Cobalt-catalyzed oxidative annulation of aromatic tertiary amines with electron-deficient maleimides leading to tetrahydroquinoline derivatives

Cobalt-catalyzed oxidative annulation of aromatic tertiary amines with electron-deficient maleimides leading to tetrahydroquinoline derivatives

Tetrahedron Letters 57 (2016) 5449–5452 Contents lists available at ScienceDirect Tetrahedron Letters journal homepage: www.elsevier.com/locate/tetl...

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Tetrahedron Letters 57 (2016) 5449–5452

Contents lists available at ScienceDirect

Tetrahedron Letters journal homepage: www.elsevier.com/locate/tetlet

Cobalt-catalyzed oxidative annulation of aromatic tertiary amines with electron-deficient maleimides leading to tetrahydroquinoline derivatives Norio Sakai ⇑, Shun Matsumoto, Yohei Ogiwara Department of Pure and Applied Chemistry, Faculty of Science and Technology, Tokyo University of Science (RIKADAI), Noda, Chiba 278-8510, Japan

a r t i c l e

i n f o

Article history: Received 8 September 2016 Revised 17 October 2016 Accepted 20 October 2016 Available online 21 October 2016

a b s t r a c t Described herein is a CoCl2–TBHP (t-butyl hydroperoxide) system that efficiently catalyzes the oxidative annulation of aromatic tertiary amines with a typical electron-deficient alkene, N-substituted maleimides, producing the corresponding polycyclic tetrahydroquinoline derivatives. This oxidizing system could also be applied to the annulation of an electron-rich alkene. Ó 2016 Elsevier Ltd. All rights reserved.

Keywords: Cobalt Oxidation Annulation Aromatic tertiary amine Tetrahydroquinoline

Introduction The oxidative activation of a C(sp3)–H bond on an aromatic tertiary amine combined with a subsequent annulation using electron-rich alkenes has become a useful and direct tool to construct polycyclic nitrogen-containing heterocycles, such as tetrahydroquinoline,1 the skeletons of which are widely found in natural products and in biologically active substances.2 Initial examples were reported by Murahashi et al. who found that a rhodium(II)-TBHP system could efficiently catalyze the oxidative intramolecular cyclization of an aromatic tertiary amine tethered with an alkene moiety, producing a hydroisoquinoline framework.3 Also, Miura and co-workers demonstrated an iron-catalyzed oxidative coupling of N,N-dimethylanilines with vinyl ethers under an O2 atmosphere leading to tetrahydroquinoline derivatives.4 In the last decade, several groups reported that an association of many sorts of copper catalysts with TBHP effectively promoted an oxidative annulation of aromatic amines with unsaturated compounds to achieve a one-pot preparation of the complicated nitrogen-containing heterocycles.5 However, due to the electron deficient nature of the intermediates, such as a cation or a radical species, generated in an oxidative annulation involving the above examples,6 most alkenes employed as a coupling partner are limited ⇑ Corresponding author. Tel.: +81 4 7122 1092; fax: +81 4 7123 9890. E-mail address: [email protected] (N. Sakai). http://dx.doi.org/10.1016/j.tetlet.2016.10.071 0040-4039/Ó 2016 Elsevier Ltd. All rights reserved.

