Letter Cite This: Org. Lett. XXXX, XXX, XXX−XXX
pubs.acs.org/OrgLett
Trapping of Zwitterionic Intermediates by Isatins and Imines: Synthesis of Benzoxazines Bearing a C4-Quaternary Stereocenter Shikun Jia,† Xi Yang,‡ Guizhi Dong,† Chaoqun Ao,† Xianxing Jiang,† and Wenhao Hu*,† †
Guangdong Key Laboratory of Chiral Molecule and Drug Discovery, School of Pharmaceutical Sciences, Sun Yat-sen University, Guangzhou 510006, China ‡ Shanghai Engineering Research Center of Molecular Therapeutics and New Drug Development, School of Chemistry and Molecular Engineering, East China Normal University, Shanghai 200062, China
Org. Lett. Downloaded from pubs.acs.org by UNIV OF ROCHESTER on 05/13/19. For personal use only.
S Supporting Information *
ABSTRACT: Benzoxazines bearing a C4-quaternary stereocenter have been accomplished via the rhodium-catalyzed electrophilic trapping of zwitterionic intermediates by isatins and imines, respectively. The key intermediates of the strategy are proposed to generate from the reaction of donor−acceptor rhodium carbenes with secondary amides. Usage of chiral BINOL-phosphoric acid co-catalyst resulted in enrichment of enantioselectivity in the trapping process with imines.
B
Over the past few decades, transition-metal-catalyzed metal carbene reactions have been employed as useful tools for the construction of diverse organic molecules.9 Utilizing the metalcarbene reactivity, pioneering developments have been made in multicomponent reactions (MCRs) by various research groups and also by us. Transition-metal-catalyzed trapping of metal-carbene-induced active intermediates such as oxonium ylides10 (generated from alcohols) or ammonium ylides11 (generated from amines), as well as zwitterionic intermediates12 (generated from indole, pyrrole, N-substituted aniline) using different electrophiles to deliver elegant molecular entities, has become a power strategy in this context (Scheme 1a). Recently, Reddy et al.,13 reported an efficient [1,4]-proton transfer process of zwitterionic intermediate, obtained from reaction of donor−acceptor metal-carbene and secondary amide, to yield the corresponding 2-aryl-4H-benzo[d][1,3]oxazine (Scheme 1b, path A). In continuation to our ongoing interests toward the construction of polyfunctional heterocycles based on electrophilic trapping process, we conceived that the trapping of these zwitterionic intermediates by suitable electrophiles may provide easy access to benzoxazines bearing C4-quaternary stereocenter (Scheme 1b, path B). Furthermore, it was anticipated that the asymmetric control could be realized during the trapping process by utilizing an appropriate chiral catalyst such as chiral phosphoric acid. Herein, we report a novel approach for the synthesis of benzoxazines bearing a C4-quaternary stereocenter via the rhodium-catalyzed electrophilic trapping of zwitterionic intermediates using isatins and imines, respectively. Initially, the synthetic strategy was tested with the reaction of methyl 2-(2-benzamidophenyl)-2-diazoacetate 1a and 1-
enzoxazines containing a quaternary stereocenter at the C4 carbon have drawn immense research attention, because of their abundance in many pharmaceutically active molecules and biologically relevant products1 such as anticonvulsant (A),2 fungicide (B),3 and potent nonsteroidal progesterone receptor agonists (C)4 (see Figure 1).
Figure 1. Representative bioactive benzoxazine derivatives bearing a C4-quaternary stereocenter.
