Subscribe to RSS
DOI: 10.1055/a-2184-4940
Facile Installation of β-Hydroxyarylethylamino Motifs at the C2-Position of Quinoline Moiety via Copper-Catalyzed [3+3]-Cycloaddition Reaction of N-Oxide with N-Ts Aziridine
A.D gratefully acknowledges the Science and Engineering Research Board, Department of Science and Technology (SERB, DST CRG/2022/ 01606), and DST-INSPIRE (IFA-14-CH-135) for the financial support.
Abstract
A general and atom-efficient synthesis of quinoline-C2-substituted β-hydroxyarylethylamino derivatives was achieved by copper-catalyzed [3+3]-cycloaddition reaction of N-oxide with N-Ts aziridines. Notably, temperature has a huge impact on this transformation as evidenced by the fact that, at 80 °C, exclusively the [3+3] cycloadduct was isolated whereas, at elevated temperature (140 °C), it has been converted into the aminated product with good yield. Notably, there is no byproduct in the overall process. The use of base-free conditions, excellent site selectivity, and good functional group tolerance are the important features of the process.
Key words
β-hydroxyarylethylamino motifs - [3+3]-cycloaddition reaction - C–H functionalization - atom economy - one-pot reactionSupporting Information
- Supporting information for this article is available online at https://doi.org/10.1055/a-2184-4940.
- Supporting Information
Publication History
Received: 08 July 2023
Accepted after revision: 29 September 2023
Accepted Manuscript online:
29 September 2023
Article published online:
10 November 2023
© 2023. Thieme. All rights reserved
Georg Thieme Verlag KG
Rüdigerstraße 14, 70469 Stuttgart, Germany
-
References and Notes
- 1a Joule JA, Mills K. In Heterocyclic Chemistry, 5th ed. Wiley-Blackwell; New York: 2010: 249-288
- 1b Kumar S, Bawa S, Gupta H. Mini-Rev. Med. Chem. 2009; 9: 1648
- 1c Hu YQ, Gao C, Zhang S, Xu L, Xu Z, Feng LS, Wu X, Zhao F. Eur. J. Med. Chem. 2017; 139: 22
- 1d Vandekerckhove S, D’hooghe M. Bioorg. Med. Chem. 2015; 23: 5098
- 1e Tao S, Li L, Yu J, Jiang Y, Zhou Y, Lee C.-S, Lee S.-T, Zhang X, Kwon O. Chem. Mater. 2009; 21: 1284
- 1f Michael JP. Nat. Prod. Rep. 2007; 24: 223
- 1g Khan QA, Lu J, Hecht SM. J. Nat. Prod. 2009; 72: 438
- 2a Cinelli MA, Li H, Pensa AV, Kang S, Roman LJ, Martasek P, Poulos TL, Silverman RB. J. Med. Chem. 2015; 58: 8694
- 2b Gao Z.-G, Verzijl D, Zweemer A, Ye K, Göblyös A, Ijzerman AP, Jacobson KA. Biochem. Pharmacol. 2011; 82: 658
