Dinuclear Zinc-Catalyzed Asymmetric Tandem Reaction of α-Hydroxy

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Letter Cite This: Org. Lett. XXXX, XXX, XXX−XXX

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Dinuclear Zinc-Catalyzed Asymmetric Tandem Reaction of α‑Hydroxy-1-indanone: Access to Spiro[1-indanone-5,2′-γbutyrolactones] Meng-Meng Liu, Xiao-Chao Yang, Yuan-Zhao Hua,* Jun-Biao Chang,* and Min-Can Wang* College of Chemistry and Molecular Engineering, Zhengzhou University, 100 Science Avenue, Zhengzhou, Henan 450001, People’s Republic of China Downloaded via STOCKHOLM UNIV on August 29, 2019 at 00:38:13 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

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ABSTRACT: A highly efficient method for the enantioselective build of spiro[1-indanone-5,2′-γ-butyrolactones] has been developed through the tandem Michael/transesterification reaction of α-hydroxy-1-indanone and α,β-unsaturated esters. A broad range of spiro(1-indanone-butyrolacones) with contiguous stereocenters have been synthesized with excellent stereoselectivities (up to >20:1 dr, up to >99% ee) under the catalysis of dinuclear zinc complex. Moreover, the reaction can be run on a gram scale without affecting its stereoselectivities. A possible mechanism is proposed. γ-Butyrolactones have long been considered as synthetic objectives because they are widely found in biologically active natural products and molecules.1 In particular, chiral spirocyclic butyrolactones are core structural elements of many pharmaceutical value compounds.2 For example, spironolactone, a synthetic steroid, is a common agent for treating heart failure.3 Drospirenone is a potent component of marketed contraceptive called Yasmin.4 Biyouyanagin A, a natural product isolated from the leaves of H. chinense L. var. salicifolium, exhibits significant activity against HIV (Figure 1).5 In this context, the development of catalytic asymmetric

medicinal targets, it is still necessary to further enrich their diversity in this framework. Meanwhile, 1-indanone-containing compounds also have attracted much attention due to their bioactivities. 10 Accordingly, some unexpected medicinal value may be attained when the 1-indanone unit and butyrolactone motif are combined through a spiro-quaternary stereogenic carbon. To the best of our knowledge, the catalytic asymmetric synthesis of spiro(1-indanone-butyrolacones) is quite rare.11 In 2011, Marini et al. reported the Michael addition/cyclization reaction of 1-indanone derived tert-butyl β-ketoester and vinyl selenone to obtain spiro[1-indanone-3,2′-γ-butyrolactones] (Scheme 1a).11a Subsequently, Gade’s group described boxmi−Cu(II) complex catalyzed alkylation of 1-indanone-derived tert-butyl β-ketoester to generate spiro[1-indanone-3,2′-γ-butyrolactones] or bispiro[1-indanone-3,2′-γ-butyrolactones] (Scheme 1b).11b While high enantioselectivities were observed in both reports, the reactions still have the challenges of step-economy, substrate compatibility, and multiple stereocenters of products. Thus, the use of novel substrate combinations and the development of a new efficient asymmetric catalytic system may be the optimal way to address the issue. In the past few years, our group concentrated on the use of chiral dinuclear zinc cooperative catalyst, and it has been proven to be well-suited for various catalytic enantioselective

Figure 1. Pharmaceutical value compounds containing spirocyclic butyrolactone motifs.

methodologies for the construction of such motifs has become an attractive objective, and a amount of structurally diverse spirobutyrolactones have been obtained, such as spirooxindole butyrolactones,6 spiropyrrolidine butyrolactones,7 spirotetrahydrofuran butyrolactones,8 and spironaphthalenone butyrolactones.9 Owing to the prevalence of spirobutyrolactones in © XXXX American Chemical Society

