Revisiting Furodiindolines: One-Pot Synthesis of Furodiindolines

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Revisiting Furodiindolines: One-Pot Synthesis of Furodiindolines Using Indole 2,3-Epoxide Surrogates and Their Synthetic Applications Takumi Abe,* Sakura Aoyama, Masami Ohmura, Masato Taniguchi, and Koji Yamada* Faculty of Pharmaceutical Sciences, Health Sciences University of Hokkaido, Ishikari-tobetsu, Hokkaido 0610293, Japan Org. Lett. Downloaded from pubs.acs.org by UNIV AUTONOMA DE COAHUILA on 04/18/19. For personal use only.

S Supporting Information *

ABSTRACT: Furodiindolines have emerged as versatile intermediates in various transformations, which are easily obtained from indole 2,3-epoxide surrogates via a one-pot procedure and allowed access to heterocyclic compounds with structural diversity and complexity. Four types of transformations from the furodiindolines have been achieved: (i) dehydrative rearrangement to afford 2,3′biindoles, (ii) hydrolysis/cyclization to give 3,4-disubstituted quinolines, (iii) ring-opening/cyclization to give pyrroloindolines, and (iv) aminal cleavage to give a 3,3-disubstituted 2-oxindole.

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have not been reported in the literature except for Overman’s pioneering reports on the total synthesis of (−)-calycanthidine (Scheme 1a).14 Multiple steps are necessary to access the furodiindolines, and this may be one of the reasons for them being a missing substrate to date. Therefore, the development of a concise synthetic method and the investigation of their reactivity is waiting to be carried out. As part of our continuing work on the synthesis of indole alkaloids,15 we have previously reported the umpolung reactivity of 2-hydroxyindoline-3-triethylammonium bromides (HITABs, 1), affording valuable substituted indolines and indoles.16 For example, the reaction of HITAB with 2substituted indoles gives rise to 3,3′-biindole via a 3-indolyl-2hydroxyindoline intermediate (Scheme 1b).16a While extending the synthetic utility of this umpolung reactivity,17 we preliminary found that the reaction of HITAB with skatole afforded 2,3′-bisindole, which could be rationalized by the generation of a furodiindoline intermediate. Furodiindolines are expected to be potentially valuable synthetic intermediates due to their double hemiaminal moiety, which undergoes further transformations to afford various heterocycles with structural diversity and complexity. Therefore, we next chose to investigate the concise synthesis of furodiindolines using trifunctional HITABs and indoles, primarily because of the lack of complementary protocol for accessing this type of furodiindolination. Herein, we report the results of these efforts (Scheme 1c).

uroindolines are the core structures of various biologically important natural products (Figure 1).1 For example,

Figure 1. Selected furoindoline alkaloid, diazonamide A.

diazonamide A,2 which was isolated from the colonial marine ascidian Diazona angulate by Fenical and co-workers in 1991,2a shows potent antimitotic activity against a diverse range of human cancer cell lines. In 2007, Wang and Harran determined the active site of diazonamide A was ornithine δamino-transferase (OAT) and was implicated as a new anticancer reagents.2b Hence, furoindolines have attracted substantial interest from the organic synthetic community. Consequently, the chemistry of the furoindolines has witnessed an explosive resurgence1 because of the availability of a concise method for their preparation mediated by metal complexes such as Fe,3 Ag,4 Pd,5 and Cu.6 Furthermore, metal-free conditions have also been developed, including NIS-,7 hypervalent iodine(III)-,8 electrochemical-,9 and Bronsted acid-,10 Lewis acid-,11 radical-,12 and organocatalyst-promoted13 transformations. Even though furoindolines have been employed in organic synthesis over the past decade, surprisingly, furodiindolines © XXXX American Chemical Society

Received: March 28, 2019

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DOI: 10.1021/acs.orglett.9b01108 Org. Lett. XXXX, XXX, XXX−XXX

