Letter pubs.acs.org/OrgLett
Cite This: Org. Lett. XXXX, XXX, XXX−XXX
A [4 + 3] Annulation Reaction of aza‑o‑Quinone Methides with Arylcarbohydrazonoyl Chlorides for Synthesis of 2,3Dihydro‑1H‑benzo[e][1,2,4]triazepines Zhenyan Guo, Hao Jia, Honglei Liu, Qijun Wang, Jiaxing Huang, and Hongchao Guo* Department of Applied Chemistry, China Agricultural University, Beijing 100193, P. R. China S Supporting Information *
ABSTRACT: An unprecedented [4 + 3] annulation reaction of aza-ortho-quinone methides with arylcarbohydrazonoyl chlorides has been achieved under mild conditions. The annulation underwent a sequential conjugate addition/intramolecular annulation/rearrangement, providing a useful method for the synthesis of biologically interesting 2,3-dihydro-1H-benzo[e][1,2,4]triazepine.
N
Scheme 1. Cycloaddition Reactions Involving aza-orthoQuinone Methides (ao-QMs)
itrogen-containing seven-membered heterocycles are widely found in natural products and artificial drugs.1 As one type of the seven-membered heterocyclic compounds, triazepines display a variety of practical pharmacological activities and have widely been used as anticancer agents, antibiotics, antiviral drugs, psychotropic drugs, antisecretagogues, CCK2 antagonists, analgesics, and antiinflammatory drugs.2 Among various triazepines, 1,2,4-benzotriazepines were nonpeptide parathyroid hormone-1 receptor (PTH1R) antagonists and have been used in the treatment of malignancyassociated hypercalcaemia (MAHCa).3 It is of great value to explore practical synthetic methods of 1,2,4-benzotriazepines. ortho-Quinone methides (o-QMs) and aza-ortho-quinone methides (ao-QMs) are known to be very reactive intermediates that have been utilized in both biological processes and organic synthesis for decades.4 By using stabilized or in situ generated o-QMs as an oxa-diene, numerous [4 + 1],5 [4 + 2],6 [4 + 3],7 and [4 + 4]8 cycloadditions have been established to furnish synthesis of various heterocyclic compounds. In contrast, ao-QMs have mainly been used in [4 + 2] cycloaddition reactions with olefins, alkynes, and other reaction substrates bearing a carbon−nitrogen double bond9 or a carbon−sulfur double bond (Scheme 1a).10 In comparison with [4 + 2] cycloadditions, other types of cycloaddition reactions involving aoQMs are quite limited. One of these limited examples was the [4 + 1]11 annulation reaction of ao-QMs generated in situ with sulfur ylides, affording indole products.12 Other examples focused on [4 + 3] cycloaddition reactions. In 2015, the [4 + 3] cycloaddition between ao-QMs and MBH adducts derived from isatins was achieved to give a challenging azaspirocycloheptane oxindole scaffold.13 The [4 + 3] cycloaddition reaction of in situ generated ao-QMs with C,N-cyclic azomethine imines led to 1,2,4-triazepine derivatives.14 NHC-catalyzed asymmetric [4 + 3] annulation of isatin-derived enals with in situ generated aza-o-quinone methides afforded spirobenzazepinones.15As an important type of 1,3-dipoles,16 nitrilimines generated in situ © XXXX American Chemical Society
from the hydrazonyl halides have been widely utilized in various cycloaddition reactions. They often react with olefins or alkynes to form heterocyclic compounds such as pyrazolines and pyrazoles through the [3 + 2] cycloaddition.17 Other types of cycloaddition reactions of nitrilimines have received little attention. On the basis of the above-mentioned [4 + 3] cycloadditions involving ao-QMs13−15,18 and our previous work on cycloaddition reactions,19 we envisioned that when ao-QMs meet with nitrilimines, a new [4 + 3] annulation for synthesis of seven-membered heterocyclic compounds might be accomplished to furnish 4,5-dihydro-1H-benzo[e][1,2,4]triazepine (Scheme 1b). However, an unexpected [4 + 3] annulation of Received: March 28, 2018