either to electron-rich alkenes, such as a vinyl ether5a,b and an enamine (an enamide),7 or to unactivated alkenes, such as styrene.8 Hence, the metal-catalyzed oxidative annulation of an aromatic amine with an electron-deficient alkene has not been studied extensively, and a metal catalytic system that could solve this problem remains unexplored.9,10 In 2011, Miura et al. described the copper-catalyzed annulation of N-methylanilines with electron-deficient alkenes, such as N-substituted maleimides, under an ambient atmosphere that led to tetrahydroquinolines.6,11 In this context, we reported that cobalt(II) chloride efficiently catalyzed the a-cyanation of aromatic tertiary amines in the presence of TBHP leading to b-aminonitriles.12 On the basis of the results described above, we expected that a Co(II)-TBHP oxidizing system could be applied to the annulation of aromatic tertiary amines with electron-deficient alkenes.13 In this letter, we report the preliminary results. Results and discussion Initially, an examination of the reaction conditions of oxidative annulation was performed (Table 1). On the basis of our previous work,12 a model coupling of N,N-dimethyl-p-toluidine with Nphenylmaleimide was performed using 10 mol% of CoCl2 and tbutyl hydroperoxide (TBHP) as an oxidizing agent at 60 °C for 5 h in CH3OH under an N2 atmosphere.14 Consequently, the expected annulation managed to proceed, producing tricyclic pyrrolo[3,4-

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Table 1 Examinations of the reaction conditionsa

Table 2 Scope of tertiary aromatic aminesa

Entry

CoX2

Amine (equiv)

Solv

Yield (%)b

1 2 3 4 5 6 7 8 9 10f

CoCl2 CoCl2 CoCl2 CoCl2 CoBr2 CoI2 CoCl2 CoCl2 —e CoCl2

1.0 1.0 1.0 1.0 1.0 1.0 1.5 2.0 2.0 2.0

CH3OH PhCH3 1,2-DCEc CH3CN CH3CN CH3CN CH3CN CH3CN CH3CN CH3CN

37 30 43 44 42 13 87 94 (90)d 5 83

a Standard conditions: N,N-dimethyl-p-toluidine (1.2 mmol), N-phenylmaleimide (0.6 mmol), solvent (2 mL), 60 °C, 5 h. b NMR yield. c 1,2-Dichloroethane. d Isolated yield. e Without CoCl2. f O2 atmosphere.

c]quinoline derivative 1 in a 37% yield (entry 1). The structure of tricyclic 1 was determined using the obtained spectral data, and was compared with the spectra of a relatively known compound. As a solvent effect, toluene was ineffective, but the use of 1,2dichloroethane (1,2-DCE) and acetonitrile resulted in a slight increase in the chemical yield (entries 2–4). Acetonitrile was then used as the optimal solvent. When two types of cobalt catalysts, in addition to CoCl2, were then examined, CoBr2 effectively undertook the desired oxidative annulation (entries 5 and 6). But, there is no clear reason for the decrease in the product yield, when using CoI2. From the viewpoint of economical cost, CoCl2 was chosen as the optimal catalyst. Interestingly, when an equivalent of N,Ndimethyl-p-toluidine was increased to 2.0 equiv, the yield of 1 was finally improved to 94% (entries 7 and 8), and 1 was finally isolated at a maximum yield of 90% after a common work-up. In these cases, no by-products were observed. The case without the cobalt catalyst hardly undertook the corresponding annulation, which proved the utility of the cobalt catalyst (entry 9). Also, when the reaction was conducted under an O2 atmosphere, the product yield was slightly decreased (entry 10). With the optimal conditions, the scope and limitations of the Co (II)-catalyzed annulation using several aromatic tertiary amines were examined (Table 2). The substrates with either an o-methyl group or no substituent group on the benzene ring gave the corresponding tricyclic tetrahydroquinoline derivatives 2 and 3 in relatively good yields. In the case involving a methoxy group, the product yield of 4 was slightly decreased to the moderate level. The substrates with typical electron-withdrawing groups, such as fluoro and bromo groups, yielded annulated products 5 and 6 in satisfactory yields. Also, when the reaction was conducted with m-methyl-substituted N,N-dimethylaniline, a mixture of tetrahydroquinoline derivatives 7a and 7b was obtained in a relatively good yield. Product 7b having a methyl group at the ortho-position was preferentially formed. This tendency is in agreement with the results on the basis of the stabilization of hyperconjugation.6,15 On the other hand, when the oxidative coupling was conducted with unsymmetrical N-alkylated or N-arylated, such as an ethyl, a benzyl, or a phenyl group, N-methylanilines under the optimal condi-

a

Standard conditions: a tertiary amine (2 mmol), N-phenylmaleimide (1 mmol), CoCl2 (0.1 mmol), TBHP (1.5 mmol), CH3CN (3 mL), 60 °C, 5 h. b Determined by1H NMR. c 0.6 mmol scale. d A complicated mixture.