Therefore, the development of practical methods to achieve this building block, bearing a quaternary stereocenter at the C4 position, is an attractive subject in organic synthesis. Recently, a variety of efficient strategies have been developed successfully toward the construction of benzoxazine ring, which includes the cyclization of olefinic amide using different electrophiles,5 direct C−H bond oxygenation 6 and oxycyanation of methylenecyclopropanes.7 On the other hand, the research group of Toste has established an enantioselective halocyclization for the synthesis of chiral benzoxazine derivatives by applying the concept of chiral anion phase-transfer catalysis.8 However, most of these methods are relatively less atomeconomic and rarely access the chiral quaternary stereocenter at the C4 carbon. Despite these achievements, the development of a highly atom-economic and novel enantioselective protocol for the construction of such skeletons is highly desirable. © XXXX American Chemical Society
Received: April 5, 2019
A
DOI: 10.1021/acs.orglett.9b01207 Org. Lett. XXXX, XXX, XXX−XXX
Letter
Organic Letters
product 3a in similar yields, albeit with moderate diastereoselectivity. With the optimized reaction conditions in hand, we first examined the substrate scope of isatins 2 by reacting them with methyl 2-(2-benzamidophenyl)-2-diazoacetate 1a. As shown in Scheme 2, substituents (from electron donating to electron
Scheme 1. Typical Multicomponent Trapping and Our Strategy for the Synthesis of Benzoxazines Bearing a 4°(C4)-Stereocenter
Scheme 2. Scope of the Diazoacetates and Isatinsa,b,c
methylindoline-2,3-dione 2a in the presence of [Rh2(OAc)4] catalyst and 4 Å molecular sieves at room temperature in dichloromethane. To our delight, the desired product 3a was obtained in 80% yield, but with poor diastereoselective ratio (52:48; see Table 1, entry 1). Various solvents were then Table 1. Condition Optimizationa
entry
T (°C)
solvent
yieldb (%)
diastereomeric ratio, dr (syn:anti)c
1 2 3 4 5 6 7
rt rt rt rt rt 0 40
DCM THF 2-MeTHF EA Et2O THF THF
80 96 78 71 69 82 89
52:48 89:11 86:14 75:25 70:30 83:17 74:26
a Reaction conditions: 2a (0.1 mmol), Rh2(OAc)4 (0.001 mmol), 4 Å molecular sieves (100 mg), solvent (1.5 mL); 1a (0.15 mmol) in solvent (1 mL) was added under an inert atmosphere over 60 min. b Isolated yields after purification by column chromatography. c Determined by 1H NMR of the crude reaction mixture.
screened to enhance the yield and diastereoselectivity of 3a. The reaction was found to be effective in THF and afforded the desired product in 96% yield and with very good diastereoselectivity, 89:11 (Table 1, entries 2−5). Reduction in both the yield and diastereoselectivity of the desired product 3a was observed with the reaction at 0 °C in the optimal solvent, THF (Table 1, entry 6). Further investigation of the reaction at elevated temperature (40 °C), gave the desired
a Reaction conditions: 2 (0.3 mmol), Rh2(OAc)4 (0.003 mmol), 4 Å molecular sieves (100 mg), THF (1.5 mL); 1 (0.45 mmol) in THF (2 mL) was added under an inert atmosphere over 60 min at 25 °C. b Isolated yields after purification by column chromatography. cThe diastereomeric ratio (dr) (syn:anti) parameter was determined by 1H NMR of the crude reaction mixture. dRunning with corresponding diazo compound precursor (1.0 mmol) and 1a (0.5 mmol).
