Letter Cite This: Org. Lett. XXXX, XXX, XXX−XXX
pubs.acs.org/OrgLett
Phenanthrene Synthesis by Palladium(II)-Catalyzed γ‑C(sp2)−H Arylation, Cyclization, and Migration Tandem Reaction Bo-Bo Gou,† Hui Yang,† Huai-Ri Sun,† Jie Chen,*,† Junliang Wu,*,‡ and Ling Zhou*,† †
Org. Lett. Downloaded from pubs.acs.org by AUSTRALIAN NATL UNIV on 12/13/18. For personal use only.
Key Laboratory of Synthetic and Natural Functional Molecule Chemistry of Ministry of Education, College of Chemistry & Materials Science, National Demonstration Center for Experimental Chemistry Education, Northwest University, Xi’an 710127, P. R. China ‡ College of Chemistry and Molecular Engineering, Zhengzhou University, Zhengzhou 450001, P. R. China S Supporting Information *
ABSTRACT: Phenanthrene is an important structural motif in chemistry and materials science, and many synthetic routes have been developed to construct its skeleton. However, synthesis of unsymmetric phenanthrenes remains a challenge. Here, an efficient one-pot tandem reaction for the preparation of phenanthrenes via sequential γ-C(sp2)−H arylation, cationic cyclization, dehydration, and 1,2-migration was developed. A wide range of symmetric and unsymmetric phenanthrenes with diversified functional groups were synthesized with good to excellent yields.
P
avoid issues with regioselectivity (Scheme 1a).3,4 Furthermore, arylalkynes were usually employed in those procedures, and alkylalkynes always encountered low yields with side products.3 Thus, developing efficient methods for the selective synthesis of phenanthrenes is highly desirable. Inspired by previous work on the transient directing group assisted Pd-catalyzed C(sp2)−H arylation reactions,6 we envisioned that Pd-catalyzed γ-C(sp2)−H arylation of phenylacetaldehydes with aryl iodide by using an amino acid as a transient directing group would produce biaryl-2-ylacetaldehydes and release 1 equiv of H+, and biaryl-2-ylacetaldehydes would undergo sequential intramolecular cationic cyclization, dehydration, and 1,2-migration in the presence of an acid to generate phenanthrenes (Scheme 1b).7 The major challenges of this strategy arise from questions regarding whether the acid generated during the course of the reaction is sufficiently reactive to trigger the following cascade reaction and selective 1,2-migration to give a single isomer of phenanthrenes. To test this hypothesis, a Pd-catalyzed reaction of 2-methyl2-phenylpropanal (1a) and iodobenzene (2a) by using glycine (L1) as the transient directing group was examined in the presence of a stoichiometric amount of AgTFA in a mixed solvent (hexafluoroisopropanol (HFIP)/AcOH, 9/1) in air at 105 °C for 16 h. To our delight, the desired C−H arylation and cyclization product phenanthrene 3a was obtained in 35% yield (Table 1, entry 1). To improve the yield of this reaction, a screening of different ligands (L1−5) was first carried out (entries 1−5). Glycine gave the best yield of 3a; L2−4 significantly decreased the yield; and no reaction was detected when L5 was used. A control experiment without using the transient directing group gave no desired product formation (entry 6). It was noticed that the yield was clearly increased