Received: July 28, 2019

A

DOI: 10.1021/acs.orglett.9b02658 Org. Lett. XXXX, XXX, XXX−XXX

Letter

Organic Letters Table 1. Optimization of reaction conditionsa

Scheme 1. Strategies for the Formation of Chiral Spiro(1indanone-butyrolacones)

transformations,12,13 including Michael-initiated catalytic asymmetric tandem processes.13 Very recently, we successfully employed α-hydroxy 1-indanone 1 as donor in a cascade Michael/hemiketalization/Friedel−Crafts reaction,13a and a variety of 1-indanone containing bispirocyclic oxindoles were achieved with high stereoselectivities catalyzed by chiral dinuclear zinc complex. As part of our continuing study on dinuclear zinc catalyst, hence, we reported the one-step cascade Michael/transesterification reaction between αhydroxy-1-indanone and α,β-unsaturated esters through dinuclear zinc catalyst for the preparation of chiral spiro[1indanone-5,2′-γ-butyrolactones] containing two contiguous stereocenters (Scheme 1c). Initially, the model reaction of α-hydroxy-1-indanone 1a and α,β-unsaturated esters 2a was studied (Table 1). To our delight, in the presence of 5 mol % of ligand L1a and10 mol % of ZnEt2, the reaction proceeded smoothly in CH2Cl2 at 40 °C to provide the desired product 3aa in 76% yield with >20:1 dr value and 92% ee value (Table 1, entry 1). Encouraged by this promising result, we then examined a series of ligands with different substituents and structures, including AzePhenol ligands L1b and L1c and Trost’s ProPhenol ligands L2a−L2e. The results showed that the ligands displayed different catalytic efficiencies toward the same process (Table 1, entries 2−8), though they are similar in structure and function. As shown in Table 1, ligand 1a was found to be superior to other ligands considering both the yield and enantioselectivity. In order to improve the yield and stereoselectivity of this tandem reaction, further investigations were carried out, including the effects of solvent, catalyst loading amount, and reaction temperature (Table 1, entries 9−17). A survey of the solvent effects indicated that reaction medium played an important role in the reaction (Table 1, entries 9−13), and tetrahydrofuran (THF) proved to be the best choice with respect to efficiency and stereoselectivity (Table 1, entry 11). Increasing the catalyst loading amount to 10 mol % had no obvious improvement of the reaction results (Table 1, entry 14). When the catalyst loading amount was reduced to 2 mol %, the yield as well as enantioselectivity of 3aa were declined (Table 1, entry 15). We then evaluated the effect of temperature on this procedure (Table 1, entries 16 and 17). When the reaction temperature was lowered to 25 °C, the yield

entry

ligand

solvent

1 2 3 4 5 6 7 8 9 10 11 12 13 14e 15f 16 17

L1a L1b L1c L2a L2b L2c L2d L2e L1a L1a L1a L1a L1a L1a L1a L1a L1a

CH2Cl2 CH2Cl2 CH2Cl2 CH2Cl2 CH2Cl2 CH2Cl2 CH2Cl2 CH2Cl2 toluene 1,4-dioxane THF CHCl3 CH3CN THF THF THF THF

temp (°C) yieldb (%) 40 40 40 40 40 40 40 40 40 40 40 40 40 40 40 25 55

73 68 75 72 65 69 70 32 71 trace 79 72 23 80 44 50 90

drc

eed (%)

>20:1 >20:1 >20:1 >20:1 >20:1 >20:1 >20:1 >20:1 >20:1

92 88 91 85 86 79 81 71 89

>20:1 >20:1 >20:1 >20:1 >20:1 >20:1 >20:1

98 91 90 98 93 97 >99

a

Unless otherwise noted, all reactions were conducted with 1a (0.25 mmol), 2a (0.25 mmol), L (5 mol %), and ZnEt2 (10 mol %) in solvent (2 mL) under N2 for a suitable period of time. bIsolated yields. cDetermined by 1H NMR. dDetermined by HPLC analysis. e 10 mol % of ligand and 20 mol % of ZnEt2 were used. f2 mol % of ligand and 4 mol % of ZnEt2 were used.