- 2c Holden JK, Lewis MC, Cinelli MA, Abdullatif Z, Pensa AV, Silverman RB, Poulos TL. Biochemistry 2016; 55: 5587
- 2d Manley PW, Cowan-Jacob SW, Buchdunger E, Fabbro D, Fendrich G, Furet P, Meyer T, Zimmermann J. Eur. J. Cancer 2002; 38: S19
- 2e Roughley SD, Jordan AM. J. Med. Chem. 2011; 54: 3451
- 2f Matada BS, Pattanashettar R, Yernale NG. Bioorg. Med. Chem. 2021; 32: 115973
- 2g Weyesa A, Mulugeta E. RSC Adv. 2020; 10: 20784
- 3a Venetsanaki V, Karabouta Z, Polyzos SA. Eur. J. Pharmacol. 2019; 863: 172661
- 3b O’Dell TB. Ann. N. Y. Acad. Sci. 1960; 86: 191
- 4a Poe Gray A. DE1420056C3, 1973
- 4b Sripahco T, Khruengsai S, Charoensup R, Tovaranonte J, Pripdeevech P. Sci. Rep. 2022; 12: 2225
- 4c Karaman M, Akkemik E, Budak H, Ciftci M. J. Enzyme Inhib. Med. Chem. 2012; 27: 18
- 5a Kinzel O, Steeneck C, Kremoser C. EP2545964A1, 2013
- 5b Weber E, Younis IR, Nelson C, Ding D, Qin A, Xiao D, Watkins TR, Othman AA. J. Clin. Pharmacol. 2023; 63: 560
- 5c Trauner M, Bowlus CL, Gulamhusein A, Hameed B, Caldwell SH, Shiffman ML, Landis C, Muir AJ, Billin A, Xu J. J. Clin. Gastroenterol. 2023; 21: 1552
- 6a Vazirally S, Yadavalli SK, Changalaraya D, Pachiyappan C. IN202141030661A, 2023
- 6b Datla A, Walavalker PA, Konda A, Trivikram SB. US20100144799A1, 2010
- 6c Alcaide B, Pérez-Ossorio R, Plumet J, Sierra MA. Tetrahedron Lett. 1986; 27: 1627
- 6d Kaczynski TP, Manszewski T, Chmielewski MK. Eur. J. Org. Chem. 2016; 2522
- 6e Chmielewski MK, Tykarska E, Markiewicz WT, Rypniewski W. New J. Chem. 2012; 36: 603
- 7a Wang D, Désaubry L, Li G, Huang M, Zheng S. Adv. Synth. Catal. 2021; 363: 2
- 7b Sarmah BK, Konwar M, Bhattacharyya D, Adhikari P, Das A. Adv. Synth. Catal. 2019; 361: 5616
- 8 Sarmah BK, Konwar M, Das A. J. Org. Chem. 2021; 86: 10762
- 9 Sarmah BK, Konwar M, Das A. Org. Lett. 2021; 23: 8390
- 10a Wani IA, Sayyad M, Ghorai MK. Chem. Commun. 2017; 53: 4386
- 10b Pathipati SR, Singh V, Eriksson L, Selander N. Org. Lett. 2015; 17: 4506
- 10c Kaicharla T, Jacob A, Gonnade RG, Biju AT. Chem. Commun. 2017; 53: 8219
- 10d Cardoso AL, Pinh e Melo TM. V. D. Eur. J. Org. Chem. 2012; 6479
- 10e Stanković S, D’hooghe M, Catak S, Eum H, Waroquier M, Van Speybroeck V, De Kimpe N, Ha H.-J. Chem. Soc. Rev. 2012; 41: 643
- 10f Huang C.-Y, Doyle AG. Chem. Rev. 2014; 114: 8153
- 10g Kok GP. Y, Yang H, Wong MW, Zhao Y. Org. Lett. 2018; 20: 5112
- 10h Tu L, Li Z, Feng T, Yu S, Huang R, Li J, Wang W, Zheng Y, Liu J. J. Org. Chem. 2019; 84: 11161
- 11a Werz DB, Biju AT. Angew. Chem. Int. Ed. 2020; 59: 3385