henanthrene is one of the most commonly encountered polycyclic aromatic structures for materials science and medicinal chemistry.1 Owing to their unique physical properties and bioactivities, intensive efforts on the construction of phenanthrene skeletons have been made.2−5 Early established procedures such as intramolecular McMurry coupling, olefin metathesis, and photocyclization reactions suffer from many drawbacks, including harsh reaction conditions and a tedious multistep process for the preparation of starting materials.2 Recently, metal-catalyzed annulations of biaryl derivatives3,4 and multicomponent reactions5 for the synthesis of phenanthrenes have been well documented (Scheme 1a), wherein [4 + 2] reaction with alkynes was one of the most efficient strategies. Many biaryl reactants are prefunctionalized, bearing various functional groups that enable participation in this reaction. However, selective synthesis of unsymmetric phenanthrenes is still a big challenge. Symmetric biaryls (Ar1 = Ar2) or symmetric alkynes (R1 = R2) were generally used to Scheme 1. Metal-Catalyzed Construction of Phenanthrenes
Received: November 2, 2018
© XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.8b03511 Org. Lett. XXXX, XXX, XXX−XXX
Letter
Organic Letters Table 1. Optimization of the Reaction Conditionsa
Pd
ligand (mol %)
1
Pd(OAc)2
L1 (40)
2
Pd(OAc)2
L2 (40)
3
Pd(OAc)2
L3 (40)
4
Pd(OAc)2
L4 (40)
5
Pd(OAc)2
L5 (40)
6
Pd(OAc)2
-
7
Pd(OAc)2
L1 (40)
8
Pd(OAc)2
L1 (40)
9 10 11 12 13 14 15c 16d 17e 18 19f 20f,g
Pd(OAc)2 Pd(TFA)2 Pd(PPh3)2Cl2 [PdCl(η3-C3H5)]2 PdCl2 Pd(OAc)2 Pd(OAc)2 Pd(OAc)2 Pd(OAc)2 Pd(OAc)2 Pd(OAc)2
L1 L1 L1 L1 L1 L1 L1 L1 L1 L1 L1 L1
entry
(40) (40) (40) (40) (40) (40) (40) (40) (40) (32) (32) (32)
solvent (v/v) HFIP/AcOH (9/1) HFIP/AcOH (9/1) HFIP/AcOH (9/1) HFIP/AcOH (9/1) HFIP/AcOH (9/1) HFIP/AcOH (9/1) HFIP/AcOH (3/1) HFIP/AcOH (30/1) HFIP HFIP HFIP HFIP HFIP HFIP HFIP HFIP HFIP HFIP HFIP HFIP
Scheme 2. Scope of the Reaction (Ar1 ≠ Ar2)a
yield (%)b 35 10 6 8 26 49 63 58 49 36 72 91 90
a
Reaction conditions: 1a (0.2 mmol), 2 (0.5 mmol), Pd(OAc)2 (12 mol %), L1 (32 mol %), AgTFA (0.32 mmol), HFIP (1.0 mL), 16 h, air. Yield of isolated product. b5.0 mmol scale. cFor 19 h. dFor 22 h.
iodides were also good substrates for this transformation (3f− h, 3m−o). The tolerance of the halogens provided great potential to produce more complex structures through crosscoupling reactions. Besides, 3p with a chrysene structure was also obtained when 2-iodonaphthalene was employed. It is worth noting that different reaction temperatures were used, probably because of the electronic effect from various substituents.8,9 Then diversely substituted phenyl moieties of aldehydes were tested. Different substituted groups with electron-donating (3b, 3d, 3l, 3s), halogen (3g−h, 3m−o, 3w−3ab), as well as phenyl groups (3r) in the benzene ring of aldehydes were examined; all the reactions proceeded smoothly to afford the corresponding phenanthrenes in good yields. To evaluate the practicality of this catalytic process, gram-scale reaction of 1a was carried out. As a result, the desired product 3a was successfully obtained in 90% yield (Scheme 2). Next, the substrate scope of the reaction with respect to the α,α-disubstituted aldehydes was investigated (Scheme 3). The desired symmetric 9,10-dialkyl phenanthrenes 3ac−ae can be prepared in 65−87% yield. Importantly, unsymmetric 9,10dialkyl phenanthrenes could also be readily constructed with good yields by using this strategy (3af−an). As expected, α,αdiphenylpropylaldehyde afforded the corresponding phenanthrene 3aj in 70% yield. The substrate bearing an ester group
a
Reaction conditions: 1a (0.2 mmol), 2a (0.5 mmol), Pd(OAc)2 (0.024 mmol), ligand, AgTFA (0.32 mmol), solvent (2.0 mL), air, 105 °C, 16 h. bYield of isolated product. cAgOAc as additive. d Ag2CO3 as additive. eAg2O as additive. fSolvent (1.0 mL). gReaction was carried out under N2.