B
DOI: 10.1021/acs.orglett.9b01207 Org. Lett. XXXX, XXX, XXX−XXX
Letter
Organic Letters Scheme 3. Scope of Iminesa,b,c
withdrawing) at the C-5 position of isatins 2 gave the desired products 3a−3f in high yields with good diastereoselectivities. Meanwhile, we found that substituents on other positions of isatins 2 did not affect the efficiency of reaction (3g−3j). For example, the reaction with 4-chloro-1-methylindoline-2,3dione proceeded well to give the expected product 3j in 92% yield and 80:20 diastereoselectivity. The steric hindrance might account for the decrease of diastereoselectivity. Next, various diazoacetates 1 have been examined against 1methylindoline-2,3-dione 2a under optimal conditions. The current strategy showed very good substrate scope bearing different aryl-substituted diazoacetates 1 and resulting in the desired products in excellent yields with very good diastereoselectivities (3k−3t). In addition, heterocyclic (thienyl) tethered substrate gave the corresponding product 3q in 81% yield, along with 81:19 diastereoselectivity. Similarly, naphthyl substrate was also amenable and resulted in the product 3p in good yields. Notably, diazo compounds associated with a diaryl urea component were also compatible and furnished the expected products 3u−3x in 84%−92% yields, yet, with low diastereoselectivities. In addition, a gramscale reaction was performed using 3 mmol of 1a and 2 mmol 2a under standard conditions to give the desired product 3a in 91% yield (0.78 g) with 86:14 diastereoselectivity. The structure and relative configuration of the desired product 3 was unambiguously determined by X-ray analysis of 3a, which was confirmed to be syn-product. In order to explore the asymmetric 4° stereocenter generation at the C4-carbon, subsequently, we turned our attention to realize the enantioselective trapping of zwitterionic intermediate by imines in the presence of Rh/chiral phosphoric acid co-catalysts to produce chiral benzoxazine derivatives. After an extensive screening of reaction conditions with various combinations of reaction parameters such as catalyst, chiral phosphoric acid, solvent, and the reaction temperature, we found that 1 mol % of Rh2(esp)2 catalyst, 10 mol % of (R)-3,3′-bis(9-phenanthryl)-binol phosphoric acid (PA-1e) co-catalyst, CHCl3 solvent and −20 °C temperature were optimal for the success of the reaction to yield the desired product in very good yield with excellent enatioselectivity.14 The scope of imines was next examined under the optimal reaction conditions. As shown in Scheme 3, many substituted aryl imines could participate in the reaction to give the corresponding product in good yields and enhanced diastereoselectivities. It is noteworthy that the asymmetric control proceeded successfully in the case of syn-isomer of the desired product, even with large scale, and lower ee values were observed for the anti-isomer. Meanwhile, imines derived from electron-deficient anilines afforded the desired products with slightly lower enantioselectivities (Scheme 3, 5j and 5k). Then, finally, the absolute configuration of the desired product 5 was unambiguously determined by X-ray analysis of syn-5f. To acquire the mechanistic insight of the reaction pathway, control experiments were conducted to verify whether the generation of C4-quaternary center proceeds via a stepwise reaction pathway or a concerted reaction pathway. Thus, the O−H insertion products 6 and 7 were isolated and then reacted with isatin and imine under optimized reaction conditions, respectively. None of these reactions ultimately delivered the desired products 3m and 5a, which excluded the possibility of a stepwise O−H insertion/addition pathway and therefore concluded the direct trapping of zwitterioinc intermediate. (See Scheme 4.)
a Reaction conditions: 4 (0.2 mmol), Rh2(OAc)4 (0.002 mmol), PA1e (0.02 mmol), 4 Å molecular sieves (100 mg), CHCl3 (1 mL); 1l (0.26 mmol) in CHCl3 (1 mL) was added under an inert atmosphere over 60 min. bIsolated yields after purification by column chromatography. cThe diastereomeric ratio (dr) (syn:anti) parameter was determined by 1H NMR of the crude reaction mixture. dThe enantiomeric excess (ee) value (syn isomer/anti isomer) was determined by HPLC analysis, using a chiral stationary phase.
Scheme 4. Control Experiments
C
DOI: 10.1021/acs.orglett.9b01207 Org. Lett. XXXX, XXX, XXX−XXX
Organic Letters
■
Based on the experimental results and previous literature reports,10a,13 a plausible reaction mechanism for the electrophilic trapping reactions is illustrated in Scheme 5. First, 2-(2-
Letter
AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. ORCID
Scheme 5. Proposed Reaction Mechanism
Xianxing Jiang: 0000-0002-7508-2368 Wenhao Hu: 0000-0002-1461-3671 Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS We acknowledge the financial support from Guangdong Innovative and Entrepreneurial Research Team Program (No. 2016ZT06Y337). Project funded by China Postdoctoral Science Foundation (No. 2018M633258) is also greatly acknowledged. We thank Dr. A. Gopi Krishna Reddy (Sun Yat-sen University) for assistance with manuscript revision.