tions, the expected annulation selectively proceeded at the methyl group side, giving tetrahydroquinoline derivatives 8, 9, and 10. This was probably due to an avoidance of a steric hindrance. However, all cases yielded the tricyclic adducts in rather low yields. Moreover, the substrate with a cyclic amino group as a piperidine ring led to a substantial decrease in the product yield, producing 11 in a 19% yield. Thus, N-phenyl-1,2,3,4-tetrehydroisoquinoline was employed in the hope of stabilizing the reaction intermediate with the adjacent benzene ring. Although smooth consumption of the starting amine was observed, the desired annulation did not occur to produce 12, which finally led to a complicated mixture. The scope and limitations of maleimide derivatives were then investigated using the optimal conditions (Table 3). For example, when the annulation was carried out with N-arylated maleimides with either a p-Me-C6H4 or a p-Cl-C6H4 group, the corresponding tetrahydroquinoline derivatives 13 and 14 were obtained in good yields, which led to the fact that the electronic effects of the substituents on the benzene ring had a little effect on the product yield. Also, the use of N-alkylated maleimides with either a benzyl or a t-butyl group produced annulated products 15 and 16 in satisfactory yields. Unfortunately, other electron-deficient alkenes, such as maleic anhydride, an acrylate ester, and acrylonitrile, were not applicable to the present annulation.

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Table 3 Scope of maleimide derivativesa

a

Standard conditions: N,N-dimethyl-p-toluidine (2 mmol), a maleimide (1 mmol), CoCl2 (0.1 mmol), TBHP (1.5 mmol), CH3CN (3 mL), 60 °C, 5 h. b 0.5 mmol scale. Scheme 3. Plausible reaction path for the Co(II)-TBHP-catalyzed oxidative annulation.

Scheme 1. Oxidative coupling of N,N-dimethyl-p-toluidine with an electron-rich alkene.

aromatic tertiary amine to form a radical cation species, followed by the elimination of a proton from the radical cation to form radical intermediate A.16 When using an N-substituted maleimide (path a), a radical annulation would occur, finally producing the corresponding tricyclic tetrahydroquinoline derivative. In contrast, when using an electron-rich alkene (path b), an additional oxidation would occur to form an iminium intermediate. Then, an ionic intermolecular annulation between the intermediate and the alkene would take place to produce a similar tricyclic product. Also, the released single electron in both paths would again reduce the in-situ generated cobalt(III) complex to a cobalt(II) complex to re-construct the catalytic cycle. Conclusions

Scheme 2. Control experiment with a radical scavenger.

The present oxidizing system was then applied to the coupling with an electron-rich alkene (Scheme 1). For example, when N,Ndimethyl-p-toluidine was treated with 3,4-dihydropyran under the optimal conditions, the corresponding oxidative coupling proceeded to yield tricyclic pyrano[3,2-c]quinoline derivative 17 in a 40% isolated yield. The reaction proceeded with high regioselectivity to yield the corresponding single stereoisomer. The structure of 17 was determined by the obtained spectral data, and in comparison with the NMR spectra of a known similar tricyclic derivative.5a Moreover, to confirm the plausible reaction path of the series of oxidative coupling, the standard reaction was conducted under optimal conditions in the presence of a radical scavenger, 2,6-di (tert-butyl)-p-cresol (BHT) (Scheme 2). Consequently, a substantial decrease in the yield of isoquinoline derivative 1 strongly implied that the annulation series partially involves a single electron transfer (SET) step. We assumed that the Co(II)-catalyzed oxidative annulation would proceed through Scheme 3. A plausible explanation would involve the initial generation of a t-butylperoxy radical from a cobalt (II) catalyst and TBHP. The radical would then oxidize an