when HFIP was used as the solvent without AcOH (entries 7− 9). Then the catalyst was evaluated; Pd(TFA)2, Pd(PPh3)2Cl2, and [PdCl(η3-C3H5)]2 all provided diminished yields (entries 10−12); and PdCl2 failed to catalyze the reaction (entry 13). Expectedly, no desired product was detected in the absence of Pd catalyst (entry 14). The examination of silver salts revealed that AgOAc, Ag2CO3, and Ag2O were ineffective in the reaction (entries 15−17). A 91% yield of 3a was obtained when the reaction was conducted in HFIP (0.2 M) by using 32 mol % of L1 (entry 19). Additionally, the reaction could be smoothly implemented under atmospheric N2, showing that air has no apparent effects on this reaction (Table 1, entry 20). With the optimized conditions in hand,8 we first explored the scope of C−H arylation with various aryl iodides. As shown in Scheme 2, great functional group compatibility was observed in this catalytic process. Aryl iodides with electrondonating groups (alkoxyl or alkyl, 3b−e, 3l) or electronwithdrawing groups (CF3 or ester, 3i,j) were all compatible with the current catalytic system. Halogen-substituted aryl B
DOI: 10.1021/acs.orglett.8b03511 Org. Lett. XXXX, XXX, XXX−XXX
Letter
Organic Letters Scheme 3. Scope of the Reaction (Variation of R1, R2)a
Scheme 5. Mechanism Investigation
a
Reaction conditions: 1 (0.2 mmol), 2a (0.5 mmol), Pd(OAc)2 (12 mol %), L1 (32 mol %), AgTFA (0.32 mmol), HFIP (1.0 mL), 16 h, air. Yield of isolated product. bAt 110 °C. cUnder O2.
Scheme 4. Scope of the Reaction (R1 ≠ R2 and Ar1 ≠ Ar2)a
α-position caused ring expansion as a result of 1,2-migration. Further dehydrogenation product 3ao was observed under these reaction conditions along with the expected product 3ao′. Similarly, phenanthrene 3ap was prepared in 68% yield, which can be aromatized to triphenylene 4 smoothly.10 Furthermore, completely unsymmetric phenanthrenes, which are difficult to be synthesized by previously reported methods, were also achieved by this new strategy. As shown in Scheme 4, a series of unsymmetric phenanthrenes were prepared with good to excellent yields and exclusive regioselectivity. Satisfactorily, phenanthrenes bearing bromine atom at different positions can also be prepared efficiently (3aq, 3av−ax, 3az−bd). The excellent selectivity may be due to the electronic property of the substituents, wherein the electron-rich substituents are prone to migrate.11 The exact structures of 3ak and 3aq were confirmed by X-ray analysis. To provide some insight into the mechanism of the one-pot synthesis of phenanthrenes, we attempt to isolate the C−H arylation product. Indeed, biphenyl intermediate 5 was obtained when the reaction temperature was decreased to 90 °C (Scheme 5). The intermediate 5 was then subjected to different cyclization conditions. The desired cyclization product 3g was obtained only in 12% yield after 10 h in the absence of TFA, while a 98% yield was obtained in the presence of 1 equiv of TFA after 1.5 h. Additionally, the KIE
a
Reaction conditions: 1 (0.2 mmol), 2 (0.5 mmol), Pd(OAc)2 (12 mol %), L1 (32 mol %), AgTFA (0.32 mmol), HFIP (1.0 mL), 16 h, air. Yield of isolated product. bAt 110 °C, 18 h. cAt 120 °C.
was also suitable for this reaction (3al), while α-amine- or alkoxy-substituted substrate returned no desired product. Intriguingly, aldehydes bearing a carbocyclic structure at the C