■
arylamidophenyl)-2-diazoacetate 1 forms metal carbene A in the presence of Rh2(OAc)4. The reaction of metal carbene A with the carbonyl of amide 1 leads to zwitterionic intermediate B-1 or its enolate form B-2. Subsequent trapping of B-1/B-2 with isatin to generate intermediate C, which undergoes a delayed H transfer to give the desired product. On the other hand, hydrogen-bonding interactions between zwitterionic intermediate B and imine 4 may facilitate the trapping process, thus, promoting efficient chirality induction to intermediate C, which later converts to chiral benzoxazine 5 via similar delayed H transfer (please see the Supporting Information for the description of preferential diastereoselectivities and enantioselectivities). In summary, we have developed an efficient method for the construction of benzoxazine derivatives bearing a C4quaternary stereocenter. The desired products are obtained in excellent yields with good diastereoselectivities via a rhodium-catalyzed electrophilic trapping of zwitterionic intermediates using isatins. Furthermore, chiral benzoxazine derivatives have been achieved in good yields with high enantioselectivities with imines in the presence of Rh/chiral phosphoric acid co-catalysts. These transformations not only offer a novel way for the construction of benzoxazine skeleton, but also enrich our electrophilic trapping strategy in the synthesis of complex compounds.
■
REFERENCES
(1) (a) Dias, N.; Goossens, J.-F.; Baldeyrou, B.; Lansiaux, A.; Colson, P.; Di Salvo, A.; Bernal, J.; Turnbull, A.; Mincher, D. J.; Bailly, C. Oxoazabenzo[de]anthracenes Conjugated to Amino Acids: Synthesis and Evaluation as DNA-Binding Antitumor Agents. Bioconjugate Chem. 2005, 16, 949−958. (b) Hays, S. J.; Caprathe, B. W.; Gilmore, J. L.; Amin, N.; Emmerling, M. R.; Michael, W.; Nadimpalli, R.; Nath, R.; Raser, K. J.; Stafford, D.; Watson, D.; Wang, K.; Jaen, J. C. 2-Amino-4H-3,1-benzoxazin-4-ones as Inhibitors of C1r Serine Protease. J. Med. Chem. 1998, 41, 1060−1067. (c) Krantz, A.; Spencer, R. W.; Tam, T. F.; Liak, T. J.; Copp, L. J.; Thomas, E. M.; Rafferty, S. P. Design and synthesis of 4H-3,1-benzoxazin-4-ones as potent alternate substrate inhibitors of human leukocyte elastase. J. Med. Chem. 1990, 33, 464−479. (d) Kobzina, J. W. Herbicidal Nhaloacetyl-1,2-dihydro-4H-3,1-benzoxazine. U.S. Patent No. US4030906, 1977. (e) Tsubuki, T.; Sagawa, T.; Funada, K.; Araya, I. Maleic Acid Salt and Crystal Thereof. International Patent No. WO2011036895, 2011. (2) Kuch, H.; Schmitt, K.; Seidl, G.; Hoffmann, I. 1,2-amino-4,4-disubstituted-4H-3,1-benzoxazines. U.S. Patent No. US3725404, 1973. (3) Sugiyama, H.; Hosoda, K.; Kumagai, Y.; Takeuchi, M.; Okada, M. 4H-3,1-benzoxazine derivatives, process for producing the same and agricultural or horticultural fungicide containing the same. U.S. Patent No. US4596801, 1986. (4) Zhang, P.; Terefenko, E. A.; Fensome, A.; Zhang, Z.; Zhu, Y.; Cohen, J.; Winneker, R.; Wrobel, J.; Yardley, J. Potent nonsteroidal progesterone receptor agonists: Synthesis and SAR study of 6-aryl benzoxazines. Bioorg. Med. Chem. Lett. 2002, 12, 787−790. (5) (a) Zhao, J.