2014, 53, 6791. (b) Koch, E.; Takise, R.; Studer, A.; Yamaguchi, J.; Itami, K. Chem. Commun. 2015, 51, 855. (14) For details, see the Supporting Information. (15) (a) Yue, H.; Zhu, C.; Rueping, M. Org. Lett. 2018, 20, 385. (b) Liu, X.; Hsiao, C.-C.; Kalvet, I.; Leiendecker, M.; Guo, L.; Schoenebeck, F.; Rueping, M. Angew. Chem., Int. Ed. 2016, 55, 6093. (16) Ogawa, H.; Minami, H.; Ozaki, T.; Komagawa, S.; Wang, C.; Uchiyama, M. Chem. - Eur. J. 2015, 21, 13904.

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DOI: 10.1021/acs.orglett.8b01233 Org. Lett. XXXX, XXX, XXX−XXX