Nickel-Catalyzed Suzuki-Miyaura Cross-Coupling Reaction of

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

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Nickel-Catalyzed Suzuki-Miyaura Cross-Coupling Reaction of Naphthyl and Quinolyl Alcohols with Boronic Acids Sunisa Akkarasamiyo, Jes̀ sica Margalef, and Joseph S. M. Samec* Department of Organic Chemistry, Stockholm University, 106 91 Stockholm, Sweden

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S Supporting Information *

ABSTRACT: A nickel-catalyzed C(sp3)−C(sp2) Suzuki cross-coupling of arylboronic acids and (hetero)naphthyl alcohols has been developed. A Ni(dppp)Cl2 complex showed the highest efficiency and broadest substrate scope. High functional group tolerance has been achieved where 35 compounds could be generated in good to excellent yields, including both primary and secondary benzylic alcohols. Mechanistic studies using multiple NMR techniques as well as ESI-HRMS showed that the C−O cleavage is facilitated by an activation of the benzylic alcohol through formation of a boronic ester intermediate.

T

increasing the E-factor of the overall reaction.11 Very few reports on Suzuki reactions of nonderivatized benzylic alcohols can be found in the literature. In 2015, Shi and co-workers pioneered the research field and reported a Pd(PPh3)4 catalyzed cross-coupling reaction with a broad scope of primary benzylic alcohols (Scheme 1a).12 In 2016, Roa and co-worker showed that Cu(OTf)2 can catalyze the Suzuki reaction of diarylmethanol to generate triarylmethanes in good yields (Scheme 1b).13 Shi’s group has also successfully performed nickel catalyzed cross-coupling reactions of benzylic alcohols using a reactive Grignard reagent as a nucleophilic partner to the alcohol (Scheme 1c).14 Nickel catalyzed Suzuki cross-coupling reactions of naphthyl and quinolyl alcohols have never been reported. Herein, we report the first nickel catalyzed Suzuki coupling reaction of both primary and secondary naphthyl and quinolyl alcohols and simple boronic acids to generate diarylmethanes (Scheme 1d). The importance of naphthyl and quinolyl structures in the pharmaceutical industry motivated us to develop this chemistry (Figure 1).15 6-Quinolinemethanol 1a and 3-fluorophenyl boronic acid 2a were chosen as coupling partners for the optimization of reaction conditions (Table 1). The enhanced reactivity and high atom-economy of boronic acids, prompted us to choose these substrates over other boronic reagents.16 In addition, they are cheap and a wide variety of them are commercially

he Suzuki reaction is one of the most reliable and widespread synthetic procedures to generate C(sp2)− 2 C(sp ) bonds in organic synthesis.1 In 2010, Suzuki was awarded the Nobel prize, together with Heck and Negishi, for their pioneering work on palladium-catalyzed cross-coupling reactions. Due to the usefulness of the methodology and also stability, low toxicity, and high functional group tolerance of organoboron compounds (in comparison to Grignard reagent), the methodology has been well adopted by both academia and industry.1 Coupling reactions are traditionally catalyzed by a palladium complex and performed between an organoboron compound and an aryl halide. Variations of the reaction have been developed such as utilizing other metals than palladium and also several electrophilic partners. Progressing the cross-coupling to more challenging benzylic electrophiles (C(sp3)) is of great interest. However, this chemistry is less established.2−4 Impressive stereospecific/ selective Suzuki reactions of derivatives of benzylic alcohol have been developed by the groups of Javo,5 Watson,6 Tredwell,7 and Shen.8 An alternative to organohalides would be the use of a nonderivatized alcohol as a coupling partner.9 If this would be possible, it would unlock a plethora of easily available compounds, including feedstocks from renewable sources. Due to the poor leaving group ability of the OH group and also the ability of the lone pair of the oxygen to coordinate to the metal and promoting a β-hydride elimination, this is a challenging task. Therefore, the alcohol is usually transformed into a derivative such as ether, ester, or tosylate before being subjected to the reaction.10 This adds a synthetic step usually with purification, thus lowering the atom economy and © XXXX American Chemical Society

Received: May 11, 2019

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DOI: 10.1021/acs.orglett.9b01669 Org. Lett. XXXX, XXX, XXX−XXX