was significantly declined (Table 1, entries 11 vs 16). When the temperature was increased to 55 °C, the yield of product 3aa was up to 90% with the ee value of up to >99% (Table 1, entry 17). With the optimized conditions in hand, the generality of this one-pot Michael addition/transesterification was explored. A series of α-hydroxy-1-indanones 1 were successfully reacted with 2a using 5 mol % of the dinuclear zinc−AzePhenol catalyst, and the results are shown in Table 2. Both electronwithdrawing and electron-donating groups (R1) at the 5position of benzene ring were well tolerated and had little impact on the yield, diastereoselectivities, or enantioselectivities (Table 2, entries 2−5). Moreover, 4-bromo-substituted 1f and 6-bromo-substituted 1g could also take part in this transformation to give the corresponding products 3fa and 3ga in 77−84% yields with >20:1 dr and >99% ee (Table 2, entries 6 and 7). Then we further expanded the scope of the reaction by engaging a variety of α,β-unsaturated esters 2 (Table 3). Both electron-rich and electron-deficient substituents on the R2 group performed well under the optimized conditions and delivered the chiral spirocyclic indanones 3ab−3al with high diastereoselectivities (up to >20:1) and enantioselectivities (up to 99% ee) (Table 3, entries 1−11), and the results showed that the electronic natures and positions of the substituents had very little influence on the stereoselectivities. The disubstituted substrates were also tested under the same B

DOI: 10.1021/acs.orglett.9b02658 Org. Lett. XXXX, XXX, XXX−XXX

Letter

Organic Letters Table 2. Substrate Scope of α-Hydroxy-1-indanonea

entry

R1

product

yieldb (%)

drc

eed (%)

1 2 3 4 5 6 7

H 5-F 5-Cl 5-Br 5-OMe 4-Br 6-Br

3aa 3ba 3ca 3da 3ea 3fa 3ga

90 85 82 89 87 77 84

>20:1 >20:1 >20:1 >20:1 >20:1 >20:1 >20:1

>99 >99 >99 99 99 >99 >99

obtained with 95−99% ee (Table 3, entries 19 and 20). Compared with the Michael/hemiketalization/Friedel−Crafts reaction using α-hydroxy 1-indanone 1 as donor,13a in most cases, α-hydroxy 1-indanone as donor in this reaction gave better results in yields (72−90%) and stereoselectivities (>20:1 dr, 95 → 99% ee). In addition, the relative and absolute configuration of product 3ad was determined unambiguously by X-ray crystallographic analysis. In order to investigate the practicality of this catalytic system, the reaction of α-hydroxy-1-indanone 1a and α,βunsaturated esters 2a was performed on a gram scale (Scheme 2). Under the optimal reaction conditions, the corresponding product 3aa was gained in 83% yield with >20:1 dr and 99% ee.

a

Unless otherwise noted, all reactions were conducted with 1 (0.25 mmol), 2a (0.25 mmol), L1a (5 mol %), and ZnEt2 (10 mol %) in THF (2 mL) under N2 at 55 °C for a suitable amount of time. b Isolated yields. cDetermined by1H NMR. dDetermined by HPLC analysis.

Scheme 2. Gram-Scale Reaction

Table 3. Substrate Scope of α,β-Unsaturated Estersa

entry

R2

product

yieldb (%)

drc

eed (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

4-FC6H4 4-ClC6H4 4-BrC6H4 4-MeC6H4 4-MeOC6H4 3-ClC6H4 3-BrC6H4 3-MeC6H4 3-MeOC6H4 2-BrC6H4 2-MeOC6H4 3-Br-4-ClC6H3 2-F-4-BrC6H3 2,4-Cl2C6H3 3,4-OCH2O−C6H3 1-naphthyl 2-naphthyl 2-thienyl H Me