Letter

Organic Letters Scheme 2. Synthesis of Furodiindolines 3 and 4a,b

Scheme 1. Previous Works on Furodiindolines

We first evaluated the reaction of the HITABs 1a and skatole 2a in AcOEt under reflux conditions (Scheme 2). Only heating can efficiently promote the umpolung reaction and afforded furodiindolines transoid-3aa (52% yield) and cisoid4aa (38% yield) with poor regioselectivity. Fortunately, these furodiindolines exhibited good levels of stability. HITABs with an electron-donating or electron-withdrawing substituent at the 5-position of the indole ring can participate in the reaction to give the corresponding furodiindolines (3ba, 4ba, 3ca, and 4ca) with poor regioselectivities. Under the same conditions, the reaction of 2,3-dimethylindole (2b) generated targets (3ab, 3bb, 3cb, 4ab, 4bb, and 4cb) in a regioselective manner (transoid/cisoid = 2.1−3.6:1). We then investigated several indoles to improve the regioselectivity. Gratifyingly, the almost complete regioselectivity was observed in the case of the reaction of 1 with tetrahydrocarbazole (2c) because of the higher steric repulsions (3ac, 3bc, 3cc, and 4ac). The method also provided access to systems with additional functional groups on the side chain. Although the reaction with indoleacetic acid derivative 2d provides a poor yield with no regioselectivity, indole ethanol derivative 2e afforded target compounds (3ae and 4ae) in good yields. It was notable that the more complex substrate 2f was converted into furodiindoline 3af in 72% yield with complete regioselectivity. On the 1.0 mmol scale, 3af was also isolated in 66% yield. Thus, this reaction constitutes a highly regioselective furodiindolinization of 2,3-disubstituted indoles in addition to serving as an efficient and one-pot transformation without requiring a multistep procedures.14 HITABs are trifunctional indole reagents (Scheme 1c), which is presumably key to its achievement. To the best of our knowledge, this is the first time that the formation of a furodiindoline has been realized in only one chemical transformation. To demonstrate their synthetic potential, we explored the conversion of furodiindolines into 2,3′-biindoles. As shown in

a

1 (0.5 mmol), 2 (1 mmol), AcOEt (5 mL). bIsolated yields. c5 equiv of skatole (2a) was used. d2 equiv of Et3N was added. e5 equiv of 2e was used. fUsing AcOEt−DMF (v/v = 1/1, 40 mL) instead of AcOEt (5 mL). g1 (1.0 mmol), 2 (2 mmol), AcOEt-DMF (v/v = 1/1, 80 mL).

Scheme 3, the use of TsOH in toluene under reflux conditions promoted the formation of 5 or 6 in good yield over two steps from the HITABs. Notably, both transoid-3aa and cisoid-4aa B

DOI: 10.1021/acs.orglett.9b01108 Org. Lett. XXXX, XXX, XXX−XXX

Letter

Organic Letters

The furodiindolines accessed in this investigation have double hemiaminal moiety that can be modified further (Scheme 6). For example, compound 3aa was treated with

Scheme 3. Synthesis of 2,3′-Biindoles

Scheme 6. Synthesis of 3,4-Disubstituted Quinolines

are applicable to this transformation. Thus, it is not necessary to separate transoid-3aa and cisoid-4aa prior to this reaction. After intensive investigations, we realized a concise transformation of 2,3′-biindole from HITABs in a one-pot manner (Scheme 4). Scheme 4. Improved Synthesis of 2,3′-Biindoles NaOH at 50 °C for 10 h to furnish 3,4-disubstituted quinolines19b 12a and 12b in 50% and 25% yields, respectively (Scheme 6). Quinoline 12b was converted into methyl neocryptolepine (17).19 The formation of pyrroloindolines are also achieved by twostep procedures (Scheme 7);20 when 1a was treated with tryptamine 18a, the putative intermediate 20 underwent a smooth reaction upon the addition of TsOH to deliver the desired pyrroloindoline 19 in 66% yield as a single diastereomer. In addition, the reaction ran with tryptophan Scheme 7. Synthesis of Pyrroloindoline Due to the intriguing structural features of 2,3′-biindoles, we thought to explore its further synthetic applications toward the synthesis of indolo[3,2-a]carbazole alkaloids (Scheme 5).18 Scheme 5. Synthesis of Indolo[3,2-a]carbazole

The acetyl group in 6 was first removed to afford 9 in 68% yield. Then, under IBX−DMSO conditions, primary alcohol 9 was oxidized into aldehyde 10. A Mannich-type cyclization of 10 with dimethylamine furnished indolo[3,2-a]carbazole 11, which is the core structure of racemosine B.18c C