A
DOI: 10.1021/acs.orglett.8b00990 Org. Lett. XXXX, XXX, XXX−XXX
Letter
Organic Letters
aggregation of the ao-QM at lower temperature, the reaction was carried out at −40 °C, however, the yield was not improved (entry 11). In contrast, increasing the temperature to −20 °C slightly improved the yield to 76% (entry 12), but further increasing the reaction temperature to −10 and 0 °C resulted in a remarkable side reaction and thus deteriorated the yields (entries 13−14). According to the observation that the silica could promote conversion of the intermediate 3 to the product 4aa, the experimental procedure was modified. After the reaction mixture of ao-QMs precursor 1a and the substrate 2a was stirred in dichloromethane at −30 °C for 36 h, the silica gel was added into the flask to promote conversion of the intermediate to the desired product and the resulting mixture continued to be stirred for 12 h to give the product in 78% yield (entry 15). With the optimal reaction conditions identified, the scope of the substrates was then investigated. As shown in Table 2,
aza-ortho-quinone methides with arylcarbohydrazonoyl chlorides was observed, leading to 2,3-dihydro-1H-benzo[e][1,2,4]triazepine (Scheme 1b). Herein, we report this [4 + 3] annulation reaction for the synthesis of 2,3-dihydro-1Hbenzo[e][1,2,4]triazepines (Scheme 1b). In the initial study, the reaction of ao-QMs precursor 1a with N-phenylbenzohydrazonoyl chloride 2a was chosen as the model reaction for screening the reaction conditions (Table 1). Table 1. Optimization of Reaction Conditionsa
entry
base
solvent
t (°C)
yield (%)b
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15d
DIPEA KOAc NaOAc K2CO3 Cs2CO3 Na2CO3 Na2CO3 Na2CO3 Na2CO3 Na2CO3 Na2CO3 Na2CO3 Na2CO3 Na2CO3 Na2CO3
CH2Cl2 CH2Cl2 CH2Cl2 CH2Cl2 CH2Cl2 CH2Cl2 DCE 1,4-dioxane toluene THF CH2Cl2 CH2Cl2 CH2Cl2 CH2Cl2 CH2Cl2
−30 −30 −30 −30 −30 −30 −30 −30 −30 −30 −40 −20 −10 0 −20
NRc 57 10 27 54 72 63 42 40 29 72 76 65 64 78
Table 2. Scope of Arylcarbohydrazonoyl Chlorides 2a
a
Unless otherwise noted, reactions were conducted with 1a (0.1 mmol), 2a (0.12 mmol), and base (0.2 mmol) in solvent (2 mL) for 36 h. bIsolated yield. cNo reaction. dAfter the reaction mixture was stirred for 36 h, 500 mg of silica gel were added and the resulting mixture was stirred for 12 h at rt.
Since the base plays a key role in the reaction of ao-QMs, we first examined two bases such as diisopropylethylamine (DIPEA) and KOAc. In the presence of organic base DIPEA, the reaction did not work and no product was observed (Table 1, entry 1). With the use of KOAc as the base, the reaction of ao-QMs precursor 1a with N-phenylbenzohydrazonoyl chloride 2a was performed in dichloromethane at −30 °C for 36 h. During the reaction process, two products were observed on TLC. Moreover, the major product could convert into the minor one during purification through flash column. It indicated that the silica gel promoted the conversion of the intermediate to the final product. Through NMR data and the X-ray crystallographic analysis, the intermediate was identified as the benzohydrazonoyl chloride 