- 11b Schneider TF, Kaschel J, Werz DB. Angew. Chem. Int. Ed. 2014; 53: 5504
- 11c Reissig H.-U, Zimmer R. Chem. Rev. 2003; 103: 1151
- 11d Kerr MA. Isr. J. Chem. 2016; 56: 476
- 11e Braun CM, Congdon EA, Nolin KA. J. Org. Chem. 2015; 80: 1979
- 12 General Procedure for the Synthesis of Quinoline-C2-substituted β-Hydroxyarylethylamino Derivatives (GP) In an oven-dried Schlenk tube, Cu(OTf)2 (10 mol%), N-oxide 1 (0.5 mmol, 1 equiv.), N-Ts aziridine 2 (0.5 mmol, 1 equiv.), and chlorobenzene (1.5 mL) were taken under argon. The reaction mixture was heated gradually from room temperature to 80 °C for 15 h. After complete consumption of the starting reactants as observed by TLC, the temperature was increased to 140 °C, and the mixture was stirred for another 33 h. Then the volatile portion was removed under vacuum, and the crude product was purified through silica gel column chromatography to obtain the analytically pure product. N-(2-Hydroxy-2-phenylethyl)-N-(6-methoxyquinolin-2-yl)-4-methylbenzenesulfonamide (3a) Following the general procedure, the title compound 3a was isolated as colorless oil using silica gel column chromatography with petroleum ether/ethyl acetate (v/v = 3/2, Rf = 0.4) in 86% yield (193 mg). 1H NMR (400 MHz, chloroform-d): δ = 8.45 (d, J = 2.8 Hz, 1 H), 7.87 (d, J = 9.2 Hz, 1 H), 7.74 (d, J = 8.1 Hz, 2 H), 7.35–7.30 (m, 5 H), 7.22 (d, J = 8.0 Hz, 2 H), 7.17 (dd, J = 9.1, 2.8 Hz, 1 H), 6.99 (d, J = 2.8 Hz, 1 H), 6.79 (d, J = 2.8 Hz, 1 H), 5.30–5.26 (m, 1 H), 5.03–4.99 (m, 1 H), 3.87 (s, 3 H), 3.55–3.49 (m, 1 H), 3.40–3.34 (m, 1 H), 2.32 (s, 3 H). 13C NMR (151 MHz, chloroform-d): δ = 158.5, 143.8, 141.7, 139.8, 137.4 (2 ArC overlap), 137.0, 130.5, 129.9, 129.3 (2 ArC overlap), 128.9, 127.1, 126.2, 119.8, 115.2, 104.8, 79.3, 55.6, 49.6, 21.5. HRMS (ESI): m/z [M + H]+ calcd for C25H25N2O4S: 449.1530; found: 449.1534. N-(2-Hydroxy-2-(p-tolyl)ethyl]-N-(6-methoxyquinolin-2-yl)-4-methylbenzenesulfonamide (3b) Following the general procedure, the title compound 3b was isolated as yellow oil using silica gel column chromatography with petroleum ether/ethyl acetate (v/v = 3/2, Rf = 0.4) in 80% yield (185 mg). 1H NMR (600 MHz, chloroform-d): δ = 8.43 (s, 1 H), 7.85 (d, J = 9.2 Hz, 1 H), 7.73 (d, J = 7.9 Hz, 2 H), 7.21–7.18 (m, 4 H), 7.15–7.12 (m, 3 H), 6.97 (br, 1 H), 6.77 (br, 1 H), 5.63 (m, 1 H), 5.25–5.23 (m, 1 H), 3.85 (s, 3 H), 3.50–3.46 (m, 1 H), 3.37–3.32 (m, 1 H), 2.29 (d, J = 5.2 Hz, 6H). 