-F.; Duan, X.-H.; Yang, H.; Guo, L.-N. TransitionMetal-Free Oxyfluorination of Olefinic Amides for the Synthesis of Fluorinated Heterocycles. J. Org. Chem. 2015, 80, 11149−11155. (b) Deng, Q.-H.; Chen, J.-R.; Wei, Q.; Zhao, Q.-Q.; Lu, L.-Q.; Xiao, W.-J. Visible-light-induced photocatalytic oxytrifluoromethylation of N-allylamides for the synthesis of CF3-containing oxazolines and benzoxazines. Chem. Commun. 2015, 51, 3537−3540. (c) Jana, S.; Ashokan, A.; Kumar, S.; Verma, A.; Kumar, S. Copper-catalyzed trifluoromethylation of alkenes: synthesis of trifluoromethylated benzoxazines. Org. Biomol. Chem. 2015, 13, 8411−8415. (d) Fu, W.; Han, X.; Zhu, M.; Xu, C.; Wang, Z.; Ji, B.; Hao, X.-Q.; Song, M.P. Visible-light-mediated radical oxydifluoromethylation of olefinic amides for the synthesis of CF2H-containing heterocycles. Chem. Commun. 2016, 52, 13413−13416. (e) Chu, X.-Q.; Xu, X.-P.; Meng, H.; Ji, S.-J. Synthesis of functionalized benzoxazines by coppercatalyzed C(sp3)−H bond functionalization of acetonitrile with olefinic amides. RSC Adv. 2015, 5, 67829−67832. (f) Yang, H.; Duan, X.-H.; Zhao, J.-F.; Guo, L.-N. Transition-Metal-Free Tandem Radical Thiocyanooxygenation of Olefinic Amides: A New Route to SCN-Containing Heterocycles. Org. Lett. 2015, 17, 1998−2001.
ASSOCIATED CONTENT
* Supporting Information S
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.orglett.9b01207. Experimental procedure and spectroscopic data for all compounds (PDF) Accession Codes
CCDC 1532376 and 1533726 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. D
DOI: 10.1021/acs.orglett.9b01207 Org. Lett. XXXX, XXX, XXX−XXX
Letter
Organic Letters
ketones. Chem. Commun. 2014, 50, 951−953. (c) Ma, X.; Jiang, J.; Lv, S.; Yao, W.; Yang, Y.; Liu, S.; Xia, F.; Hu, W. An Ylide Transformation of Rhodium(I) Carbene: Enantioselective Three-Component Reaction through Trapping of Rhodium(I)-Associated Ammonium Ylides by β-Nitroacrylates. Angew. Chem., Int. Ed. 2014, 53, 13136−13139. (d) Zhu, C.; Xu, G.; Sun, J. Gold-Catalyzed Formal [4 + 1]/[4 + 3] Cycloadditions of Diazo Esters with Triazines. Angew. Chem., Int. Ed. 2016, 55, 11867−11871. (e) Nicolle, S. M.; Lewis, W.; Hayes, C. J.; Moody, C. J. Stereoselective Synthesis of Functionalized Pyrrolidines by the Diverted N−H Insertion Reaction of Metallocarbenes with βAminoketone Derivatives. Angew. Chem., Int. Ed. 2016, 55, 3749− 3753. (f) Zhou, C.-Y.; Wang, J.-C.; Wei, J.; Xu, Z.-J.; Guo, Z.; Low, K.-H.; Che, C.-M. Dirhodium Carboxylates Catalyzed Enantioselective Coupling Reactions of α-Diazophosphonates, Anilines, and Electron-Deficient Aldehydes. Angew. Chem., Int. Ed. 2012, 51, 11376−11380. (12) (a) Qiu, H.; Li, M.; Jiang, L.-Q.; Lv, F.