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Organic Letters

Table 1. Screening for an Optimal Catalytic Systema

Scheme 1. C(sp3)−C(sp2) Cross-Coupling Reaction of Benzylic Alcohols

entry 1 2d 3 4 5 6 7 8 9 10 11 12 13 14 15 16e 17e

[Ni] cat.c Ni(dppp)Cl2 Ni(dppp)Cl2 Ni(dppp)Cl2 Ni(dppe)Cl2 Ni(dppe)(o-tol)Cl Ni(dppb)Cl2 Ni(dppf)Cl2 Ni(PPh)3Cl2 Ni(PCy)3Cl2 Ni(dppp)Cl2 Ni(dppp)Cl2 Ni(dppp)Cl2 Ni(dppp)Cl2 Ni(dppp)Cl2 Ni(dppp)Cl2 Ni(dppp)Cl2 Ni(cod)2

base

solvent

temp (°C)

product (%)b

K4P2O7 K4P2O7 K4P2O7 K4P2O7 K4P2O7

Toluene Toluene Toluene Toluene Toluene

100 100 80 100 100

98 78 9 93 94

K4P2O7 K4P2O7 K4P2O7 K4P2O7 K4P2O7 K4P2O7 K4P2O7 K3PO4 K2HPO4 − K4P2O7 K4P2O7

Toluene Toluene Toluene Toluene MeCN THF TAA Toluene Toluene Toluene Toluene Toluene

100 100 100 100 100 100 100 100 100 100 100 100

95 98 95 88 10 35 93 70 0 0 29 0

a

6-Quinolinemethanol 1a (0.2 mmol), 3-fluorophenylboronic acid 2a (0.6 mmol), base (0.6 mmol), [Ni](10 mol %), toluene (1 mL), 80 °C for 8 h and then 100 °C for 17 h. bNMR yield using 1,3,5trimethoxybenzene as an internal standard. cdppe: 1,2-bis(diphenylphosphino)ethane. dppp: 1,3-bis(diphenylphosphino)propane. dppb: 1,4-Bis(diphenylphosphino)butane. dppf : 1,1'-bis(diphenylphosphino)ferrocene. TAA : tert-amyl alcohol. dThe reaction was heated to 100 °C for 17 h (without prerunning at 80 °C for 8 h). e dppp (12 mol %) was added. Figure 1. Examples of biologically active diarylmethane compounds.

entries 1, 10−12). The reaction required the addition of a base (Table 1, entry 15). No cross-coupling product 3aa was observed when the reaction was performed without addition of base. K4P2O7 provided the best catalytic performance (Table 1, entries 1, 13−14). A decrease in the reactivity was observed when using an excess of phosphine ligand (Table 1, entry 16). Using Ni(0) as a catalyst precursor gave no reactivity in the present system (Table 1, entry 17). Having the optimal conditions in hand, the scope of arylboronic acids and benzylic alcohols was explored considering these functional groups (Scheme 2). There are numerous functional groups sensitive to nickel catalysis. For instance, C−F,17 C−OMe,18 C−SMe,19 and C−COR20 bonds have been reported to undergo cleavage by nickel complexes. Gratifyingly, none of the mentioned bonds were cleaved using the optimized reaction conditions (Scheme 2, compounds 3aa−3ag, 3aj−3al, and 3an). Thus, a wide range of diarylmethane compounds were obtained in good to excellent yields. A wide range of boronic acids containing both electron-donating (2j−2o) and electronwithdrawing groups (2a−2g) were employed, and the corresponding products were obtained in good to excellent yields. However, we observed that strongly electron-deficient boronic acids, such as 2d−2g, required a higher reaction temperature to achieve high yields (125 °C). 3-Quinolinemethanol 1b and 5-quinolinemethanol 1c also performed well to give products 3ba and 3ca in 90% yield. We were pleased to see that we could expand the scope of alcohols to the naphthalene systems 1d−1g. Hence, diarylmethane product

available. Serendipitously, we found that stirring the reaction at 80 °C for 8 h and then at 100 °C, overnight gave the desired product in an excellent yield (Table 1, entry 1). If the reaction was heated to 100 °C from start, lower yield of the desired product was obtained, where competing reactivities including: homocoupling of the boronic acid (∼7−23% isolated yield), homocoupling of the alcohols (4−14% isolated yield), protodeboronation, and also reduction of the alcohols were observed, vide inf ra (Table 1, entry 2). If the temperature was not increased to 100 °C, we observed low conversion toward the desired diarylmethane product (Table 1, entry 3). Details about these observations will be discussed later. Next, commercially available nickel-phosphine complexes were screened. We found that the bite angle did not play an important role in the reactivity, since 93−98% yield of diarylmethane was observed in all cases (Table 1, entries 1, 4−8). The highest yields were obtained with a Ni-complex with 1,3-bis(diphenylphosphino)propane (dppp) and 1,1′bis(diphenylphosphino)ferrocene (dppf) as ligands. However, the dppp ligand showed a broader substrate scope and was thus chosen for this study (vide infra, Supporting Information (SI) section 3). Electron-rich tricyclohexylphosphine provided a lower yield than aromatic phosphines (Table 1, entry 9 vs 1, 4−8). Using Ni(dppp)Cl2 as a catalyst precursor, we studied other reaction parameters. Yields of desired product were lower with more coordinating solvents; hence, toluene was found to be the best solvent for this transformation (Table 1, B