DOI: 10.1021/acs.orglett.8b03511 Org. Lett. XXXX, XXX, XXX−XXX
Letter
Organic Letters
Tucek, J.; Zboril, R. Chem. Rev. 2015, 115, 4744. (e) Sun, Z.; Ye, Q.; Chi, C.; Wu, J. Chem. Soc. Rev. 2012, 41, 7857. (f) Wu, J.; Pisula, W.; Müllen, K. Chem. Rev. 2007, 107, 718. (g) Li, M.; An, C.; Marszalek, T.; Guo, X.; Long, Y.-Z.; Yin, H.; Gu, C.; Baumgarten, M.; Pisula, W.; Mullen, K. Chem. Mater. 2015, 27, 2218. (h) Anthony, J. E. Angew. Chem., Int. Ed. 2008, 47, 452. (i) Wang, S.; Yan, X.; Cheng, Z.; Zhang, H.; Liu, Y.; Wang, Y. Angew. Chem., Int. Ed. 2015, 54, 13068. (j) Wei, L.; Shi, Q.; Bastow, K. F.; Brossi, A.; Morris-Natschke, S. L.; Nakagawa-Goto, K.; Wu, T.-S.; Pan, S.-L.; Teng, C.-M.; Lee, K.-H. J. Med. Chem. 2007, 50, 3674. (k) Lin, J.-C.; Yang, S.-C.; Hong, T.-M.; Yu, S.-L.; Shi, Q.; Wei, L.; Chen, H.-Y.; Yang, P.-C.; Lee, K.-H. J. Med. Chem. 2009, 52, 1903. (2) (a) Martin, R. H. Angew. Chem., Int. Ed. Engl. 1974, 13, 649. (b) McMurry, J. E.; Lectka, T.; Rico, J. G. J. Org. Chem. 1989, 54, 3748. (c) Liu, L.; Yang, B.; Katz, T. J.; Poindexter, M. K. J. Org. Chem. 1991, 56, 3769. (d) Dubois, F.; Gingras, M. Tetrahedron Lett. 1998, 39, 5039. (3) (a) Larock, R. C.; Doty, M. J.; Tian, Q.; Zenner, J. M. J. Org. Chem. 1997, 62, 7536. (b) Fürstner, A.; Mamane, V. J. Org. Chem. 2002, 67, 6264. (c) Mamane, V.; Hannen, P.; Furstner, A. Chem. Eur. J. 2004, 10, 4556. (d) Wang, C.; Rakshit, S.; Glorius, F. J. Am. Chem. Soc. 2010, 132, 14006. (e) Ma, J.; Li, G.; Qiao, Y.; Tu, J.; Liu, S.; Xu, F. Synlett 2015, 26, 1991. (f) Ozaki, K.; Kawasumi, K.; Shibata, M.; Ito, H.; Itami, K. Nat. Commun. 2015, 6, 6251. (g) Matsuda, T.; Kato, K.; Goya, T.; Shimada, S.; Murakami, M. Chem. - Eur. J. 2016, 22, 1941. (h) Ito, H.; Ozaki, K.; Itami, K. Angew. Chem., Int. Ed. 2017, 56, 11144. (i) Ozaki, K.; Murai, K.; Matsuoka, W.; Kawasumi, K.; Ito, H.; Itami, K. Angew. Chem., Int. Ed. 2017, 56, 1361. (j) Ozaki, K.; Matsuoka, W.; Ito, H.; Itami, K. Org. Lett. 2017, 19, 1930. (k) Iverson, C. N.; Jones, W. D. Organometallics 2001, 20, 5745. (l) Kanno, K.-i.; Liu, Y.; Iesato, A.; Nakajima, K.; Takahashi, T. Org. Lett. 2005, 7, 5453. (m) Matsumoto, A.; Ilies, L.; Nakamura, E. J. Am. Chem. Soc. 2011, 133, 6557. (n) Lin, Y.-D.; Cho, C.-L.; Ko, C.-W.; Pulte, A.; Wu, Y.-T. J. Org. Chem. 2012, 77, 9979. (o) Nagata, T.; Hirano, K.; Satoh, T.; Miura, M. J. Org. Chem. 2014, 79, 8960. (p) Nagata, T.; Satoh, T.; Nishii, Y.; Miura, M. Synlett 2016, 27, 1707. (q) Shoji, Y.; Tanaka, N.; Muranaka, S.; Shigeno, N.; Sugiyama, H.; Takenouchi, K.; Hajjaj, F.; Fukushima, T. Nat. Commun. 2016, 7, 12704. (r) Yan, J.; Yoshikai, N. Org. Lett. 2017, 19, 6630. (4) (a) Goldfinger, M. B.; Crawford, K. B.; Swager, T. M. J. Am. Chem. Soc. 1997, 119, 4578. (b) Iuliano, A.; Piccioli, P.; Fabbri, D. Org. Lett. 2004, 6, 3711. (c) Shen, H.-C.; Tang, J.-M.; Chang, H.-K.; Yang, C.-W.; Liu, R.-S. J. Org. Chem. 2005, 70, 10113. (d) Nagao, I.; Shimizu, M.; Hiyama, T. Angew. Chem., Int. Ed. 2009, 48, 7573. (e) Komeyama, K.; Igawa, R.; Takaki, K. Chem. Commun. 