3 (CCDC 1832290). The product was determined as a 2,3-dihydro-1H-benzo[e][1,2,4]triazepine derivative 4aa (CCDC 1587333), which is an unexpected [4 + 3] annulation product and was isolated in 57% yield by flash column chromatography (entry 2). Different inorganic bases such as acetate and carbonate bases were next screened to improve the yield (entries 3−6). To our delight, the yield of the product 4aa was increased to 72% with the use of Na2CO3 as the base (entry 6). The impact of the solvent was also examined. Compared with dichloromethane, 1,2-dichloroethane (DCE), 1,4-dioxane, toluene, and tetrahydrofuran (THF) led to a decrease in yields (entries 7−10). Considering that the yield might be increased by suppressing the self-
entry
R1
R2, R3
4
yield (%)b
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
H (1a) H (1a) H (1a) H (1a) H (1a) H (1a) H (1a) H (1a) H (1a) H (1a) H (1a) H (1a) H (1a) H (1a) H (1a) H (1a) 4-Me (1d) 4-Me (1d)
Ph, Ph (2a) 2-FC6H4, Ph (2b) 3-FC6H4, Ph (2c) 4-FC6H4, Ph (2d) 2-BrC6H4, Ph (2e) 3-BrC6H4, Ph (2f) 4-BrC6H4, Ph (2g) 3-ClC6H4, Ph (2h) 4-MeC6H4, Ph (2i) 4-MeOC6H4, Ph (2j) 1-naphthyl, Ph (2k) 2-naphthyl, Ph (2l) Ph, 4-BrC6H4 (2m) Ph, 4-ClC6H4 (2n) Ph, 3-FC6H4 (2o) Ph, 4-MeC6H4 (2p) 4-MeC6H4, Ph (2i) Ph, 4-MeC6H4 (2p)
4aa 4ab 4ac 4ad 4ae 4af 4ag 4ah 4ai 4aj 4ak 4al 4am 4an 4ao 4ap 4di 4dp
78 52 64 70 59 55 62 54 71 70 74 71 55 53 53 72 53 76
a Unless otherwise noted, reactions were performed with 1a (0.1 mmol), 2a (0.12 mmol), and Na2CO3 (0.2 mmol) in CH2Cl2 (2.0 mL) at −20 °C for 36 h, then 500 mg of silica gel were added, and the resulting mixture was stirred at rt for 12−36 h depending on TLC monitoring. bIsolated yield.
various arylcarbohydrazonoyl chlorides 2 having diverse electron-donating or -withdrawing groups at different positions of the benzene ring performed the reaction well to give the products 4 in moderate to high yields (52−78%) (entries 1− 10). In general, substrates with electron-donating groups on the benzene ring exhibited higher reactivity than those with electron-withdrawing groups (entries 9−10 vs 2−8). The substrates bearing substituents at the 4-position of the aryl showed relative higher reactivity than their corresponding analogues with substituents at the 2- or 3-position of the aryl as a result of the steric hindrance effect, leading to the corresponding products in a slightly higher yield (entries 4, 7, 9−10). In addition, arylcarbohydrazonoyl chlorides with B
DOI: 10.1021/acs.orglett.8b00990 Org. Lett. XXXX, XXX, XXX−XXX
Letter
Organic Letters different R3 substituents could also be tolerated (entries 13− 16). The reaction of methyl-substituted ao-QMs and methylsubstituted arylcarbohydrazonoyl chlorides also underwent the reaction to give the corresponding products in moderate to high yields (entries 17−18). Next, we carried out an investigation on ao-QM precursors 1 (Table 3). A series of ao-QM bearing different R groups were
Scheme 2. Control Experiments
Table 3. Scope of ao-QM Precursors 1a
entry
R
4
yield (%)b
1 2c 3 4 5 6 7 8
H (1a) 6-Me (1b) 5-Me (1c) 4-Me (1d) 3-Me (1e) 5-F (1f) 3-F (1g) 3-Cl (1h)
4aa 4ba 4ca 4da 4ea 4fa 4ga 4ha
78 37 65 70 65 62 54 59
a
Unless otherwise noted, reactions were performed with 1a (0.1 mmol), 2a (0.12 mmol), and Na2CO3 (0.2 mmol) in CH2Cl2 (2.0 mL) at −20 °C for 36 h, and then 500 mg of silica gel were added, and the mixture was stirred at rt for 12−36 h. bIsolated yield. cThe reaction temperature was 25 °C.