13C NMR (151 MHz, chloroform-d): δ = 158.4, 151.2, 143.7, 141.8, 139.7, 138.8, 137.4, 134.0, 130.4, 129.9 (2 ArC overlap), 129.8, 127.0, 126.1, 119.7, 115.1, 104.8, 79.1, 55.6, 49.6, 21.5, 21.3. HRMS (ESI): m/z [M + H]+ calcd for C26H27N2O4S: 463.1687; found: 463.1685. N-[2-(4-Chlorophenyl)-2-hydroxyethyl]-N-(6- methoxyquinolin-2-yl)-4-methylbenzenesulfonamide (3c) Following the general procedure, the title compound 3c was isolated as colorless oil using silica gel column chromatography with petroleum ether/ethyl acetate (v/v = 3/2, Rf = 0.45) in 90% yield (217 mg). 1H NMR (400 MHz, chloroform-d): δ = 8.44 (s, 1 H), 7.87 (d, J = 9.2 Hz, 1 H), 7.72 (d, J = 8.4 Hz, 2 H), 7.46 (d, J = 8.4 Hz, 2 H), 7.22–7.16 (m, 5 H), 6.96 (d, J = 2.8 Hz, 1 H), 6.80 (d, J = 2.8 Hz, 1 H), 5.37–5.34 (m, 1 H), 5.29–5.26 (m, 1 H), 3.87 (s, 3 H), 3.52–3.45 (m, 1 H), 3.38–3.31 (m, 1 H), 2.31 (s, 3 H). 13C NMR (151 MHz, chloroform-d): δ = 158.5, 143.8, 141.7, 139.8, 137.4, 137.0, 130.5, 129.9, 129.3 (2 ArC overlap), 128.9, 127.1 (2 ArC overlap), 126.2, 119.8, 115.2, 104.8, 79.3, 55.6, 49.6, 21.5. HRMS (ESI): m/z [M + H]+ calcd for C25H24ClN2O4S: 483.1140; found: 483.1145. N-[2-(4-Bromophenyl)-2-hydroxyethyl]-N-(6-methoxyquinolin-2-yl)-4-methylbenzenesulfonamide (3d) Following the general procedure, the title compound 3d was isolated as yellow sticky oil using silica gel column chromatography with petroleum ether/ethyl acetate (v/v = 3/2, Rf = 0.4) in 92% yield (243 mg). 1H NMR (600 MHz, chloroform-d): δ = 8.44 (s, 1 H), 7.87 (d, J = 9.2 Hz, 1 H), 7.72 (d, J = 7.9 Hz, 2 H), 7.47 (d, J = 8.8 Hz, 2 H), 7.22–7.17 (m, 5 H), 6.96 (d, J = 2.8 Hz, 1 H), 6.80 (d, J = 2.8 Hz, 1 H), 5.28–5.26 (m, 1 H), 5.15–5.13 (m, 1 H), 3.87 (s, 3 H), 3.51–3.47 (m, 1 H), 3.37–3.32 (m, 1 H), 2.32 (s, 3 H). 13C NMR (151 MHz, chloroform-d): δ = 158.6, 150.9, 143.9, 141.5, 140.0, 137.3, 136.1, 132.5, 130.6, 130.0, 127.9, 127.1, 126.6, 123.0, 120.0, 115.2, 104.8, 78.8, 55.7, 49.4, 21.6. HRMS (ESI): m/z [M + H]+ calcd for C25H24BrN2O4S: 527.0635; found: 527.0636. N-[2-Hydroxy-2-(3-methoxyphenyl)ethyl]-N-(6-methoxyquinolin-2-yl)-4-methylbenzenesulfonamide (3e) Following the general procedure, the title compound 3e was isolated as yellow oil using silica gel column chromatography with petroleum ether/ethyl acetate (v/v = 3/2, Rf = 0.4) in 89% yield (213 mg). 1H NMR (600 MHz, chloroform-d): δ = 8.44 (s, 1 H), 7.86 (d, J = 9.1 Hz, 1 H), 7.74 (d, J = 7.9 Hz, 2 H), 7.27–7.24 (m, 1 H), 7.20–7.15 (m, 3 H), 6.99 (d, J = 2.8 Hz, 1 H), 6.92 (d, J = 7.6 Hz, 1 H), 6.85 (s, 1 H), 6.82–6.79 (m, 2 H), 5.42–5.40 (m, 1 H), 5.24–5.22 (m, 1 H), 3.86 (s, 3 H), 3.75 (s, 3 H), 3.53–3.49 (m, 1 H), 3.39–3.34 (m, 1 H), 2.29 (s, 3 H). 