DOI: 10.1021/acs.orglett.9b01669 Org. Lett. XXXX, XXX, XXX−XXX

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(66−94%) (Scheme 3). When alcohol 1a and arylboronic acid 2a (3 equiv) were mixed in toluene at 80 °C for 18 h (Scheme Scheme 3. Nickel Catalyzed C(sp3)−C(sp2) Suzuki CrossCoupling of Secondary Alcoholsa

a Benzylic alcohol (0.2 mmol), ArB(OH)2 (0.6 mmol), K4P2O7 (0.6 mmol), Ni(dppp)Cl2 (10 mol %), toluene (1 mL), 80 °C for 8 h then 125 °C for 17 h. NMR yield using 1,3,5-trimethoxybenzene as an internal standard.

4A), boronic esters 6−8 were identified by 1H, 11B, and 19F NMR and HRMS analysis (SI, Figures 4−7). This shows that the boronic esters are formed and may play a role in activating the alcohol in the reaction. To further support this proposal, additional experiments were performed. First, we generated boronic ester 6 by mixing boronic acid 2a and quinolyl alcohol 1a at 80 °C overnight, followed by adding another boronic acid (2k) together with a Ni-catalyst and base and increasing the temperature. This gave a ratio of products 3aa/3ak of 2:1 (Scheme 4B). This supports our proposal. This is in contrast to the proposed activation in the palladium-catalyzed crosscoupling reported by Shi and co-workers, where the boroxine operates as a Lewis acid.12 We also performed the opposite reaction, generating the ester of 2k and 1a at 80 °C, and then added 2a together with a nickel catalyst and base. This gave a ratio of products 3aa:3ak of 3:1 (Scheme 4C). Finally, a control reaction was performed where 2a and 2k were mixed with 1a together with the Nicatalyst and base initially at 80 °C and then at 100 °C giving a ratio of products 3aa:3ak of 3:1 (Scheme 4D). These experiments clearly demonstrate that the formation of a boronic ester intermediate is crucial for C−O bond cleavage of benzylic alcohol Thus, at 80 °C a boronic ester is formed between boronic acid and naphthyl/quinolyl alcohol, which enables the C−O cleavage. For instance, the use of phenyl boroxine gave a lower yield of the desired product than when using boronic acid, whereas no reaction was observed when phenylboronic pinacal ester was used (SI, Table 1). The reaction mechanism was further examined by studying the reaction mixture by ESI-HRMS. We mixed 1a, 2a, catalyst, and base at 80 °C overnight and then increased the temperature to 100 °C for 1 h, before taking a sample and injecting it to the mass detector. Interestingly, we identified several complexes and intermediates as well as the product (Figure 2). Ni(dppp)(OH) (D) was observed as a minor peak in the spectrum with an m/z of 487 au. A large peak for Ni(dppp)(C6H4F) (E) was observed with a mass of m/z of 565 au. Also, Ni(dppp)(C6H4F)(C10H8N)− (OH) (G) was observed with a mass of m/z 724 au. In addition to these metal complexes, product 3aa and boronic ester were observed in the

a Benzylic alcohol (0.2 mmol), ArB(OH)2 (0.6 mmol), K4P2O7 (0.6 mmol), Ni(dppp)Cl2 (10 mol %), toluene (1 mL), 80 °C for 8 h and then 100 °C for 17 h; NMR yield using 1,3,5-trimethoxybenzene as an internal standard. bIsolated yield. cReactions performed at 80 °C for 8 h and then at 125 °C for 17 h.

