Transfer of Chirality in the Rhodium-Catalyzed Chemoselective and

May 22, 2017 - By taking advantage of chirality-transfer strategy, a chemo- and regioselective allylic alkylation of naphthols and phenols with vinyla...
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Transfer of Chirality in the Rhodium-Catalyzed Chemoselective and Regioselective Allylic Alkylation of Hydroxyarenes with Vinyl Aziridines Tao-Yan Lin, Hai-Hong Wu, Jian-Jun Feng,* and Junliang Zhang* Shanghai Key Laboratory of Green Chemistry and Chemical Processes, School of Chemistry and Molecular Engineering, East China Normal University, 3663 North Zhongshan Road, Shanghai 200062, P. R. China S Supporting Information *

ABSTRACT: By taking advantage of chirality-transfer strategy, a chemoand regioselective allylic alkylation of naphthols and phenols with vinylaziridines provides an atom-economic and efficient method for the synthesis of enantioenriched 2-vinyl-2-arylethylamine derivatives. Use of readily available starting materials, a broad substrate scope, high selectivity, mild reaction conditions, as well as versatile functionalizations of the aromatic ethylamine products make this approach very practical and attractive.

date, only a few examples of intermolecular C-arylation of vinylaziridines have been reported. In 1994, the Hudlicky research group has done pioneering work on the organocoppermediated ring-opening reactions of cyclic vinylaziridines for synthesis of 2-vinyl-2-arylethylamines (Scheme 1, eq 1).5e,f Besides nucleophilic ring openings with organometal reagents, ring-opening reaction by SN2 hydroarylation of heteroaromatics (indoles) has been reported by the same group for the synthesis of β-carboline-1-one analogue (Scheme 1, eq 1).5g,h On the other hand, BF3−Et2O-promoted Friedel−Crafts reactions of acyclic vinylaziridines with electron-rich arenes have been reported by Nagumo and co-workers. However, 0.5 equiv of BF3−Et2O had to be utilized, and the reaction afforded the product as a mixture of regioisomers in some cases. Notably, with respect to substrate scope, the π-nucleophiles utilized in Nagumo’s work were limited to anisole derivatives (Scheme 1, eq 2).5i Very recently, Chiu et al. have described an elegant intermolecular Friedel−Crafts alkylation of aziridinyl enolsilane with 1,3,5-trimethoxybenzene in which, unfortunately, the corresponding SN2′ ring-opening product was also obtained as a side product (Scheme 1, eq 3).5j Although the above ring-opening reaction of vinylaziridines with C-nucleophiles is an efficient method for synthesis of 2-vinyl-2arylethylamines, we are not aware of reactions of naphthols (or phenols) with vinylaziridines to give the valuable aminonaphthols (or aminophenols), which are found in a number of natural and synthetic molecules with a wide array of interesting biological activities.6 In line with our interest in developing efficient synthesis of functionalized phenol derivatives7a,b and stereospecific ringopening of vinylaziridines,7c−e we became interested in whether naphthols (or phenols) could be employed as C-nucleophiles rather than O-nucleophiles in the intermolecular ring-opening

A romatic ethylamine derivatives are found to possess prominent biological activities and are commonly used as drugs to treat diseases such as depression, asthma, or allergies (Figure 1).1 For

Figure 1. 2-Arylethylamine scaffold in biologically active compounds.

example, well-known adrenaline, noradrenaline, oxidopamine, mescaline, amphetamine, and venlafaxine are structurally based on the 2-phenylethylamine scaffold. Besides achiral 2-phenylethylamines, β-substituted 2-arylethylamines represent an important subclass of aromatic ethylamine derivatives with high biological activity.1 Not surprisingly, they often exhibit biological enantiospecificity.2 Therefore, the development of new stereoselective strategies to access enantioenriched functionalized β-substituted 2-arylethylamines remains highly desirable. In this context, a number of methodologies for the asymmetric construction of such a skeleton have been developed.3 Among them, the reaction of aziridines with nucleophilic reagents has been and continues to be a powerful method for the introduction of an aminoethyl group.4 In contrast to the well-investigated studies on the ring-opening reactions of aryl- or alkylaziridines with nucleophiles for synthesis of aromatic ethylamines, the nucleophilic ring-opening involving vinylaziridines, some of the versatile synthons of aziridine derivatives, still lags behind.5 To © 2017 American Chemical Society

Received: April 14, 2017 Published: May 22, 2017 2897

DOI: 10.1021/acs.orglett.7b01136 Org. Lett. 2017, 19, 2897−2900

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Organic Letters Scheme 2. Survey the Scope of Vinylaziridinesa,b

Scheme 1. Synthesis of Aromatic Ethylamines by Intermolecular Ring-Opening Reactions of Vinylaziridines

a Reaction conditions: 1 (0.2 mmol), 2a (0.3 mmol), [Rh(NBD)2]+BF4− (5 mol %), CH2Cl2 (2.5 mL), at 25 °C for 15−20 min. bIsolated yield and the ee value were determined by HPLC with a chiral stationary phase.