13C NMR (151 MHz, chloroform-d): δ = 160.2, 158.4, 151.2, 143.7, 141.7, 139.8, 138.7, 137.4, 130.5, 130.4, 129.9, 129.8, 127.1, 119.8, 118.4, 115.1, 114.0, 111.9, 104.8, 79.2, 55.6, 55.4, 49.6, 21.5. HRMS (ESI): m/z [M + H]+ calcd for C26H27N2O5S: 479.1636; found: 479.1637. N-[2-(3-Chlorophenyl)-2-hydroxyethyl]-N-(6-methoxyquinolin-2-yl)-4-methylbenzenesulfonamide (3f) Following the general procedure, the title compound 3f was isolated as colorless oil using silica gel column chromatography with petroleum ether/ethyl acetate (v/v = 3/2, Rf = 0.45) in 81% yield (194 mg). 1H NMR (400 MHz, chloroform-d): δ = 8.53 (s, 1 H), 8.11 (s, 1 H), 8.02–7.92 (m, 1 H), 7.75 (d, J = 7.9 Hz, 2 H), 7.54 (d, J = 10.0 Hz, 1 H), 7.40 (t, J = 7.8 Hz, 1 H), 7.33 (s, 1 H), 7.26–7.25 (m, 1 H), 7.18 (d, J = 7.9 Hz, 2 H), 7.05 (s, 1 H), 6.81 (s, 1 H), 6.03 (s, 1 H), 5.34–5.31 (m, 1 H), 3.86 (s, 3 H), 3.50–3.47 (m, 1 H), 3.39–3.34 (m, 1 H), 2.28 (s, 3 H). 13C NMR (151 MHz, chloroform-d): δ = 158.7, 143.7, 139.2, 137.3, 135.2, 134.6, 133.1, 130.6, 130.2, 129.9, 129.8, 129.1, 128.2, 127.0, 126.3, 124.5, 120.6, 116.2, 104.8, 79.0, 55.7, 49.5, 21.5. HRMS (ESI): m/z [M + H]+ calcd for C25H24ClN2O4S: 483.1140; found: 483.1143. N-[2-(3-Bromophenyl)-2-hydroxyethyl]-N-(6-methoxyquinolin-2-yl)-4-methylbenzenesulfonamide (3g) Following the general procedure, the title compound 3g was isolated as yellow sticky oil using silica gel column chromatography with petroleum ether/ethyl acetate (v/v = 3/2, Rf = 0.4) in 89% yield (234 mg). 1H NMR (600 MHz, chloroform-d): δ = 8.46 (s, 1 H), 7.87 (d, J = 9.1 Hz, 1 H), 7.73 (d, J = 7.9 Hz, 2 H), 7.47 (s, 1 H), 7.43 (d, J = 8.0 Hz, 1 H), 7.28 (d, J = 7.7 Hz, 1 H), 7.23–7.17 (m, 4 H), 6.95 (s, 1 H), 6.81 (s, 1 H), 5.43–5.41 (m, 1 H), 5.26–5.24 (m, 1 H), 3.87 (s, 3 H), 3.52–3.48 (m, 1 H), 3.35–3.30 (m, 1 H), 2.29 (s, 3 H). 13C NMR (151 MHz, chloroform-d): δ = 158.5, 150.9, 143.9, 141.5, 139.8, 139.4, 137.2, 132.1, 130.9, 130.4, 130.0, 129.7, 129.1, 127.0, 124.9, 123.4, 120.1, 115.0, 104.7, 78.5, 55.7, 49.5, 21.6. HRMS (ESI): m/z [M + H]+ calcd for C25H24BrN2O4S: 527.0635; found: 527.0654. N-(6-Ethoxyquinolin-2-yl)-N-(2-hydroxy-2-phenylethyl)-4-methylbenzenesulfonamide (3i) Following the general procedure, the title compound 3j was isolated as yellow sticky oil using silica gel column chromatography with petroleum ether/ethyl acetate (v/v = 3/2, Rf = 0.4) in 74% yield (171 mg). 