3da, 3e(a,h,p), 3f(a,h,p), and 3g(a,h) were obtained in good to excellent yields (55−98%). Benzothiophenemethanol 1h− 1i could be also used to provide compounds 3ha and 3ia in 76% and 50% yields, respectively. For these substrates a higher reaction temperature (125 °C) was required in order to obtain high yields. To the best of our knowledge, Suzuki reaction of secondary benzylic alcohols has only been reported for highly reactive diarylmethanols.13 Secondary benzylic alcohols with an αmethyl group are challenging substrates because a β-hydride elimination could occur as a side reaction. Gratifyingly, we could achieve diarylmethanes 5 from challenging substrates 4 and arylboronic acids 2a and 2p in good to excellent yields C

DOI: 10.1021/acs.orglett.9b01669 Org. Lett. XXXX, XXX, XXX−XXX

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Organic Letters Scheme 4. Control Experiments Using Quinoline Derivative 1a and Boronic Acids 2a and 2k

Scheme 5. Proposed Reaction Mechanism

Figure 2. ESI-HRMS of reaction of 1a and 2a.

mass spectrum. Based on the experimental data, we propose the following reaction mechanism (Scheme 5). Boronic esters are formed at 80 °C; however, the redox chemistry is very slow at this temperature. If the reaction is performed without preheating, the redox chemistry starts in the absence of boronic esters resulting in homocouplings and disproportionations/reductions. The catalyst precursor, Ni(dppp)Cl2 A, is activated by 2 equiv of arylboronic acid and base to generate Ni(dppp)(OH) D, which proceeds through formation of catalytic amounts of diaryl coupling product, which is always observed as a minor byproduct in the reaction mixture. Transmetalation of D with arylboronic acid generates complex E, which was also detected by ESI-HRMS. Next, intermediate E undergoes oxidative addition of the preformed boronic ester to give complex F. The reductive elimination is then promoted

by attack of a hydroxide ion generated from K4P2O7 and water, via detected intermediate G, leading to the desired coupling product and regeneration of Ni(dppp)(OH) D. Thus, boronic D