We have demonstrated the cobalt(II)–TBHP oxidative annulation of several aromatic tertiary amines with a typical electrondeficient alkene, N-arylated or N-alkylated maleimide derivatives, leading to the facile preparation of a tricyclic tetrahydroquinoline framework, the structure of which constitutes important and attractive skeletons in medicinal and pharmaceutical chemistry. Also, we have found that this oxidizing system could be applied to annulation with an electron-rich alkene, 3,4-dihydropyrane. Further investigation into the extension of a coupling partner for the annulation is now in progress. Supplementary data Supplementary data (copies of the 1H and 13C NMR spectra of the derivatives that were produced by this procedure were supplied) associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.tetlet.2016.10.071. References and notes 1. For example, see: (a) Sridharan, V.; Suryavanshi, P. A.; Menéndez, J. C. Chem. Rev. 2011, 111, 7157–7259; (b) Kravchenko, D. V.; Kuzovkova, Y. A.; Kysil, V. M.; Tkachenko, S. E.; Maliarchouk, S.; Okun, I. M.; Balakin, K. V.; Ivachtchenko, A. V. J. Med. Chem. 2005, 48, 3680–3683.

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2. For selected reviews of a metal-catalyzed oxidative C(sp3)-H activation of aromatic tertiary amines, see: (a) Murahashi, S. I.; Zhang, D. Chem. Soc. Rev. 2008, 37, 1490–1501. and references cited therein; (b) Li, C. J. Acc. Chem. Res. 2008, 42, 335–344. and references cited therein. 3. Murahashi, S.; Naota, T.; Yonemura, K. J. Am. Chem. Soc. 1988, 110, 8256–8258. 4. Murata, S.; Miura, M.; Nomura, M. J. Org. Chem. 1989, 54, 4700–4702. 5. (a) Kawade, R. K.; Huple, D. B.; Lin, R.-J.; Liu, R.-S. Chem. Commun. 2015, 51, 6625–6628; (b) Huang, L.; Zhang, X.; Zhang, Y. Org. Lett. 2009, 11, 3730–3733; (c) Yang, X.; Xi, C.; Jiang, Y. Molecules 2006, 11, 978–987. 6. Nishino, M.; Hirano, K.; Satoh, T.; Miura, M. J. Org. Chem. 2011, 76, 6447–6451. and references cited therein. 7. (a) Zhao, M.-N.; Yu, L.; Hui, R.-R.; Ren, Z.-H.; Wang, Y.-Y.; Guan, Z.-H. ACS Catal. 2016, 6, 3473–3477; (b) Min, C.; Sanchawala, A.; Seidel, D. Org. Lett. 2014, 16, 2756–2759. 8. For recent selected papers of an oxidative annulation of aromatic amines with electron-rich alkenes (an oxidative Povarov-type reaction), see: (a) Liu, J.; Liu, F.; Zhu, Y.; Ma, X.; Jia, X. Org. Lett. 2015, 17, 1409–1412; (b) Wang, Y.; Peng, F.; Liu, J.; Huo, C.; Wang, X.; Jia, X. J. Org. Chem. 2015, 80, 609–614; (c) Huo, C.; Xie, H.; Wu, M.; Jia, X.; Wang, X.; Chen, F.; Tang, J. Chem. Eur. J. 2015, 21, 5723– 5726; (d) Huo, C.; Yuan, Y.; Wu, M.; Jia, X.; Wang, X.; Chen, F.; Tang, J. Angew. Chem., Int. Ed. 2014, 53, 13544–13547; (e) Jia, X.; Peng, F.; Qing, C.; Huo, C.; Wang, X. Org. Lett. 2012, 14, 4030–4033; (f) Richter, H.; García Mancheño, O. Org. Lett. 2011, 13, 6066–6069. 9. Murata, S.; Teramoto, K.; Miura, M.; Nomura, M. Heterocycles 1993, 36, 2147– 2153. 10. For examples of an oxidative annulation of aromatic amines with electrondeficient alkenes in the presence of benzoyl peroxide, see: (a) Roy, R. B.; Swan, G. A. J. Chem. Soc. C 1969, 1886–1891; (b) Roy, R. B.; Swan, G. A. Chem. Commun. 1968, 1446–1447. 11. For examples of the similar annulation of tertiary amines with maleimides, see: (a) Nicholls, T. P.; Constable, G. E.; Robertson, J. C.; Gardiner, M. G.;