1H NMR (400 MHz, chloroform-d): δ = 8.45 (s, 1 H), 7.87 (d, J = 9.3 Hz, 1 H), 7.74 (d, J = 8.3 Hz, 2 H), 7.34–7.33 (m, 4 H), 7.21–7.14 (m, 4 H), 6.98 (d, J = 2.7 Hz, 1 H), 6.77 (d, J = 2.7 Hz, 1 H), 5.38 (br, 1 H), 5.30–5.27 (m, 1 H), 4.09–4.06 (m, 2 H), 3.53–3.49 (m, 1 H), 3.40–3.34 (m, 1 H), 2.30 (s, 3 H), 1.45 (t, J = 7.0 Hz, 3 H). 13C NMR (151 MHz, chloroform-d): δ = 157.9, 143.8, 141.5, 139.6, 137.4, 137.1, 130.2, 129.9, 129.6, 129.2, 128.9, 127.1, 126.5, 126.2, 120.2, 115.4, 105.5, 79.3, 63.9, 49.6, 21.5, 14.9. HRMS (ESI): m/z [M + H]+ calcd for C26H27N2O4S: 463.1687; found: 463.1689. N-[6-(Benzyloxy)quinolin-2-yl]-N-(2-hydroxy-2-phenylethyl)-4-methylbenzenesulfonamide (3j) Following the general procedure, the title compound 3k was isolated as yellow oil using silica gel column chromatography with petroleum ether/ethyl acetate (v/v = 3/2, Rf = 0.4) in 90% yield (236 mg). 1H NMR (400 MHz, chloroform-d): δ = 8.45 (s, 1 H), 7.88 (d, J = 9.1 Hz, 1 H), 7.73 (d, J = 8.0 Hz, 2 H), 7.44–7.43 (m, 2 H), 7.40–7.37 (m, 3 H), 7.32–7.31 (m, 5 H), 7.26–7.24 (m, 1 H), 7.15 (d, J = 7.9 Hz, 2 H), 6.98 (d, J = 2.8 Hz, 1 H), 6.87 (d, J = 2.8 Hz, 1 H), 5.78 (br, 1 H), 5.29 (dd, J = 8.9, 3.6 Hz, 1 H), 5.08 (s, 2 H), 3.54–3.47 (m, 1 H), 3.40–3.34 (m, 1 H), 2.24 (s, 3 H). 13C NMR (151 MHz, chloroform-d): δ = 157.5, 151.2, 143.6, 141.8, 139.6, 137.4, 137.0, 136.5, 130.3, 129.84, 129.77, 129.2, 128.9, 128.8, 128.3, 127.6, 127.0, 126.2, 120.1, 115.2, 106.1, 79.3, 70.3, 49.6, 21.5. HRMS (ESI): m/z [M + H]+ calcd for C31H29N2O4S: 525.1843; found: 525.1848. N-(2-Hydroxy-2-phenylethyl)-4-methyl-N-[6-(p-tolyloxy)quinolin-2-yl]benzenesulfonamide (3k) Following the general procedure, the title compound 3k was isolated as yellow oil using silica gel column chromatography with petroleum ether/ethyl acetate (v/v = 3/2, Rf = 0.4) in 84% yield (220 mg). 1H NMR (400 MHz, chloroform-d): δ = 8.52 (s, 1 H), 7.95 (d, J = 9.1 Hz, 1 H), 7.73 (d, J = 8.2 Hz, 2 H), 7.31–7.27 (m, 6 H), 7.18 (dd, J = 8.1, 5.7 Hz, 4 H), 6.94 (d, J = 8.4 Hz, 2 H), 6.88–6.86 (m, 2 H), 5.30 (dd, J = 8.9, 4.2 Hz, 1 H), 5.22 (dd, J = 8.9, 3.8 Hz, 1 H), 3.53–3.47 (m, 1 H), 3.39–3.32 (m, 1 H), 2.36 (s, 3 H), 2.29 (s, 3 H). 13C NMR (151 MHz, chloroform-d): δ = 157.0, 154.0, 143.8, 142.8, 137.4, 136.8, 133.9, 130.7, 130.6, 129.9, 129.3, 129.0, 128.5 (2 ArC overlap), 127.1 (2 ArC overlap), 126.2, 120.6, 119.9, 115.1, 111.4, 79.2, 49.6, 21.5, 20.9. HRMS (ESI): m/z [M + H]+ calcd for C31H29N2O4S: 525.1843; found: 525.1841. 