DOI: 10.1021/acs.orglett.9b01669 Org. Lett. XXXX, XXX, XXX−XXX

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Reactions. ACS Catal. 2017, 7 (2), 1108−1112. (c) Wang, T.; Yang, S.; Xu, S.; Han, C.; Guo, G.; Zhao, J. Palladium Catalyzed Suzuki Cross-Coupling of Benzyltrimethylammonium Salts via C−N Bond Cleavage. RSC Adv. 2017, 7, 15805−15808. (d) Singh, M. K.; Lakshman, M. K. Diarylmethanes through an Unprecedented Palladium-Catalyzed C-C Cross-Coupling of 1-(Aryl)methoxy1HBenzotriazoles with Arylboronic Acids. ChemCatChem 2015, 7, 4156−4162. (e) Zhang, Y.; Feng, M.-T.; Lu, J.-M. N-Heterocyclic Carbene−Palladium(II)−1-Methylimidazole Complex Catalyzed Suzuki−Miyaura Coupling of Benzylic Chlorides with Arylboronic Acids or Potassium Phenyltrifluoroborate in Neat Water. Org. Biomol. Chem. 2013, 11, 2266−2272. (f) Ohsumi, M.; Nishiwaki, N. Selective Synthesis of (Benzyl)biphenyls by Successive Suzuki−Miyaura Coupling of Phenylboronic Acids with 4BromobenzylAcetate under Air Atmosphere. ACS Omega 2017, 2, 7767−7771. (3) (a) Wu, K.; Doyle, A. G. Parameterization of Phosphine Ligands Demonstrates Enhancement of Nickel Catalysis via Remote Steric Effects. Nat. Chem. 2017, 9, 779−784. (b) Tobisu, M.; Yasutome, A.; Kinuta, H.; Nakamura, K.; Chatani, N. 1,3-Dicyclohexylimidazol-2ylidene as a Superior Ligand for the Nickel-Catalyzed CrossCouplings of Aryl and Benzyl Methyl Ethers with Organoboron Reagents. Org. Lett. 2014, 16, 5572−5575. (c) Liao, J.; Guan, W.; Boscoe, B. P.; Tucker, J. W.; Tomlin, J. W.; Garnsey, M. R.; Watson, M. P. Transforming Benzylic Amines into Diarylmethanes: CrossCouplings of Benzylic Pyridinium Salts via C−N Bond Activation. Org. Lett. 2018, 20, 3030−3033. (d) Chen, Q.; Fan, X.-H.; Zhang, L.P.; Yang, L.-M. Ni(II) Source as a Pre-Catalyst for the CrossCoupling of Benzylic Pivalates with Arylboronic Acids: Facile Access to Tri- and Diarylmethanes. RSC Adv. 2015, 5, 15338−15340. (e) Ariki, Z. T.; Maekawa, Y.; Nambo, M.; Crudden, C. M. Preparation of Quaternary Centers via Nickel-Catalyzed Suzuki− Miyaura Cross-Coupling of Tertiary Sulfones. J. Am. Chem. Soc. 2018, 140, 78−81. (4) (a) Sun, Y.-Y.; Yi, J.; Lu, X.; Zhang, Z.-Q.; Xiao, B.; Fu, Y. CuCatalyzed Suzuki−Miyaura Reactions of Primary and Secondary Benzyl Halides with Arylboronates. Chem. Commun. 2014, 50, 11060−11062. (b) Procter, R. J.; Dunsford, J. J.; Rushworth, P. J.; Hulcoop, D. G.; Layfield, R. A.; Ingleson, M. J. A Zinc Catalyzed C(sp3)-C(sp2) Suzuki−Miyaura Cross-Coupling Reaction Mediated by Aryl-Zincates. Chem. - Eur. J. 2017, 23, 15889−15893. (c) Bedford, R. B.; Hall, M. A.; Hodges, G. R.; Huwe, M.; Wilkinson, M. C. Simple Mixed Fe−Zn Catalysts for the Suzuki Couplings of Tetraarylborates with Benzyl Halides and 2-Halopyridines. Chem. Commun. 2009, 6430−6432. (d) Bedford, R. B.; Brenner, P. B.; Carter, E.; Carvell, T. W.; Cogswell, P. M.; Gallagher, T.; Harvey, J. N.; Murphy, D. M.; Neeve, E. C.; Nunn, J.; Pye, D. R. Expedient Iron-Catalyzed Coupling of Alkyl, Benzyl and Allyl Halides with Arylboronic Esters. Chem. Eur. J. 2014, 20, 7935−7938. (e) Bedford, R. B.; Gallagher, T.; Pye, D. R.; Savage, W. Towards Iron-Catalysed Suzuki Biaryl CrossCoupling: Unusual Reactivity of 2-Halobenzyl Halides. Synthesis 2015, 47, 1761−1765. (5) (a) Tollefson, E. J.; Hanna, L. E.; Jarvo, E. R. Stereospecific Nickel-Catalyzed Cross-Coupling Reactions of Benzylic Ethers and Esters. Acc. Chem. Res. 2015, 48 (8), 2344−2353. (b) Johnson, A. G.; Tranquilli, M. M.; Harris, M. R.; Jarvo, E. R. Selective Synthesis of Either Enantiomer of an Anti-Breast Cancer Agent via a Common Enantioenriched Intermediate. Tetrahedron Lett. 2015, 56 (23), 3486−3488. (c) Harris, M. R.; Hanna, L. E.; Greene, M. A.; Moore, C. E.; Jarvo, E. R. Retention or Inversion in Stereospecific Nickel-Catalyzed Cross-Coupling of Benzylic Carbamates with Arylboronic Esters: Control of Absolute Stereochemistry with an Achiral Catalyst. J. Am. Chem. Soc. 2013, 135 (9), 3303−3306. (6) (a) Zhou, Q.; Srinivas, H. D.; Dasgupta, S.; Watson, M. P. Nickel-Catalyzed Cross-Couplings of Benzylic Pivalates with Arylboroxines: Stereospecific Formation of Diarylalkanes and Triarylmethanes. J. Am. Chem. Soc. 2013, 135 (9), 3307−3310. (b) Zhou, Q.; Cobb, K. M.; Tan, T.; Watson, M. P. Stereospecific Cross Couplings To Set Benzylic, All-Carbon Quaternary Stereocenters in High Enantiopurity. J. Am. Chem. Soc. 2016, 138 (37), 12057−12060.

acid has three roles: (i) activation of catalyst precursor; (ii) activation of alcohol; and (iii) as a coupling partner. A simple and robust nickel (I/III)-catalyzed C(sp3)−C(sp2) Suzuki cross-coupling of π-extended primary and secondary benzylic alcohols to generate diarylmethanes has been developed. The products were in most cases obtained in good to excellent yields. This atom-efficient Suzuki crosscoupling has a broad substrate scope in respect to quinolyl and naphthyl alcohols and also boronic acids. In addition, although a Ni-catalyst is used, the reaction is easy to perform without requirement of glovebox conditions. Mechanistic studies support that the C−O bond of the alcohol is activated via formation of arylboronate esters which is then cleaved via Ni(I) aryl species. Thus, the aryl boronic acid has several roles: not only as both a coupling partner and an activating agent for the alcohols but also to initiate the catalyst.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.orglett.9b01669. Experimental procedures and spectral data (PDF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Joseph S. M. Samec: 0000-0001-8735-5397 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS Formas and Stiftelsen Olle Engkvists Byggmästare. REFERENCES

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DOI: 10.1021/acs.orglett.9b01669 Org. Lett. XXXX, XXX, XXX−XXX