-P.; Zan, L.; Zhai, C.-W.; Doyle, M. P.; Hu, W.-H. Highly enantioselective trapping of zwitterionic intermediates by imines. Nat. Chem. 2012, 4, 733−738. (b) Zhang, D.; Qiu, H.; Jiang, L.; Lv, F.; Ma, C.; Hu, W. Enantioselective Palladium(II) Phosphate Catalyzed Three-Component Reactions of Pyrrole, Diazoesters, and Imines. Angew. Chem., Int. Ed. 2013, 52, 13356−13360. (c) Zhang, D.; Zhou, J.; Xia, F.; Kang, Z.; Hu, W. Bond cleavage, fragment modification and reassembly in enantioselective three-component reactions. Nat. Commun. 2015, 6, 5801−5808. (d) Jia, S.; Xing, D.; Zhang, D.; Hu, W. Catalytic Asymmetric Functionalization of Aromatic C-H Bonds by Electrophilic Trapping of Metal-Carbene-Induced Zwitterionic Intermediates. Angew. Chem., Int. Ed. 2014, 53, 13098−13101. (e) Jia, S.; Lei, Y.; Song, L.; Krishna Reddy, A. G.; Xing, D.; Hu, W. Diastereoselective Intramolecular Aldol-Type Trapping of Zwitterionic Intermediates by Ketones for the Synthesis of Spiro[chroman4,3′-oxindole] Derivatives. Adv. Synth. Catal. 2017, 359, 58−63. (f) Zhang, D.; Hu, W. Asymmetric Multicomponent Reactions Based on Trapping of Active Intermediates. Chem. Rec. 2017, 17, 739−753. (13) Subba Reddy, B. V.; Babu, R. A.; Ramana Reddy, M.; Mohan Reddy, B. J.; Sridhar, B. Intramolecular C−O/C−S bond insertion of α-diazoesters for the synthesis of 2-aryl-4H-benzo[d][1,3]oxazine and 2-aryl-4H-benzo[d][1,3]thiazine derivatives. RSC Adv. 2014, 4, 44629−44633. (14) For details, see the Supporting Information.
(g) Wang, J.; Sang, R.; Chong, X.; Zhao, Y.; Fan, W.; Li, Z.; Zhao, J. Copper-catalyzed radical cascade oxyalkylation of olefinic amides with simple alkanes: highly efficient access to benzoxazines. Chem. Commun. 2017, 53, 7961−7964. (6) (a) Wang, Y.-F.; Chen, H.; Zhu, X.; Chiba, S. Copper-Catalyzed Aerobic Aliphatic C−H Oxygenation Directed by an Amidine Moiety. J. Am. Chem. Soc. 2012, 134, 11980−11983. (b) Li, Y.; Li, Z.; Xiong, T.; Zhang, Q.; Zhang, X. Copper-Catalyzed Selective Benzylic C−O Cyclization of N-o-Tolylbenzamides: Synthesis of 4H-3,1-Benzoxazines. Org. Lett. 2012, 14, 3522−3525. (7) Yuan, Y.-C.; Yang, H.-B.; Tang, X.-Y.; Wei, Y.; Shi, M. Unprecedented Oxycyanation of Methylenecyclopropanes for the Facile Synthesis of Benzoxazine Compounds Containing a Cyano Group. Chem. - Eur. J. 2016, 22, 5146−5150. (8) Wang, Y.-M.; Wu, J.; Hoong, C.; Rauniyar, V.; Toste, F. D. Enantioselective Halocyclization Using Reagents Tailored for Chiral Anion Phase-Transfer Catalysis. J. Am. Chem. Soc. 2012, 134, 12928− 12931. (9) (a) Davies, H. M. L.; Alford, J. S. Reactions of metallocarbenes derived from N-sulfonyl-1,2,3-triazoles. Chem. Soc. Rev. 2014, 43, 5151−5162. (b) Cheng, Q.-Q.; Deng, Y.-M.; Lankelma, M.; Doyle, M. P. Cycloaddition reactions of enoldiazo compounds. Chem. Soc. Rev. 2017, 46, 5425−5443. (c) Xia, Y.; Qiu, D.; Wang, J. TransitionMetal-Catalyzed Cross-Couplings through Carbene Migratory Insertion. Chem. Rev. 2017, 117, 13810−13889. (d) Liu, L.; Zhang, J. Gold-catalyzed transformations of α-diazocarbonyl compounds: selectivity and diversity. Chem. Soc. Rev. 2016, 45, 506−516. (e) Pei, C.; Zhang, C.; Qian, Y.; Xu, X.