DOI: 10.1021/acs.orglett.9b01108 Org. Lett. XXXX, XXX, XXX−XXX

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Organic Letters Notes

18b, and the corresponding 23a and 23b were obtained in 21% yield and 11% yield, respectively. The untapped furodiindoline chemistry can be used to afford challenging 3,3′-disubstituted 2-oxindole21d,e common to synthetic intermediate of hexahydro[2,3-b]indole diketopiperadine alkaloids (Scheme 8).21 We performed many

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was financially supported by JSPS KAKENHI Grant No. 16K18849 (T.A.) in Grant-in-Aid for Young Scientists (B).

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Scheme 8. Synthesis of 3,3′-Disubstituted 2-Oxindole

experiments to selectively functionalize the aminal moiety of 3af. During our studies, the optimized conditions (TsOH, toluene, reflux) afforded to 3,3-disubstituted 2-oxindole 24. The improved procedure in Scheme 4 could also give 24 without purification of 3af. Enantiomer 24 is a core framework of chiral diketopiperadine alkaloids.21d−f The heterocycles obtained in this study by our method are core structures in many natural products.22 Therefore, we anticipate that the untapped chemistry described herein will find broader utility in synthetic communities. In summary, furodiindolines have emerged as versatile intermediates in various transformations, which are easily obtained from HITABs via a one-pot procedure and allowed access to heterocyclic compounds with structural diversity and complexity. The unprecedented reactivity of “old and new” furodiindolines is expected to open a new avenue for discovering novel transformations and divergent total synthesis using a common intermediate.22

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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.9b01108. Synthesis procedures and spectral and characterization data, including 1H and 13C NMR spectra (PDF)