2010, 46, 1748. (f) Shimizu, M.; Nagao, I.; Tomioka, Y.; Kadowaki, T.; Hiyama, T. Tetrahedron 2011, 67, 8014. (g) Bera, K.; Sarkar, S.; Jalal, S.; Jana, U. J. Org. Chem. 2012, 77, 8780. (h) Xia, Y.; Liu, Z.; Xiao, Q.; Qu, P.; Ge, R.; Zhang, Y.; Wang, J. Angew. Chem., Int. Ed. 2012, 51, 5714. (i) Carreras, J.; Gopakumar, G.; Gu, L.; Gimeno, A.; Linowski, P.; Petuškova, J.; Thiel, W.; Alcarazo, M. J. Am. Chem. Soc. 2013, 135, 18815. (j) Kwon, Y.; Cho, H.; Kim, S. Org. Lett. 2013, 15, 920. (k) Yamamoto, Y.; Matsui, K.; Shibuya, M. Chem. - Eur. J. 2015, 21, 7245. (l) Jin, R.; Chen, Y.; Liu, W.; Xu, D.; Li, Y.; Ding, A.; Guo, H. Chem. Commun. 2016, 52, 9909. (m) Shimizu, M.; Nagao, I.; Tomioka, Y.; Hiyama, T. Angew. Chem., Int. Ed. 2008, 47, 8096. (n) McAtee, C. C.; Riehl, P. S.; Schindler, C. S. J. Am. Chem. Soc. 2017, 139, 2960. (o) Matsuoka, W.; Ito, H.; Itami, K. Angew. Chem., Int. Ed. 2017, 56, 12224. (5) (a) Peña, D.; Pérez, D.; Guitián, E.; Castedo, L. J. Am. Chem. Soc. 1999, 121, 5827. (b) Catellani, M.; Motti, E.; Baratta, S. Org. Lett. 2001, 3, 3611. (c) Bhuvaneswari, S.; Jeganmohan, M.; Cheng, C.-H. Org. Lett. 2006, 8, 5581. (d) Liu, Z.; Larock, R. C. Angew. Chem., Int. Ed. 2007, 46, 2535. (e) Iwasaki, M.; Araki, Y.; Nishihara, Y. J. Org. Chem. 2017, 82, 6242. (f) Yoshikawa, E.; Yamamoto, Y. Angew. Chem., Int. Ed. 2000, 39, 173. (g) Fu, W. C.; Wang, Z.; Chan, W. T. K.; Lin, Z.; Kwong, F. Y. Angew. Chem., Int. Ed. 2017, 56, 7166. (h) Zhao, Q.; Fu, W. C.; Kwong, F. Y. Angew. Chem., Int. Ed. 2018, 57, 3381.
experiments were also conducted, and the intramolecular and intermolecular KIE values of [D1]-1a and 1a/[D5]-1a were found to be kH/kD = 1.6 and 3.8, respectively.8 These results indicate that the first step is C−H arylation to give compound A,6,12 and the C−H bond activation might be involved in the rate-determining step. Furthermore, the newly generated TFA during the C−H bond activation reaction is the catalyst of the following A to 3 cascade cyclization (Scheme 5). In summary, we have developed a straightforward and efficient procedure for the preparation of phenanthrenes from readily available starting materials via a sequence combining γC(sp2)−H arylation, cationic cyclization, dehydration, and 1,2migration. A variety of symmetric and unsymmetric phenanthrene derivatives with a high degree of functionalization including triphenylenes were synthesized by this protocol. We believe that this operationally simple protocol will be highly attractive to other chemists in manipulating phenanthrenes for materials science and organic synthesis. Further studies on elucidating the mechanism and extending the application of this protocol are underway.
■
ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.orglett.8b03511. Experimental procedures, characterization data for all new compounds, and copies of 1H and 13C NMR spectra (PDF) Accession Codes
CCDC 1868558−1868559 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing
[email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
■
AUTHOR INFORMATION
Corresponding Authors
*E-mail:
[email protected]. *E-mail:
[email protected]. *E-mail:
[email protected]. ORCID
Jie Chen: 0000-0001-6745-5534 Ling Zhou: 0000-0002-6805-2961 Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS We thank the National Natural Science Foundation of China (NSFC-21672170), the Natural Science Basic Research Plan in Shaanxi Province of China (2018JC-020, 2018JM2029), and the Key Science and Technology Innovation Team of Shaanxi Province (2017KCT-37) for financial support.