-F. Catalytic carbene/alkyne metathesis (CAM): a versatile strategy for alkyne bifunctionalization. Org. Biomol. Chem. 2018, 16, 8677−8685. (f) Ren, Y.; Zhu, S.; Zhou, Q. Chiral proton-transfer shuttle catalysts for carbene insertion reactions. Org. Biomol. Chem. 2018, 16, 3087−3094. (10) (a) Guo, X.; Hu, W. Novel Multicomponent Reactions via Trapping of Protic Onium Ylides with Electrophiles. Acc. Chem. Res. 2013, 46, 2427−2440. (b) Shi, T.; Guo, X.; Teng, S.; Hu, W. Pd(II)catalyzed formal [4 + 1] cycloaddition reactions of diazoacetates and aryl propargyl alcohols to form 2,5-dihydrofurans. Chem. Commun. 2015, 51, 15204−15207. (c) Alavala, G. K. R.; Sajjad, F.; Shi, T.; Kang, Z.; Ma, M.; Xing, D.; Hu, W. Diastereoselective synthesis of isochromans via the Cu(II)-catalysed intramolecular Michael-type trapping of oxonium ylides. Chem. Commun. 2018, 54, 12650−12653. (d) Wei, H.; Bao, M.; Dong, K.; Qiu, L.; Wu, B.; Xu, X.; Hu, W. Enantioselective Oxidative Cyclization/Mannich Addition Enabled by Gold(I)/Chiral Phosphoric Acid Cooperative Catalysis. Angew. Chem., Int. Ed. 2018, 57, 17200−17204. (e) Kang, Z.; Wang, Y.; Zhang, D.; Wu, R.; Xu, X.; Hu, W. Asymmetric Counter-AnionDirected Aminomethylation: Synthesis of Chiral β-Amino Acids via Trapping of an Enol Intermediate. J. Am. Chem. Soc. 2019, 141, 1473−1478. (f) Nicolle, S. M.; Lewis, W.; Hayes, C. J.; Moody, C. J. Stereoselective Synthesis of Highly Substituted Tetrahydrofurans through Diverted Carbene O-H Insertion Reaction. Angew. Chem., Int. Ed. 2015, 54, 8485−8489. (g) Meng, X.; Yang, B.; Zhang, L.; Pan, G.; Zhang, X.; Shao, Z. Rh(II)/Brønsted Acid Catalyzed General and Highly Diastereo- and Enantioselective Propargylation of in Situ Generated Oxonium Ylides and C-Alkynyl N-Boc N,O-Acetals: Synthesis of Polyfunctional Propargylamines. Org. Lett. 2019, 21, 1292−1296. (h) Yuan, W.; Eriksson, L.; Szabó, K. J. Rhodium Catalyzed Geminal Oxyfluorination and Oxytrifluoro-Methylation of Diazocarbonyl Compounds. Angew. Chem., Int. Ed. 2016, 55, 8410− 8415. (i) Alamsetti, S. K.; Spanka, M.; Schneider, C. Synergistic Rhodium/Phosphoric Acid Catalysis for the Enantioselective Addition of Oxonium Ylides to ortho-Quinone Methides. Angew. Chem., Int. Ed. 2016, 55, 2392−2396. (11) (a) Ma, C.; Xing, D.; Zhai, C.; Che, J.; Liu, S.; Wang, J.; Hu, W. Iron Porphyrin-Catalyzed Three-Component Reaction of Ethyl Diazoacetate with Aliphatic Amines and β,γ-Unsaturated α-Keto Esters. Org. Lett. 2013, 15, 6140−6143. (b) Jing, C.; Xing, D.; Hu, W. Highly diastereoselective synthesis of 3-hydroxy-2,2,3-trisubstituted indolines via intramolecular trapping of ammonium ylides with E
DOI: 10.1021/acs.orglett.9b01207 Org. Lett. XXXX, XXX, XXX−XXX