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REFERENCES

(1) For reviews, see: (a) Lachia, M.; Moody, C. Nat. Prod. Rep. 2008, 25, 227. (b) Ito, Y.; Ueda, M.; Miyata, O. Heterocycles 2014, 89, 2029. (c) Roche, S. P.; Tendoung, J.-J. Y.; Tréguier, B. Tetrahedron 2015, 71, 3549. (d) Denizot, N.; Tomakinian, T.; Beaud, R.; Kouklovsky, C.; Vincent, G. Tetrahedron Lett. 2015, 56, 4413. (2) (a) Lindquist, N.; Fenical, W.; Van Duyne, G. D.; Clardy, J. J. Am. Chem. Soc. 1991, 113, 2303. (b) Li, J.; Burgett, A. W.; Esser, L.; Amezcua, C.; Harran, P. G. Angew. Chem., Int. Ed. 2001, 40, 4770. (c) Wang, G.; Shang, L.; Burgett, A. W. G.; Harran, P. G.; Wang, X. Proc. Natl. Acad. Sci. U. S. A. 2007, 104, 2068. (3) For Fe-mediated reactions, see: (a) Beaud, R.; Guillot, R.; Kouklovsky, C.; Vincent, G. Angew. Chem., Int. Ed. 2012, 51, 12546. (b) Tomakinian, T.; Guillot, R.; Kouklovsky, C.; Vincent, G. Angew. Chem., Int. Ed. 2014, 53, 11881. (c) Marques, A.-S.; Coeffard, V.; Chataigner, I.; Vincent, G.; Moreau, X. Org. Lett. 2016, 18, 5296. (d) Ye, J.; Lin, Y.; Liu, Q.; Xu, D.; Wu, F.; Liu, B.; Gao, Y.; Chen, H. Org. Lett. 2018, 20, 5457. (4) For Ag-mediated reactions, see: (a) Lachkar, D.; Denizot, N.; Bernadat, G.; Ahamada, K.; Beniddir, M. A.; Dumontet, V.; Gallard, J.-F.; Guillot, R.; Leblanc, K.; N’nang, E. O.; Turpin, V.; Kouklovsky, C.; Poupon, E.; Evanno, L.; Vincent, G. Nat. Chem. 2017, 9, 793. (b) Denizot, N.; Lachkar, D.; Kouklovsky, C.; Evanno, L.; Vincent, G. Synthesis 2018, 50, 4229. (5) For Pd-catalyzed reactions, see: (a) Boominathan, S. S. K.; Wang, J.-J. Chem. - Eur. J. 2015, 21, 17044. (b) Bizet, V.; BorrajoCalleja, G. M.; Besnard, C.; Mazet, C. ACS Catal. 2016, 6, 7183. (c) Borrajo-Calleja, G. M.; Bizet, V.; Besnard, C.; Mazet, C. Organometallics 2017, 36, 3553. (6) For Cu-mediated reactions, see: (a) Liu, C.; Zhang, W.; Dai, L.X.; You, S.-L. Org. Lett. 2012, 14, 4525. (b) Liu, C.; Zhang, W.; Dai, L.-X.; You, S.-L. Chem. - Asian J. 2014, 9, 2113. (c) Wu, S.-Y.; Chen, W.-L.; Ma, X.-P.; Liang, C.; Su, G.-F.; Mo, D.-L. Adv. Synth. Catal. 2019, 361, 965. (7) For NIS- or NFSI-mediated reactions, see: (a) Lozano, O.; Blessley, G.; del Campo, T. M.; Thompson, A. L.; Giffredi, G. T.; Bettati, M.; Walker, M.; Borman, R.; Gouverneur, V. Angew. Chem., Int. Ed. 2011, 50, 8105. (b) Liu, H.; Jiang, G.; Pan, X.; Wan, X.; Lai, Y.; Ma, D.; Xie, W. Org. Lett. 2014, 16, 1908. (c) Denizot, N.; Pouilhes, A.; Cucca, M.; Beaud, R.; Guillot, R.; Kouklovsky, C.; Vincent, G. Org. Lett. 2014, 16, 5752. (d) Tomakinian, T.; Hamdan, H. A.; Denizot, N.; Guillot, R.; Baltaze, J.-P.; Kouklovsky, C.; Vincent, G. Eur. J. Org. Chem. 2017, 2017, 2757. (e) Denizot, N.; Guillot, R.; Kouklovsky, C.; Vincent, G. Synthesis 2018, 50, 4823. (8) For iodine-mediated reactions, see: (a) Burgett, A. W. G.; Li, Q.; Wei, Q.; Harran, P. G. Angew. Chem., Int. Ed. 2003, 42, 4961. (b) Chan, C.; Li, C.; Zhang, F.; Danishefsky, S. J. Tetrahedron Lett. 2006, 47, 4839. (c) Nicolaou, K. C.; Majumder, U.; Roche, S. P.; Chen, D. Y.-K. Angew. Chem., Int. Ed. 2007, 46, 4715. (d) Nicolaou, K. C.; Dalby, S. M.; Li, S.; Suzuki, T.; Chen, D. Y.-K. Angew. Chem., Int. Ed. 2009, 48, 7616. (e) Zhao, J.-C.; Yu, S.-M.; Liu, Y.; Yao, Z.-J. Org. Lett. 2013, 15, 4300. (f) Zhao, J.-C.; Yu, S.-M.; Qiu, H.-B.; Yao, Z.-J. Tetrahedron 2014, 70, 3197. (g) Tomakinian, T.; Kouklovsky, C.; Vincent, G. Synlett 2015, 26, 1269. (h) Deruer, E.; Canesi, S. Org. Biomol. Chem. 2017, 15, 3736. (9) For a related reaction using electrochemistry, see: Liu, K.; Tang, S.; Huang, P.; Lei, A. Nat. Commun. 2017, 8, 775. (10) For Brønsted acid mediated reactions, see: (a) Boal, B. W.; Schammel, A. W.; Garg, N. K. Org. Lett. 2009, 11, 3458. (b) Zu, L.; Boal, B. W.; Garg, N. K. J. Am. Chem. Soc. 2011, 133, 8877. (c) Smith,