8-Methoxy-2-phenyl-4-tosyl-2,3,4,4a-tetrahydro-[1,2,4]oxadiazino[2,3-a]quinoline (3a′) In an oven-dried Schlenk tube, Cu(OTf)2 (10 mol%), N-oxide 1 (0.5 mmol, 1 equiv.), N-Ts aziridine 2 (0.5 mmol, 1 equiv.), and chlorobenzene (1.5 mL) were taken under argon. The reaction mixture was heated gradually from room temperature to 80 °C for 15 h. After complete consumption of the starting reactants as observed by TLC, the volatile portion was removed under vacuum, and the crude product was purified through silica gel column chromatography to obtain the analytically pure product. The compound was purified through SiO2 gel column chromatography with petroleum ether/ethyl acetate (v/v = 7/3, Rf = 0.6) in 84% yield (150 mg). 1H NMR analysis showed a dr of 2:1, as determined by the following signals: δ = 3.92 (s, 3 H, OCH3) major, 3.89 (s, 3 H, OCH3) minor. 1H NMR (400 MHz, chloroform-d): δ = 8.03 (d, J = 8.9 Hz, 1 H, major, 66%), 7.88 (d, J = 8.8 Hz, 1 H, minor, 33%), 7.82 (d, J = 9.2 Hz, 1 H, major, 66%), 7.78 (d, J = 8.9 Hz, 1 H, major, 66%), 7.69–7.65 (m, 3 H, major 66% + m, 1 H, minor, 33%), 7.49 (d, J = 7.4 Hz, 2 H, major, 66%), 7.37–7.35 (m, 3 H, major 66% + m, 1 H, minor, 33%), 7.33–7.28 (m, 4 H, minor, 33%), 7.25–7.23 (m, 1 H, major 66% + m, 1 H, minor, 33%), 7.23–7.18 (m, 4 H, minor, 33%), 7.07 (d, J = 2.7 Hz, 1 H, major, 66%), 7.02 (d, J = 2.7 Hz, 1 H, minor, 33%), 6.83 (d, J = 8.8 Hz, 1 H, minor, 33%), 6.18 (dd, J = 8.0, 4.0 Hz, 1 H, minor, 33%), 6.02 (s, 1 H, major 66%), 5.83–5.76 (m, 1 H, minor, 33%), 5.12 (d, J = 7.7 Hz, 1 H, major 66%), 4.37 (dd, J = 14.9, 2.4 Hz, 1 H, major 66%), 4.02–3.93 (m, 1 H, major 66% + m, 1 H, minor, 33%), 3.92 (s, 3 H, OCH3, major, 66%), 3.89 (s, 3 H, OCH3, minor, 33%), 3.55 (m, 1 H, major 66% + m, 1 H, minor, 33%), 2.36 (s, 3 H, CH3, major, 66%), 2.35 (s, 3 H, CH3, minor, 33%). 13C NMR (151 MHz, chloroform-d): δ = 159.6, 158.0, 156.6, 150.5, 144.3, 143.4, 142.2, 141.8, 141.5, 138.7, 138.4, 137.4, 137.2, 136.5, 130.0, 129.9, 129.8, 129.3, 128.7, 128.5, 128.4, 128.3, 127.7, 127.5, 127.5, 127.3, 127.2, 126.8, 126.6, 126.2, 126.0, 123.0, 121.6, 118.9, 113.1, 106.2, 105.3, 75.6, 72.8, 58.0, 55.8, 55.7, 49.0, 21.7, 21.6. HRMS (ESI): m/z [M + H]+ calcd for C25H25N2O4S: 449.1530; found: 449.1536.
- 13 Considering HOMO of N-oxide and LUMO of aziridine take part in the cycloaddition reaction.