Scheme 3. A Plausible Mechanism
compatible with the reaction. With the exception of 6-Mesubstituted ao-QM precursor (1b), other substrates carried out the annulation reaction to give the corresponding products 4 in moderate to good yields (Table 3, entries 1, 3−8). The electronic properties or position of the substituent on the benzene ring seems to have no significant effect on the reaction (entries 1, 3−8). The 6-Me-susbstitiued ao-QM precursor was not very reactive and only gave the product 4ba in 37%yield (entry 2). Delightedly, the reaction could be scaled up. Using 1 mmol of ao-QM precursor 1d as the substrate, the corresponding product 4da was obtained in 64% yield (see Supporting Information). In order to shed light on the reaction mechanism, some control experiments had been carried out (Scheme 2). The substrate 2g derived from 4-bromobenzoyl chloride reacted with ao-QMs to give the products 4ag (CCDC 1587334), in which 4-bromophenyl sits at the 5-position of the triazepine. On the other hand, the substrate 2m derived from (4bromophenyl)hydrazine reacted with ao-QMs to afford the corresponding product 4am (CCDC 1587335), in which 4bromophenyl sits at the 3-position of the triazepine. On the basis of the experimental results, as shown in Scheme 3, a plausible mechanism for the stepwise annulation reaction was proposed. The ao-QM A generated in situ from ao-QMs precursor 1a in the presence of Na2CO3 reacts with the substrate 2a through conjugate addition to produce an intermediate 3, which has been isolated and confirmed by its X-ray crystallographic data. In the presence of silica gel, the intermediate 3 performs deprotonation and isomerization to afford the intermediate B, which undergoes an intramolecular annulation to produce the intermediate C. Further rearrangement due to aromatization results in the product 4aa. The role of the silica gel in the conversion of the intermediate B to the
product 4aa has been explored. In the reaction process, acetic acid, benzoic acid, and p-toluene sulfonic acid were added instead of silica gel, respectively, leading to no remarkable conversion. It indicated that the protonic acid can prevent the isomerization of the intermediate 3. Furthermore, by replacing silica gel with anhydrous FeCl3 and MgSO4, the product was obtained in 57% and 64% yield, respectively (Scheme 2). On the basis of the above observations, on one hand, the silica gel’s function probably is increasing the contact surface of the intermediate 3 with solvent, thus making the further transformation more easy; on the other hand, the silica gel might activate the intermediates 3 and B. In conclusion, we have developed a useful method for synthesis of biologically significant 2,3-dihydro-1H-benzo[e][1,2,4]triazepine through the [4 + 3] annulation reaction between in situ generated aza-ortho-quinone methides and arylcarbohydrazonoyl chlorides with the use of Na2CO3 as the base in the presence of silica gel. The reaction underwent a sequential conjugate addition, intramolecular annulation, and rearrangement processes. The ao-QMs functioned as an C