12. 13.

14.

15. 16.

Bissember, A. C. ACS Catal. 2016, 6, 451–457; (b) Yadav, A. K.; Yadav, L. D. S. Tetrahedron Lett. 2016, 57, 1489–1491; (c) Liang, Z.; Xu, S.; Tian, W.; Zhang, R. Beilstein J. Org. Chem. 2015, 11, 425–430; (d) Tang, J.; Grampp, G.; Liu, Y.; Wang, B.-X.; Tao, F.-F.; Wang, L.-J.; Liang, X.-Z.; Xiao, H.-Q.; Shen, Y.-M. J. Org. Chem. 2015, 80, 2724–2732; (e) Ju, X.; Li, D.; Li, W.; Yu, W.; Bian, F. Adv. Synth. Catal. 2012, 354, 3561–3567. Sakai, N.; Mutsuro, A.; Ikeda, R.; Konakahara, T. Synlett 2013, 1283–1285. For recent examples of an oxidative conversion using a cobalt-TBHP oxidizing system, see: (a) Yu, J.; Zhang-Negrerie, D.; Du, Y. Eur. J. Org. Chem. 2016, 2016, 562–568; (b) Kong, D.-L.; Cheng, L.; Yue, T.; Wu, H.-R.; Feng, W.-C.; Wang, D.; Liu, L. J. Org. Chem. 2016, 81, 5337–5344; (c) Zhu, T.-H.; Xu, X.-P.; Cao, J.-J.; Wei, T.-Q.; Wang, S.-Y.; Ji, S.-J. Adv. Synth. Catal. 2014, 356, 509–518; (d) Zhang, F.; Du, P.; Chen, J.; Wang, H.; Luo, Q.; Wan, X. Org. Lett. 2014, 16, 1932–1935. General procedure for a cobalt(II)-catalyzed annulation of aromatic tertiary amines with N-substituted maleimides: To a screw-capped vial (5 mL) containing freshly distilled MeCN (2.0 mL) was successively added CoCl2 (6.5 mg, 0.050 mmol), an aromatic tertiary amine (1 mmol), an Nsubstituted maleimide (0.5 mmol), and 5.5 M TBHP in decane solution (0.75 mmol) under N2 atmosphere. After the tube was sealed with a cap that contained a PTFE septum, the resultant mixture was stirred at 60 °C (bath temperature). After cooling to room temperature, the mixture was passed through a silica gel-packed short column (EtOAc as the eluent), and the filtrate was removed under reduced pressure. The residue was purified by silica gel column chromatography (hexane/EtOAc = 5:1) to give the corresponding tetrahydroquinoline derivative. If necessary, the isolated product was further purified by a preparative HPLC equipped with a GPC column (chloroform as the eluent). Vallée, F.; Mousseau, J. J.; Charette, A. B. J. Am. Chem. Soc. 2010, 132, 1514–1516. For a related mechanistic aspect, see: (a) Ratnikov, M. O.; Doyle, M. P. J. Am. Chem. Soc. 2013, 135, 1549–1557; (b) Boess, E.; Schmitz, C.; Klussmann, M. J. Am. Chem. Soc. 2012, 134, 5317–5325.