3ab 3ac 3ad 3ae 3af 3ag 3ah 3ai 3aj 3ak 3al 3am 3an 3ao 3ap 3aq 3ar 3as 3at 3au

83 90 89 81 78 87 90 85 88 80 72 92 90 88 86 83 85 83 81 76

>20:1 >20:1 >20:1 >20:1 >20:1 >20:1 >20:1 >20:1 >20:1 >20:1 >20:1 >20:1 >20:1 >20:1 >20:1 >20:1 >20:1 >20:1

98 97 99 99 98 98 99 98 99 96 98 99 99 98 99 99 98 99 95 99

>20:1

On the basis of the configuration of the products and the previous reports,12b,c,14 we propose the following mechanism (Scheme 3). The dinuclear zinc complex ZnEtL1a is prepared Scheme 3. Proposed Catalytic Cycle

a

Unless otherwise noted, all reactions were conducted with 1a (0.25 mmol), 2 (0.25 mmol), L1a (5 mol %), and ZnEt2 (10 mol %) in THF (2 mL) under N2 at 55 °C for a suitable mount of time. b Isolated yields. cDetermined by 1H NMR. dDetermined by HPLC analysis.

spontaneously when ligand L1a is treated with 2 equiv of Et2Zn. Then the deprotonation of nucleophilic α-hydroxy-1indanone 1a afforded I. Subsequently, electrophilic α,βunsaturated esters 2a is activated by zinc−oxygen coordination to form II from the less hindered site. Next, the complex II undergoes Michael addition reaction to give intermediate III with the observed stereochemistry. Then desired product 3aa is delivered accompanied by the regeneration of zinc phenoxide species IV via the intramolecular transesterification of intermediate III. Finally, the catalytic cycle is restarted by the proton transfer of another α-hydroxy-1-indanone.

conditions, affording 3am−3ao in >20:1 dr with 98−99% ee (Table 3, entries 12−14). In addition, this protocol could be broadened to piperonyl-, 1-naphthyl-, and 2-naphthyl-substituted α,β-unsaturated esters and gave the products 3ap−3ar in >20:1 dr and 98−99% ee (Table 3, entries 15−17). Moreover, by varying the group R2 to 2-furanyl, the reaction also proceeded well, leading to product 3as in 83% yield with 99% ee value (Table 3, entry 18). Finally, nonaromatic substrates 2t and 2u were prepared and treated with 1a, respectively, and the corresponding products 3at and 3au were C