DOI: 10.1021/acs.orglett.8b00990 Org. Lett. XXXX, XXX, XXX−XXX
Letter
Organic Letters
Klimochkin, Y. N. Tetrahedron 2012, 68, 5612. (f) Green, J. C.; Brown, E. R.; Pettus, T. R. R. Org. Lett. 2012, 14, 2929. (g) Hsiao, C. C.; Liao, H. H.; Rueping, M. Angew. Chem., Int. Ed. 2014, 53, 13258. (h) Lee, A.; Scheidt, K. A. Chem. Commun. 2015, 51, 3407. (i) El-Sepelgy, O.; Haseloff, S.; Alamsetti, S. K.; Schneider, C. Angew. Chem., Int. Ed. 2014, 53, 7923. (j) Hu, H.; Liu, Y.; Guo, J.; Lin, L.; Xu, Y.; Liu, X.; Feng, X. Chem. Commun. 2015, 51, 3835. (k) Alamsetti, S. K.; Spanka, M.; Schneider, C. Angew. Chem., Int. Ed. 2016, 55, 2392. (l) Deng, Y. H.; Chu, W. D.; Zhang, X. Z.; Yan, X.; Yu, K. Y.; Yang, L. L.; Huang, H.; Fan, C. A. J. Org. Chem. 2017, 82, 5433. (m) Chen, P.; Wang, K.; Guo, W.; Liu, X.; Liu, Y.; Li, C. Angew. Chem., Int. Ed. 2017, 56, 3689. (n) Tang, M.; Zhao, J. J.; Wu, Q.; Tu, M. S.; Shi, F. Synthesis 2017, 49, 2035. (o) Jian, H.; Liu, K.; Wang, W. H.; Li, Z. J.; Dai, B.; He, L. Tetrahedron Lett. 2017, 58, 1137. (p) Wang, Z.; Wang, T.; Yao, W.; Lu, Y. Org. Lett. 2017, 19, 4126. (q) Wu, B.; Yu, Z.; Gao, X.; Lan, Y.; Zhou, Y. G. Angew. Chem., Int. Ed. 2017, 56, 4006. (7) (a) Izquierdo, J.; Orue, A.; Scheidt, K. A. J. Am. Chem. Soc. 2013, 135, 10634. (b) Mei, G. J.; Zhu, Z. Q.; Zhao, J. J.; Bian, C. Y.; Chen, J.; Chen, R. W.; Shi, F. Chem. Commun. 2017, 53, 2768. (8) Samarakoon, T. B.; Hur, M. Y.; Kurtz, R. D.; Hanson, P. R. Org. Lett. 2010, 12, 2182. (9) (a) Muñnoz, G. G.; Madroñero, R. Chem. Ber. 1962, 95, 2182. (b) Cremonesi, G.; Croce, P. D.; Gallanti, M. Heterocycles 2010, 80, 2593. (10) (a) Steinhagen, H.; Corey, E. J. Angew. Chem., Int. Ed. 1999, 38, 1928. (b) Gromachevskaya, E. V.; Krapivin, G. D.; Kvitkovskii, F. V.; Shein, A. O.; Kul’nevich, V. G. Chem. Heterocycl. Compd. 2001, 37, 588. (c) Boal, B. W.; Schammel, A. W.; Garg, N. K. Org. Lett. 2009, 11, 3458. (d) Lee, A.; Younai, A.; Price, C. K.; Izquierdo, J.; Mishra, R. K.; Scheidt, K. A. J. Am. Chem. Soc. 2014, 136, 10589. (e) Mancini, A.; Chelini, A.; Di Capua, A.; Castelli, L.; Brogi, S.; Paolino, M.; Giuliani, G.; Cappelli, A.; Frosini, M.; Ricci, L. Eur. J. Med. Chem. 2017, 126, 614. (f) Saunthwal, R. K.; Patel, M.; Verma, A. K. Org. Lett. 2016, 18, 2200. (g) Saunthwal, R. K.; Patel, M.; Verma, A. K. J. Org. Chem. 2016, 81, 6563. (11) (a) Huang, H.; Yang, Y.; Zhang, X.; Zeng, W.; Liang, Y. Tetrahedron Lett. 2013, 54, 6049. (b) Yang, Q. Q.; Wang, Q.; An, J.; Chen, J. R.; Lu, L. Q.; Xiao, W. J. Chem. - Eur. J. 2013, 19, 8401. (c) Hovey, M. T.; Check, C. T.; Sipher, A. F.; Scheidt, K. A. Angew. Chem., Int. Ed. 2014, 53, 9603. (d) Sharma, H. A.; Hovey, M. T.; Scheidt, K. A. Chem. Commun. 