AUTHOR INFORMATION

Corresponding Authors

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

Takumi Abe: 0000-0003-1729-1097 D

DOI: 10.1021/acs.orglett.9b01108 Org. Lett. XXXX, XXX, XXX−XXX

Letter

Organic Letters J. M.; Moreno, J.; Boal, B. W.; Garg, N. K. J. Am. Chem. Soc. 2014, 136, 4504. (d) Liao, L.; Shu, C.; Zhang, M.; Liao, Y.; Hu, X.; Zhang, Y.; Wu, Z.; Yuan, W.; Zhang, X. Angew. Chem., Int. Ed. 2014, 53, 10471. (e) Chai, Z.; Chen, J.-N.; Liu, Z.; Li, X.-F.; Yang, P.-J.; Hu, J.P.; Yang, G. Org. Biomol. Chem. 2016, 14, 1024. (f) Tomakinian, T.; Guillot, R.; Kouklovsky, C.; Vincent, G. Chem. Commun. 2016, 52, 5443. (g) Simmons, B. J.; Hoffmann, M.; Champagne, P. A.; Picazo, E.; Yamakawa, K.; Morrill, L. A.; Houk, K. N.; Garg, N. K. J. Am. Chem. Soc. 2017, 139, 14833. (h) Liu, Q.-J.; Zhu, J.; Song, X.-Y.; Wang, L.; Wang, S. R.; Tang, Y. Angew. Chem. 2018, 130, 3872. (11) For Lewis acid mediated reactions, see: (a) Tian, W.; Chennamaneni, L. R.; Suzuki, T.; Chen, D. Y.-K. Eur. J. Org. Chem. 2011, 2011, 1027. (b) Hajra, S.; Maity, S.; Roy, S. Adv. Synth. Catal. 2016, 358, 2300. (12) For a related reaction via radicals, see: Cheng, B.; Zu, B.; Li, Y.; Zhai, S.; Xu, W.; Li, Y.; Zhai, H. Adv. Synth. Catal. 2018, 360, 474. (13) For examples of organocatalysis, see: (a) Austin, J. F.; Kim, S.G.; Sinz, C.-J.; Xiao, W.-J.; MacMillan, D. W. C. Proc. Natl. Acad. Sci. U. S. A. 2004, 101, 5482. (b) Knowles, R. R.; Carpenter, J.; Blakey, S. B.; Kayano, A.; Mangion, I. K.; Sinz, C. J.; MacMillan, D. W. C. Chem. Sci. 2011, 2, 308. (14) For Overman’s elegant works, see: (a) Link, J. T.; Overman, L. E. J. Am. Chem. Soc. 1996, 118, 8166. (b) Overman, L. E.; Paone, D. V.; Stearns, B. A. J. Am. Chem. Soc. 1999, 121, 7702. (c) Overman, L. E.; Peterson, E. A. Angew. Chem., Int. Ed. 2003, 42, 2525. (d) Overman, L. E.; Peterson, E. A. Tetrahedron 2003, 59, 6905. (15) (a) Abe, T.; Ikeda, T.; Yanada, R.; Ishikura, M. Org. Lett. 2011, 13, 3356. (b) Abe, T.; Komatsu, H.; Ikeda, T.; Hatae, N.; Toyota, E.; Ishikura, M. Heterocycles 2012, 86, 505. (c) Abe, T.; Ikeda, T.; Yanada, R.; Ishikura, M. Eur. J. Org. Chem. 2012, 2012, 5018. (d) Abe, T.; Ikeda, T.; Yanada, R.; Ishikura, M. Org. Lett. 2013, 15, 3622. (e) Abe, T.; Ikeda, T.; Itoh, T.; Hatae, N.; Toyota, E.; Ishikura, M. Heterocycles 2014, 88, 187. (f) Abe, T.; Itoh, T.; Hibino, S.; Choshi, T.; Ishikura, M. Tetrahedron Lett. 2014, 55, 5268. (g) Abe, T.; Ishikura, M. Heterocycles 2015, 90, 673. (h) Itoh, T.; Abe, T.; Nakamura, S.; Ishikura, M. Heterocycles 2015, 91, 1423. (i) Itoh, T.; Abe, T.; Choshi, T.; Nishiyama, T.; Yanada, R.; Ishikura, M. Eur. J. Org. Chem. 2016, 2016, 2290. (j) Abe, T.; Yamada, K. Org. Lett. 2016, 18, 6504. (k) Abe, T.; Yamada, K. J. Nat. Prod. 2017, 80, 241. (l) Abe, T.; Kida, K.; Yamada, K. Chem. Commun. 2017, 53, 4362. (m) Abe, T.; Haruyama, T.; Yamada, K. Synthesis 2017, 49, 4141. (n) Abe, T.; Takahashi, Y.; Matsubara, Y.; Yamada, K. Org. Chem. Front. 2017, 4, 2124. (o) Abe, T.; Terasaki, M. Helv. Chim. Acta 2018, 101, No. e1700284. (p) Abe, T. Heterocycles 2018, 96, 490. (q) Abe, T.; Morita, T.; Yamada, K. Heterocycles 2018, 97, 141. (r) Abe, T.; Kosaka, Y.; Asano, M.; Harasawa, N.; Mishina, A.; Nagasue, M.; Sugimoto, Y.; Katakawa, K.; Sueki, S.; Anada, M.; Yamada, K. Org. Lett. 2019, 21, 826. (16) For our trifunctional indole reagents, see: (a) Abe, T.; Suzuki, T.; Anada, M.; Matsunaga, S.; Yamada, K. Org. Lett. 2017, 19, 4275. (b) Abe, T.; Yamada, K. Org. Lett. 2018, 20, 1469. (c) Abe, T.; Shimizu, H.; Takada, S.; Tanaka, T.; Yoshikawa, M.; Yamada, K. Org. Lett. 2018, 20, 1589. (d) Abe, T.; Satake, S.; Yamada, K. Heterocycles 2019, 99, 379. (17) For a review, see: Bandini, M. Org. Biomol. Chem. 2013, 11, 5206. (18) (a) Meragelman, K. M.; West, L. M.; Northcote, P. T.; Pannell, L. K.; McKee, T. C.; Boyd, M. R. J. Org. Chem. 2002, 67, 6671. (b) Liu, D.-Q.; Mao, S.-C.; Zhang, H.-Y.; Yu, X.-Q.; Feng, M.-T.; Wang, B.; Feng, L.-H.; Guo, Y.-W. Fitoterapia 2013, 91, 15. (c) Russell, F.; Harmody, D.; McCarthy, P. J.; Pomponi, S. A.; Wright, A. E. J. Nat. Prod. 2013, 76, 1989. (19) (a) Cimanga, K.; DeBruyne, T.; Pieters, L.; Claeys, M.; Vlietinck, A. Tetrahedron Lett. 1996, 37, 1703. (b) Sharaf, M. H. M.; Schiff, P. L.; Tackie, A. N.; Phoebe, C. H.; Martin, G. E. J. Heterocycl. Chem. 1996, 33, 239. (c) Vecchione, M. K.; Sun, A. X.; Seidel, D. Chem. Sci. 2011, 2, 2178. (20) For related sulfonium-mediated cross-coupling of tryptophans or tryptamines and indoles through cyclization/indolization in one