DOI: 10.1021/acs.orglett.9b02658 Org. Lett. XXXX, XXX, XXX−XXX

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Organic Letters

Chem. 2016, 59, 5121. (d) Tanaka, K.; Itazaki, H.; Yoshida, T. J. Antibiot. 1992, 45, 50. (e) Keyzers, R. A.; Daoust, J.; Davies-Coleman, M. T.; Soest, R. V.; Balgi, A.; Donohue, E.; Roberge, M.; Andersen, R. J. Org. Lett. 2008, 10, 2959. (3) (a) Pitt, B.; Zannad, F.; Remme, W. J.; Cody, R.; Castaigne, A.; Perez, A.; Palensky, J.; Wittes, J. N. N. Engl. J. Med. 1999, 341, 709. (b) Farquharson, C. A.; Struthers, A. D. Circulation 2000, 101, 594. (4) Elger, W.; Beier, S.; Pollow, K.; Garfield, R.; Shi, S. Q.; Hillisch, A. Steroids 2003, 68, 891. (5) (a) Tanaka, N.; Okasaka, M.; Ishimaru, Y.; Takaishi, Y.; Sato, M.; Okamoto, M.; Oshikawa, T.; Ahmed, S. U.; Consentino, L. M.; Lee, K.-H. Org. Lett. 2005, 7, 2997. (b) Nicolaou, K. C.; Wu, T. R.; Sarlah, D.; Shaw, D. M.; Rowcliffe, E.; Burton, D. R. J. Am. Chem. Soc. 2008, 130, 11114. (6) For reviews of the catalytic asymmetric synthesis of spirooxindole butyrolactones, see: (a) Murauski, K. J. R.; Jaworski, A. A.; Scheidt, K. A. Chem. Soc. Rev. 2018, 47, 1773. For selected examples, see: (b) Song, Z.-Y.; Chen, K.-Q.; Chen, X.-Y.; Ye, S. J. Org. Chem. 2018, 83, 2966. (c) Gao, Y.; Ma, Y.; Xu, C.; Li, L.; Yang, T.; Sima, G.; Fu, Z.; Huang, W. Adv. Synth. Catal. 2018, 360, 479. (d) Chen, X.-Y.; Chen, K.-Q.; Sun, D.-Q.; Ye, S. Chem. Sci. 2017, 8, 1936. (e) Xu, J.; Yuan, S.; Miao, M.; Chen, Z. J. Org. Chem. 2016, 81, 11454. (f) Xie, Y.; Yu, C.; Li, T.; Tu, S.; Yao, C. Chem. - Eur. J. 2015, 21, 5355. (g) Dugal-Tessier, J.; O’Bryan, E. A.; Schroeder, T. B. H.; Cohen, D. T.; Scheidt, K. A. Angew. Chem., Int. Ed. 2012, 51, 4963. (h) Li, J.-L.; Sahoo, B.; Daniliuc, C.-G.; Glorius, F. Angew. Chem., Int. Ed. 2014, 53, 10515. (i) Jin, Z.; Jiang, K.; Fu, Z.; Torres, J.; Zheng, P.; Yang, S.; Song, B.-A.; Chi, Y. R. Chem. - Eur. J. 2015, 21, 9360. (j) Chen, L.; Wu, Z.-J.; Zhang, M.-L.; Yue, D.-F.; Zhang, X.-M.; Xu, X.-Y.; Yuan, W.-C. J. Org. Chem. 2015, 80, 12668. (k) Wang, Q.-L.; Peng, L.; Wang, F.-Y.; Zhang, M.-L.; Jia, L.-N.; Tian, F.; Xu, X.-Y.; Wang, L.-X. Chem. Commun. 