(1e), or phenyl (1f) groups. However, contrary to 1b, the erosion of the ee value (4−17%) was observed in the reactions involving 1a, 1e, and 1f. Moreover, both aryl (1g) and alkyl (1h) groups in the R3 position were also tolerated under the current reaction conditions, but the significant erosion of ee was observed for the former reaction. Notably, the substrate (S,E)1i, which has four reactive positions for nucleophilic attacks was found to be a suitable substrate, yielding the corresponding product (S,E)-3ia as a single regioisomer in 94% yield and with retention of ee. Next, we turned our attention to investigate the scope of the current reaction with respect to various substituted naphthols and phenols (Scheme 3). This protocol is amenable to a variety of 2-naphthols bearing different R4 substituents, including hydroxyl (2b), aryl (2c, 2d, and 2h−j), allyl (2e), halogen (2g), and OMe (2k) groups at the C3−C7 positions of 2naphthols, and led to the corresponding chiral arylated ethylamines, with structural diversity, in moderate to excellent yields (67−99%) with highly efficient chirality transfer. In general, substrates with an electron-withdrawing group showed lower yield and ee value than the other substrates bearing an electron-donating group (2f versus 2g, 2i versus 2j). Encouraged by the success of 2-naphthols as C-nucleophiles in this ringopening reaction, we next tested the reaction of 1-naphthol 2l with (R)-1a. Unfortunately, this reaction delivered (R)-3al in poor yield with erosion of the ee value (15% ee decreasing). However, substrate 2m bearing an electron-donating group could be utilized in this reaction to afford the product (R)-3am in higher yield and with a slight decrease of ee value (5% ee decreasing). In addition, the phenols 2n−p could also serve as suitable aromatic nucleophiles to react with (R)-1a, delivering the desired chiral 2-(o-hydroxyaryl)-2-vinylethylamines in considerable yields with complete chirality transfer. Besides phenol derivatives, the reaction remained efficient when electron-rich arene 4a was used as a substrate, providing the corresponding (R)-5aa as a single regioisomer. Of note, the Oalkylated rather than C-alkylated product was obtained when we subjected 4-methoxyphenol (or phenol) and (R)-1a to the current reaction conditions (Scheme 4). The rich functionalities in product 3 provide many opportunities for further synthetic transformations. The double bond in (R)-3aa could be hydrogenated to furnish product 7aa in

reactions of chiral vinylaziridines to give the enantioenriched functionalized arylethylamine products through a chiralitytransfer strategy (Scheme 1, eq 4).8 However, this hypothesis may face considerable challenges, such as the following. (1) Although O-nucleophilic ring-opening of aziridines with phenol derivatives is well documented, research on the ortho-Calkylation of phenol with aziridine is relatively rare.9 (2) Compared to protected hydroxyarenes, both C-nucleophilic and O-nucleophilic ring openings can be involved in the reaction of unprotected hydroxyarenes with vinylaziridines.10 (3) While ring-opening reactions of arylaziridines with π-nucleophiles tend to proceed selectively at a benzylic position, there are up to four reactive positions for nucleophilic attack with respect to vinylaziridines. Thus, the challenge is how to control the regioselectivity. (4) Besides these, the other problem that needs to be solved is how to enhance the efficiency of chirality transfer. To examine the above hypothesis, vinylaziridine (R)-1a (98% ee) and 2-naphthol 2a were selected as the model substrates. As shown in Table S1, (R)-1a decomposed quickly when Sc(OTf)3, Mg(OTf)2, Yb(OTf)3, In(OTf)3, Cu(OTf)2, or Bi(OTf)3 was used as the catalyst, even though these are commonly used in Friedel−Crafts alkylation of π-nucleophile with alkyl- or arylaziridine.4 After many attempts, we were pleased to find that the C-alkylated product (R)-3aa could be obtained in 96% NMR yield and 94% ee in the presence of 5 mol % of [Rh(NBD)2]BF4 in CH2Cl2 at 25 °C. With the optimal mild reaction conditions in hand, we then turned to explore the generality of this ring-opening process with a variety of vinylaziridines with 2a (Scheme 2). The substituents on nitrogen of the aziridines can be tosyl, nosyl, and mesyl groups (1b−d). In all cases, the expected 2-vinyl-2-arylethylamines were obtained in moderate to excellent yields with complete chirality transfer (3ba−da). The structure and absolute configuration of (R)-3ba were unambiguously determined by X-ray crystallographic analysis.11 Besides R2 = H (1b), the substituents on the olefin moiety of vinylaziridine can be either methyl (1a), n-butyl 2898

DOI: 10.1021/acs.orglett.7b01136 Org. Lett. 2017, 19, 2897−2900

Letter

Organic Letters Scheme 3. Survey of the Scope of Naphthols and Phenolsa

Scheme 5. Synthetic Transformations

Scheme 6. Control Experiments

Scheme 7. Proposed Mechanism

a

Reaction conditions are the same as those described in Scheme 2. Isolated yield and the ee value was determined by HPLC with a chiral stationary phase. b1,3,5-Trimethoxybenzene was used as the nucleophilic reagent.