pot, see: (a) Tayu, M.; Higuchi, K.; Ishizaki, T.; Kawasaki, T. Org. Lett. 2014, 16, 3613. (b) Tayu, M.; Ishizaki, T.; Higuchi, K.; Kawasaki, T. Org. Biomol. Chem. 2015, 13, 3863. (c) Tayu, M.; Suzuki, Y.; Higuchi, K.; Kawasaki, T. Synlett 2016, 27, 941. (d) Tayu, M.; Hui, Y.; Takeda, S.; Higuchi, K.; Saito, N.; Kawasaki, T. Org. Lett. 2017, 19, 6582. (21) (a) Usami, Y.; Yamaguchi, J.; Numata, A. Heterocycles 2004, 63, 1123. (b) Feng, Y.; Blunt, J. W.; Cole, A. L. J.; Munro, M. H. G. J. Nat. Prod. 2004, 67, 2090. (c) Dong, J.-Y.; He, H.-P.; Shen, Y.-M.; Zhang, K.-Q. J. Nat. Prod. 2005, 68, 1510. (d) Hodges, T. R.; Benjamin, N. M.; Martin, S. F. Org. Lett. 2017, 19, 2254. (e) Hodges, T. R.; Benjamin, N.; Martin, S. F. Tetrahedron 2018, 74, 3329. (f) DeLorbe, J. E.; Horne, D.; Jove, R.; Mennen, S. M.; Nam, D.; Zhang, F.; Overman, L. E. J. Am. Chem. Soc. 2013, 135, 4117. (22) For a useful review, see: Li, Z.; Chen, Z.; Zhang, X.; Jia, Y. Chem. Rev. 2018, 118, 3752.

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DOI: 10.1021/acs.orglett.9b01108 Org. Lett. XXXX, XXX, XXX−XXX