2013, 49, 9422. (l) Guo, Y.; Meng, C.; Liu, X.; Li, C.; Xia, A.; Xu, Z.; Xu, D. Org. Lett. 2018, 20, 913. (m) Trost, B. M.; Hirano, K. Org. Lett. 2012, 14, 2446. (n) Murata, Y.; Takahashi, M.; Yagishita, F.; Sakamoto, M.; Sengoku, T.; Yoda, H. Org. Lett. 2013, 15, 6182. (o) Bergonzini, G.; Melchiorre, P. Angew. Chem., Int. Ed. 2012, 51, 971. (p) Ming, S.; Zhao, B.-L.; Du, D.-M. Org. Biomol. Chem. 2017, 15, 6205. (7) For examples of catalytic asymmetric synthesis of spiropyrrolidine butyrolactones, see: (a) Liu, T.-L.; He, Z.-L.; Tao, H.-Y.; Wang, C.-J. Chem. - Eur. J. 2012, 18, 8042. (b) Cayuelas, A.; Ortiz, R.; Najera, C.; Sansano, J. M.; Larranaga, O.; de Cozar, A.; Cossío, F. P. Org. Lett. 2016, 18, 2926. (c) Chen, N.; Zhu, L.; Gan, L.; Liu, Z.; Wang, R.; Cai, X.; Jiang, X. Eur. J. Org. Chem. 2018, 2018, 2939. (8) For examples of catalytic asymmetric synthesis of spirotetrahydrofuran butyrolactones, see: Cala, L.; Mendoza, A.; Fananas, F. J.; Rodrıguez, F. Chem. Commun. 2013, 49, 2715. (9) For examples of catalytic asymmetric synthesis of spironaphthalenone butyrolactones, see: (a) Dohi, T.; Takenaga, N.; Nakae, T.; Toyoda, Y.; Yamasaki, M.; Shiro, M.; Fujioka, H.; Maruyama, A.; Kita, Y. J. Am. Chem. Soc. 2013, 135, 4558. (b) Dohi, T.; Maruyama, A.; Takenaga, N.; Senami, K.; Minamitsuji, Y.; Fujioka, H.; Caemmerer, S. B.; Kita, Y. Angew. Chem., Int. Ed. 2008, 47, 3787. (c) Uyanik, M.; Yasui, T.; Ishihara, K. Angew. Chem., Int. Ed. 2010, 49, 2175. (d) Hempel, C.; Maichle-Mössmer, C.; Pericàs, M. A.; Nachtsheim, B. J. Adv. Synth. Catal. 2017, 359, 2931. (e) Uyanik, M.; Yasui, T.; Ishihara, K. Tetrahedron 2010, 66, 5841. (10) For reviews, see: (a) Patil, S. A.; Patil, R.; Patil, S. A. Eur. J. Med. Chem. 2017, 138, 182. For select examples, see: (b) Nagle, D. G.; Zhou, Y.-D.; Park, P. U.; Paul, V. J.; Rajbhandari, I.; Duncan, C. J. G.; Pasco, D. S. J. Nat. Prod. 2000, 63, 1431. (c) Kim, S.-H.; Kwon, S. H.; Park, S.-H.; Lee, J. K.; Bang, H.-S.; Nam, S.-J.; Kwon, H. C.; Shin, J.; Oh, D.-C. Org. Lett. 2013, 15, 1834. (d) Girgis, A. S. Eur. J. Med. Chem. 2009, 44, 91. (e) Wei, A. C.; Ali, M. A.; Yoon, Y. K.; Ismail, R.; Choon, T. S.; Kumar, R. S. Bioorg. Med. Chem. Lett. 2013, 23, 1383. (11) (a) Sternativo, S.; Calandriello, A.; Costantino, F.; Testaferri, L.; Tiecco, M.; Marini, F. Angew. Chem., Int. Ed. 2011, 50, 9382. (b) Deng, Q.-H.; Wadepohl, H.; Gade, L. H. J. Am. Chem. Soc. 2012, 134, 2946. For an example of diastereoselective synthesis of spiro(1-