Scheme 4. O-Nucleophilic Ring-Opening of (R)-1a with Phenols 2q and 2r B and further reacts with B through allylic dearomatization of naphthols to generate intermediate C with a net inversion of absolute configuration and regenerate the rhodium catalyst.12 Finally, intermediate C underwent aromatization to afford the desired product 3. Alternatively, instead of the nucleophilic substitution, intermediate B can first isomerize to B′, from which the erosion of the ee value would be observed. To summarize, we have demonstrated that hydroxyarenes can serve as a C-nucleophiles rather than O-nucleophiles in rhodiumcatalyzed regioselective ring-opening reactions of vinylaziridines. The reaction provides an efficient, straightforward, and atomeconomic route to functionalized 2-arylethylamines in an enantioselective manner by a chirality-transfer strategy. Further mechanism and synthetic application studies of this efficient transformation are underway.

quantitative yield. The selective protection of phenolic hydroxyl group was realized by treatment of (R)-3aa with allyl bromide and K2CO3. Moreover, (R)-3aa can be transformed into a useful heterocycle, dihydrobenzofuran 9aa, in the presence of TsOH− H2O in 93% yield without loss of enantiometric purity. Compound 10aa was also obtained in reasonable yield and ee value by PhI(OAc)2-mediated oxidative dearomatization of naphthols. Besides these, the p-nosyl group in 3ca was easily removed in the presence of PhSH/K2CO3 (Scheme 5). To gain additional insight into the mechanism, we performed control experiments (Scheme 6). The reaction was found to be messy, and (R)-1a decomposed quickly when 2-methoxynaphthalene 12 was employed in the current reaction, while the Oalkylated product 14 could be accessed exclusively from (R)-1a and 13 under the standard reaction conditions. Based on the above results and our previous mechanistic studies,7c−e a plausible mechanism is proposed in Scheme 7. Coordination of rhodium catalyst to vinylaziridine (R)-1 via the olefin and the nitrogen gives complex A. Subsequent oxidative addition with retention gives enyl (σ+π) rhodium species B and B′.8 Then, the naphthol 2 is deprotonated by the amide anion in

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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.7b01136. Experimental procedures, 1H and 13C NMR spectra, and HPLC data for all new products (PDF) X-ray crystallographic data for (R)-3ba (CIF) 2899