2016, 52, 9283. (12) Yang, Q. Q.; Xiao, C.; Lu, L. Q.; An, J.; Tan, F.; Li, B. J.; Xiao, W. J. Angew. Chem., Int. Ed. 2012, 51, 9137. (13) Zhan, G.; Shi, M. L.; He, Q.; Du, W.; Chen, Y. C. Org. Lett. 2015, 17, 4750. (14) Chen, L.; Yang, G. M.; Wang, J.; Jia, Q. F.; Wei, J.; Du, Z. Y. RSC Adv. 2015, 5, 76696. (15) Wang, L.; Li, S.; Blumel, M.; Philipps, A. R.; Wang, A.; Puttreddy, R.; Rissanen, K.; Enders, D. Angew. Chem., Int. Ed. 2016, 55, 11110. (16) (a) Gothelf, K. V.; Jørgensen, K. A. Chem. Rev. 1998, 98, 863. (b) Pellissier, H. Tetrahedron 2007, 63, 3235. (c) Hashimoto, T.; Maruoka, K. Chem. Rev. 2015, 115, 5366. (d) Singh, M. S.; Chowdhury, S.; Koley, S. Tetrahedron 2016, 72, 1603. (17) For selected examples, see: (a) Meazza, G.; Zanardi, G. J. Fluorine Chem. 1994, 67, 183. (b) Yavari, I.; Khalili, G.; Mirzaei, A. Helv. Chim. Acta 2010, 93, 277. (c) Wang, G.; Liu, X.; Huang, T.; Kuang, Y.; Lin, L.; Feng, X. Org. Lett. 2013, 15, 76. (d) Liu, H.; Jia, H.; Wang, B.; Xiao, Y.; Guo, H. Org. Lett. 2017, 19, 4714. (18) Liu, J. Y.; Lu, H.; Li, C. G.; Liang, Y. M.; Xu, P. F. Synlett 2016, 27, 1287. (19) (a) Na, R.; Jing, C.; Xu, Q.; Jiang, H.; Wu, X.; Shi, J.; Zhong, J.; Wang, M.; Benitez, D.; Tkatchouk, E.; Goddard, W. A.; Guo, H.; Kwon, O. J. Am. Chem. Soc. 2011, 133, 13337. (b) Yu, H.; Zhang, L.; Li, Z.; Liu, H.; Wang, B.; Xiao, Y.; Guo, H. Tetrahedron 2014, 70, 340. (c) Yuan, C.; Liu, H.; Gao, Z.; Zhou, L.; Feng, Y.; Xiao, Y.; Guo, H. Org. Lett. 2015, 17, 26. (d) Liu, H.; Yuan, C.; Wu, Y.; Xiao, Y.; Guo, H. Org. Lett. 2015, 17, 4220. (e) Zhang, L.; Liu, H.; Qiao, G.; Hou, Z.; Liu, Y.; Xiao, Y.; Guo, H. J. Am. Chem. Soc. 2015, 137, 4316. (f) Yuan,
abnormal four-membered synthon to furnish [4 + 3] annulation.
■
ASSOCIATED CONTENT
* Supporting Information S
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.orglett.8b00990. Experimental procedure, characterization data, and NMR spectra (PDF) Accession Codes
CCDC 1587333−1587335 and 1832290 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 Author
*E-mail:
[email protected]. ORCID
Hongchao Guo: 0000-0002-7356-4283 Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS This work is supported by the NSFC (Nos. 21372256, 21572264) and the Program for Changjiang Scholars and Innovative Research Team Project IRT1042.
■
REFERENCES