In conclusion, we have developed an efficient chiral dinuclear zinc−AzePhenol complex catalytic one step cascade Michael addition/transesterification reaction between αhydroxy-1-indanones and α,β-unsaturated esters. This strategy allows the constitution of a large range of structurally novel spiro[1-indanone-5,2′-γ-butyrolactones] in excellent diastereoand enantioselectivities under mild conditions. This is the first catalytic asymmetric approach to spiro(1-indanone-butyrolacones) containing two adjacent stereocenters staring from αhydroxy 1-indanone. In addition, this protocol can be run on a gram scale without a loss of stereoselectivity. Finally, a possible mechanism is proposed.

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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.9b02658. Screening tables, experimental procedures, compound characterization data, NMR spectra, and HPLC traces (PDF) Accession Codes

CCDC 1887101 contains 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.

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AUTHOR INFORMATION

Corresponding Authors

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

Jun-Biao Chang: 0000-0001-6236-1256 Min-Can Wang: 0000-0002-3817-3607 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We are grateful to the National Natural Science Foundation of China (NNSFC 21871237, NNSFC 81330075). REFERENCES

(1) For selected reviews, see: (a) Bartoli, A.; Rodier, F.; Commeiras, L.; Parrain, J.-L.; Chouraqui, G. Nat. Prod. Rep. 2011, 28, 763. (b) Mao, B.; Fananas-Mastral, M.; Feringa, B. L. Chem. Rev. 2017, 117, 10502. (c) Hoffmann, H. M. R.; Rabe, J. Angew. Chem., Int. Ed. Engl. 1985, 24, 94. (d) Seitz, M.; Reiser, O. Curr. Opin. Chem. Biol. 2005, 9, 285. (e) Kitson, R. R. A.; Millemaggi, A.; Taylor, R. J. K. Angew. Chem., Int. Ed. 2009, 48, 9426. (f) Takano, E. Curr. Opin. Microbiol. 2006, 9, 287. (g) Teplitski, M.; Mathesius, U.; Rumbaugh, K. P. Chem. Rev. 2011, 111, 100. (h) Lee, S. H.; Park, O. J. Appl. Microbiol. Biotechnol. 2009, 84, 817. (i) Lepoittevin, J. P.; Berl, V.; Arnau, E. G. Chem. Rec. 2009, 9, 258. (2) For reviews, see: (a) Quintavalla, A. Curr. Med. Chem. 2018, 25, 917. (b) Kolkhof, P.; Bärfacker, L. J. Endocrinol. 2017, 234, 125. For selected examples, see: (c) Rana, S.; Blowers, E. C.; Tebbe, C.; Contreras, J. I.; Radhakrishnan, P.; Kizhake, S.; Zhou, T.; Rajule, R. N.; Arnst, J. L.; Munkarah, A. R.; Rattan, R.; Natarajan, A. J. Med. D

DOI: 10.1021/acs.orglett.9b02658 Org. Lett. XXXX, XXX, XXX−XXX

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Organic Letters indanone-butyrolacones), see: (c) Ko, T. Y.; Youn, S. W. Adv. Synth. Catal. 2016, 358, 1934. (12) (a) Hua, Y.-Z.; Lu, L.-J.; Huang, P.-J.; Wei, D.-H.; Tang, M.-S.; Wang, M.-C.; Chang, J.-B. Chem. - Eur. J. 2014, 20, 12394. (b) Hua, Y.-Z.; Yang, X.-C.; Liu, M.-M.; Song, X.-X.; Wang, M.-C.; Chang, J.-B. Macromolecules 2015, 48, 1651. (c) Hua, Y.-Z.; Han, X.-W.; Yang, X.C.; Song, X.; Wang, M.-C.; Chang, J.-B. J. Org. Chem. 2014, 79, 11690. (d) Liu, S.; Gao, W.-C.; Miao, Y.-H.; Wang, M.-C. J. Org. Chem. 2019, 84, 2652. (e) Gao, Y.-Y.; Hua, Y.-Z.; Wang, M.-C. Adv. Synth. Catal. 2018, 360, 80. (f) Liu, S.; Shao, N.; Li, F.-Z.; Yang, X.C.; Wang, M.-C. Org. Biomol. Chem. 2017, 15, 9465. (13) (a) Liu, M.-M.; Yang, X.-C.; Hua, Y.-Z.; Chang, J.-B.; Wang, M.-C. Org. Lett. 2019, 21, 2111. (b) Yang, X.-C.; Liu, M.-M.; Mathey, F.; Yang, H.; Hua, Y.-Z.; Wang, M.-C. J. Org. Chem. 2019, 84, 7762. (c) Tao, B.-K.; Yang, H.; Hua, Y.-Z.; Wang, M.-C. Org. Biomol. Chem. 2019, 17, 4301. (d) Hua, Y.-Z.; Liu, M.-M.; Huang, P.-J.; Song, X.; Wang, M.-C.; Chang, J.-B. Chem. - Eur. J. 2015, 21, 11994. (14) (a) Xiao, Y.-L.; Wang, Z.; Ding, K.-L. Chem. - Eur. J. 2005, 11, 3668. (b) Xiao, Y.-L.; Wang, Z.; Ding, K.-L. Macromolecules 2006, 39, 128.

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DOI: 10.1021/acs.orglett.9b02658 Org. Lett. XXXX, XXX, XXX−XXX