DOI: 10.1021/acs.orglett.7b01136 Org. Lett. 2017, 19, 2897−2900

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Organic Letters

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4037. (f) Hudlicky, T.; Tian, X.; Königsberger, K.; Maurya, R.; Rouden, J.; Fan, B. J. Am. Chem. Soc. 1996, 118, 10752. (g) Rinner, U.; Hudlicky, T.; Gordon, H.; Pettit, G. R. Angew. Chem., Int. Ed. 2004, 43, 5342. (h) Hudlicky, T.; Rinner, U.; Finn, K.; Ghiviriga, I. J. Org. Chem. 2005, 70, 3490. (i) Nagumo, S.; Takada, H.; Yasui, E.; Sahara, Y.; Chinen, Y.; Tanaka, H.; Morita, Y.; Kobiki, C.; Narisawa, D.; Mizukami, M.; Miyashita, M. Heterocycles 2011, 83, 555. (j) Ling, J.; Lam, S. K.; Lo, B.; Lam, S.; Wong, W.-K.; Sun, J.; Chen, G.; Chiu, P. Org. Chem. Front. 2016, 3, 457. (6) (a) Szatmári, I.; Martinek, T. A.; Lázár, L.; Fülöp, F. Eur. J. Org. Chem. 2004, 2004, 2231. (b) Szatmári, I.; Hetényi, A.; Lázár, L.; Fülöp, F. J. Heterocycl. Chem. 2004, 41, 367. (c) Turgut, Z.; Pelit, E.; Koycu, A. Molecules 2007, 12, 345. (7) (a) Yu, Z.; Ma, B.; Chen, M.; Wu, H.-H.; Liu, L.; Zhang, J. J. Am. Chem. Soc. 2014, 136, 6904. (b) Yu, Z.; Li, Y.; Shi, J.; Ma, B.; Liu, L.; Zhang, J. Angew. Chem., Int. Ed. 2016, 55, 14807. (c) Feng, J.-J.; Lin, T.Y.; Zhu, C.-Z.; Wang, H.; Wu, H.-H.; Zhang, J. J. Am. Chem. Soc. 2016, 138, 2178. (d) Lin, T.-Y.; Zhu, C.-Z.; Zhang, P.; Wang, Y.; Wu, H.-H.; Feng, J.-J.; Zhang, J. Angew. Chem., Int. Ed. 2016, 55, 10844. (e) Zhu, C.Z.; Feng, J.-J.; Zhang, J. Angew. Chem., Int. Ed. 2017, 56, 1351. (8) For the pioneering work on the enyl (σ+π) rhodium species, see: (a) Evans, P. A.; Nelson, J. D. J. Am. Chem. Soc. 1998, 120, 5581. For recent work on rhodium-catalyzed allylic substitution reaction, see: (b) Evans, P. A.; Oliver, S.; Chae, J. J. Am. Chem. Soc. 2012, 134, 19314. (c) Turnbull, B. W. H.; Oliver, S.; Evans, P. A. J. Am. Chem. Soc. 2015, 137, 15374. (d) Evans, P. A.; Uraguchi, D. J. Am. Chem. Soc. 2003, 125, 7158. (e) Evans, P. A.; Leahy, D. K. J. Am. Chem. Soc. 2000, 122, 5012. (f) Wright, T. B.; Evans, P. A. J. Am. Chem. Soc. 2016, 138, 15303. (g) Loh, C. C. J.; Schmid, M.; Webster, R.; Yen, A.; Yazdi, S. K.; Franke, P. T.; Lautens, M. Angew. Chem., Int. Ed. 2016, 55, 10074. For review, see: (h) Lautens, M.; Fagnou, K.; Hiebert, S. Acc. Chem. Res. 2003, 36, 48. (i) Leahy, D. K.; Evans, P. A. In Modern Rhodium-Catalyzed Organic Reactions; Evans, P. A., Ed.; Wiley-VCH: Weinheim, 2005; Vol. 10, pp 191−214. (9) C−C coupling of electron-rich aryl borates with aryl aziridines for synthesis of 2-arylethylamines; see: Pineschi, M.; Bertolini, F.; Crotti, P.; Macchia, F. Org. Lett. 2006, 8, 2627. (10) O-Nucleophilic ring-opening of aryl- or alkylaziridines with phenol derivatives: (a) Ghorai, M. K.; Nanaji, Y. J. Org. Chem. 2013, 78, 3867. (b) Llaveria, J.; Espinoza, A.; Negrón, G.; Matheu, M. I.; Castillón, S. Tetrahedron Lett. 2012, 53, 2525. (c) Bhadra, S.; Adak, L.; Samanta, S.; Islam, A. K. M. M.; Mukherjee, M.; Ranu, B. C. J. Org. Chem. 2010, 75, 8533. For reviews of O-allylation of phenols, see: (d) Trost, B. M.; Crawley, M. L. Chem. Rev. 2003, 103, 2921. (e) Lu, Z.; Ma, S. Angew. Chem., Int. Ed. 2008, 47, 258. (11) CCDC 1543703 ((R)-3ba) contains the supplementary crystallographic data for this paper. These data can be obtained free of charge from the Cambridge Crystallographic Data Centre via www.ccdc.cam. ac.uk/data_request/cif. (12) Selected examples for asymmetric allylic dearomatization of phenol derivatives, see: (a) Wu, Q.-F.; Liu, W.-B.; Zhuo, C.-X.; Rong, Z.Q.; Ye, K.-Y.; You, S.-L. Angew. Chem., Int. Ed. 2011, 50, 4455. (b) Zhuo, C.-X.; You, S.-L. Angew. Chem., Int. Ed. 2013, 52, 10056. (c) Tu, H.-F.; Zheng, C.; Xu, R.-Q.; Liu, X.-J.; You, S.-L. Angew. Chem., Int. Ed. 2017, 56, 3237. (d) Nemoto, T.; Ishige, Y.; Yoshida, M.; Kohno, Y.; Kanematsu, M.; Hamada, Y. Org. Lett. 2010, 12, 5020. For reviews, see: (e) Zhuo, C.-X.; Zheng, C.; You, S.-L. Acc. Chem. Res. 2014, 47, 2558. (f) Zhuo, C.-X.; Zhang, W.; You, S.-L. Angew. Chem., Int. Ed. 2012, 51, 12662.

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. ORCID

Jian-Jun Feng: 0000-0002-6094-3268 Junliang Zhang: 0000-0002-4636-2846 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We grateful for the funding support from the National Natural Science Foundation of China (21602062, 21373088, 21425205), the Ministry of Education (IRT-16R25), and the Shanghai Sailing Program (15YF1403600).

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DOI: 10.1021/acs.orglett.7b01136 Org. Lett. 2017, 19, 2897−2900