■
REFERENCES
(1) (a) Harvey, R. G. Polycyclic Aromatic Hydrocarbons; Wiley-VCH: New York, 1997. (b) Narita, A.; Wang, X.-Y.; Feng, X.; Mullen, K. Chem. Soc. Rev. 2015, 44, 6616. (c) Figueira-Duarte, T. M.; Müllen, K. Chem. Rev. 2011, 111, 7260. (d) Georgakilas, V.; Perman, J. A.; D
DOI: 10.1021/acs.orglett.8b03511 Org. Lett. XXXX, XXX, XXX−XXX
Letter
Organic Letters (6) For selected examples, see: (a) Zhang, F.-L.; Hong, K.; Li, T.-J.; Park, H.; Yu, J.-Q. Science 2016, 351, 252. (b) Liu, Y.; Ge, H. Nat. Chem. 2016, 9, 26. (c) Ma, F.; Lei, M.; Hu, L. Org. Lett. 2016, 18, 2708. (d) Wu, Y.; Chen, Y.-Q.; Liu, T.; Eastgate, M. D.; Yu, J.-Q. J. Am. Chem. Soc. 2016, 138, 14554. (e) Xu, Y.; Young, M. C.; Wang, C.-P.; Magness, D. M.; Dong, G. Angew. Chem., Int. Ed. 2016, 55, 9084. (f) Yang, K.; Li, Q.; Liu, Y.; Li, G.; Ge, H. J. Am. Chem. Soc. 2016, 138, 12775. (g) Zhu, R.-Y.; Liu, L.-Y.; Yu, J.-Q. J. Am. Chem. Soc. 2017, 139, 12394. (h) Chen, X.-Y.; Ozturk, S.; Sorensen, E. Org. Lett. 2017, 19, 6280. (i) Chen, X.-Y.; Ozturk, S.; Sorensen, E. Org. Lett. 2017, 19, 1140. (j) Liu, X.-H.; Park, H.; Hu, J.-H.; Hu, Y.; Zhang, Q.-L.; Wang, B.-L.; Sun, B.; Yeung, K.-S.; Zhang, F.-L.; Yu, J.Q. J. Am. Chem. Soc. 2017, 139, 888. (k) Yao, Q.-J.; Zhang, S.; Zhan, B.-B.; Shi, B.-F. Angew. Chem., Int. Ed. 2017, 56, 6617. (l) Xu, J.; Liu, Y.; Wang, Y.; Li, Y.; Xu, X.; Jin, Z. Org. Lett. 2017, 19, 1562. (m) Wang, D.-Y.; Guo, S.-H.; Pan, G.-F.; Zhu, X.-Q.; Gao, Y.-R.; Wang, Y.-Q. Org. Lett. 2018, 20, 1794. (n) Xu, J.; Liu, Y.; Zhang, J.; Xu, X.; Jin, Z. Chem. Commun. 2018, 54, 689. (o) Park, H.; Verma, P.; Hong, K.; Yu, J.-Q. Nat. Chem. 2018, 10, 755. (7) For acid-catalyzed cycloaromatization of carbonyl compounds, see: (a) Bradsher, C. K. J. Am. Chem. Soc. 1940, 62, 486. (b) Bradsher, C. K.; Jackson, W. J. J. Am. Chem. Soc. 1954, 76, 734. (c) Fuson, R. C.; Talbott, R. L. J. Org. Chem. 1961, 26, 2674. (d) Bradsher, C. K. Chem. Rev. 1987, 87, 1277. (e) Kuninobu, Y.; Tatsuzaki, T.; Matsuki, T.; Takai, K. J. Org. Chem. 2011, 76, 7005. (f) Fujita, T.; Takahashi, I.; Hayashi, M.; Wang, J.; Fuchibe, K.; Ichikawa, J. Eur. J. Org. Chem. 2017, 2017, 262. (8) See the Supporting Information for details. (9) (a) Fürstner, A.; Mamane, V. J. Org. Chem. 2002, 67, 6264. (b) Jin, R.; Chen, Y.; Liu, W.; Xu, D.; Li, Y.; Ding, A.; Guo, H. Chem. Commun. 2016, 52, 9909. (10) (a) Zhao, B.; Liu, B.; Peng, R. Q.; Zhang, K.; Lim, K. A.; Luo, J.; Shao, J.; Ho, P. K. H.; Chi, C.; Wu, J. Chem. Mater. 2010, 22, 435. (b) Haneline, M. R.; Tsunoda, M.; Gabbai, F. P. J. Am. Chem. Soc. 2002, 124, 3737. (11) (a) Snape, T. J. Chem. Soc. Rev. 2007, 36, 1823. (b) Wang, B.; Tu, Y. Q. Acc. Chem. Res. 2011, 44, 1207. (12) Zaitsev, V. G.; Shabashov, D.; Daugulis, O. J. Am. Chem. Soc. 2005, 127, 13154.
E
DOI: 10.1021/acs.orglett.8b03511 Org. Lett. XXXX, XXX, XXX−XXX