(1) (a) Shu, X. Z.; Li, X.; Shu, D.; Huang, S.; Schienebeck, C. M.; Zhou, X.; Robichaux, P. J.; Tang, W. J. Am. Chem. Soc. 2012, 134, 5211. (b) Zhou, M. B.; Song, R. J.; Wang, C. Y.; Li, J. H. Angew. Chem., Int. Ed. 2013, 52, 10805. (c) Zhou, M. B.; Song, R. J.; Li, J. H. Angew. Chem., Int. Ed. 2014, 53, 4196. (2) (a) Spencer, J.; Gaffen, J.; Griffin, E.; Harper, E. A.; Linney, I. D.; Mcdonald, I. M.; Roberts, S. P.; Shaxted, M. E.; Adatia, T.; Bashall, A. Bioorg. Med. Chem. 2008, 16, 2974. (b) Kaur, K.; Talele, T. T. J. Mol. Graphics Modell. 2008, 27, 409. (c) Yang, W.; Yuan, C.; Liu, Y.; Mao, B.; Sun, Z.; Guo, H. J. Org. Chem. 2016, 81, 7597. (3) (a) Mcdonald, I. M.; Austin, C.; Buck, I. M.; Dunstone, D. J.; Gaffen, J.; Griffin, E.; Harper, E. A.; Hull, R. A.; Kalindjian, S. B.; Linney, I. D.; Low, C. M.; Patel, D.; Pether, M. J.; Raynor, M.; Roberts, S. P.; Shaxted, M. E.; Spencer, J.; Steel, K. I.; Sykes, D. A.; Wright, P. T.; Xun, W. J. Med. Chem. 2007, 50, 4789. (b) Elattar, K. M.; Abozeid, M. A.; Etman, H. A. Synth. Commun. 2016, 46, 93. (4) Jaworski, A. A.; Scheidt, K. A. J. Org. Chem. 2016, 81, 10145. (5) (a) Cadonà, L.; Croce, P. D. Synthesis 1976, 1976, 800. (b) Chen, M. W.; Cao, L. L.; Ye, Z. S.; Jiang, G. F.; Zhou, Y. G. Chem. Commun. 2013, 49, 1660. (c) Osyanin, V. A.; Osipov, D. V.; Klimochkin, Y. N. J. Org. Chem. 2013, 78, 5505. (d) Rodriguez, K. X.; Vail, J. D.; Ashfeld, B. L. Org. Lett. 2016, 18, 4514. (e) Meisinger, N.; Roiser, L.; Monkowius, U.; Himmelsbach, M.; Robiette, R.; Waser, M. Chem. - Eur. J. 2017, 23, 5137. (f) Lian, X. L.; Adili, A.; Liu, B.; Tao, Z. L.; Han, Z. Y. Org. Biomol. Chem. 2017, 15, 3670. (6) (a) von Strandtmann, M.; Cohen, M. P.; Shavel, J., Jr. Tetrahedron Lett. 1965, 6, 3103. (b) Breuer, E.; Melumad, D. Tetrahedron Lett. 1969, 10, 1875. (c) Katada, T.; Eguchi, S.; Esaki, T.; Sasaki, T. J. Chem. Soc., Perkin Trans. 1 1984, 1869. (d) Böhme, T. M.; Augelliszafran, C. E.; Hallak, H.; Pugsley, T.; Serpa, K.; Schwarz, R. D. J. Med. Chem. 2002, 45, 3094. (e) Osyanin, V. A.; Osipov, D. V.; D
DOI: 10.1021/acs.orglett.8b00990 Org. Lett. XXXX, XXX, XXX−XXX
Letter
Organic Letters C.; Zhou, L.; Xia, M.; Sun, Z.; Wang, D.; Guo, H. Org. Lett. 2016, 18, 5644. (g) Liu, H.; Liu, Y.; Yuan, C.; Wang, G.-P.; Zhu, S. F.; Wu, Y.; Wang, B.; Sun, Z.; Xiao, Y.; Zhou, Q.-L.; Guo, H. Org. Lett. 2016, 18, 1302. (h) Wang, C.; Gao, Z.; Zhou, L.; Yuan, C.; Sun, Z.; Xiao, Y.; Guo, H. Org. Lett. 2016, 18, 3418. (i) Zhou, L.; Yuan, C.; Zhang, C.; Zhang, L.; Gao, Z.; Wang, C.; Liu, H.; Wu, Y.; Guo, H. Adv. Synth. Catal. 2017, 359, 2316. (j) Jia, H.; Liu, H.; Guo, Z.; Huang, J.; Guo, H. Org. Lett. 2017, 19, 5236. (k) Wu, Y.; Yuan, C.; Wang, C.; Mao, B.; Jia, H.; Gao, X.; Liao, J.; Jiang, F.; Zhou, L.; Wang, Q.; Guo, H. Org. Lett. 2017, 19, 6268. (l) Yuan, C.; Wu, Y.; Wang, D.; Zhang, Z.; Wang, C.; Zhou, L.; Zhang, C.; Song, B. A.; Guo, H. Adv. Synth. Catal. 2018, 360, 652. (m) Zhou, L.; Yuan, C.; Zeng, Y.; Liu, H.; Wang, C.; Gao, X.; Wang, Q.; Zhang, C.; Guo, H. Chem. Sci. 2018, 9, 1831.
E
DOI: 10.1021/acs.orglett.8b00990 Org. Lett. XXXX, XXX, XXX−XXX
