Selective Synthesis of 3-Methylene-2,3-dihydrofurans or 1,2,4-Trisubstituted Furans via Tandem Reactions of Allenic Ketones with α-Chloro β-Keto Esters or Ketones

Qiang Wang; Lei Yang; Xuesen Fan

doi:10.1055/s-0033-1340671

Synlett, Inhaltsverzeichnis

Synlett 2014; 25(5): 687-692
DOI: 10.1055/s-0033-1340671

letter

Selective Synthesis of 3-Methylene-2,3-dihydrofurans or 1,2,4-Trisubstituted Furans via Tandem Reactions of Allenic Ketones with α-Chloro β-Keto Esters or Ketones

Qiang Wang

^aSchool of Chemistry and Chemical Engineering, Key Laboratory of Green Chemical Media and Reactions, Ministry of Education, Henan Key Laboratory for Environmental Pollution Control, Henan Normal University, Xinxiang 453007, P. R. of China Fax: +86(373)3326336 eMail: xuesen.fan@htu.cn

^bSchool of Physics-Chemistry, Henan Polytechnic University, Jiaozuo 454003, P. R. of China

,

Lei Yang

^bSchool of Physics-Chemistry, Henan Polytechnic University, Jiaozuo 454003, P. R. of China

,

Xuesen Fan*

^aSchool of Chemistry and Chemical Engineering, Key Laboratory of Green Chemical Media and Reactions, Ministry of Education, Henan Key Laboratory for Environmental Pollution Control, Henan Normal University, Xinxiang 453007, P. R. of China Fax: +86(373)3326336 eMail: xuesen.fan@htu.cn

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Abstract

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Abstract

Novel and efficient synthesis of functionalized furan derivatives have been developed in this paper. Promoted by K₂CO₃, allenic ketones underwent tandem reactions with 2-chloroacetoacetate or 3-chloropentane-2,4-dione to afford 3-methylene-2,3-dihydrofurans with high efficiency under remarkably mild conditions. When the same substrates were treated with potassium carbonate and triphenylphosphine, on the other hand, 1,2,4-trisubstituted furans could be obtained in good yields.

Key words

allenic ketones - furan derivatives - phosphine catalysis - tandem reactions

Volltext

Referenzen

References and Notes

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5 Typical Procedure for the Preparation of Compounds 3aa–da,na,ab – Exemplified with 3aa (Table 1, Entry 1) To a flask containing 1-phenylbuta-2,3-dien-1-one (1a, 1 mmol) and ethyl 2-chloroacetoacetate (2, 1.1 mmol) in MeCN (3 mL) were added anhydrous K₂CO₃ (1.0 mmol). The solution was stirred at r.t. for 1 h. The reaction then was quenched with aq NH₄Cl and extracted with EtOAc (3 × 5 mL). The combined organic phases were dried, filtered, and concentrated under vacuum. The residue was purified by column chromatography over silica gel using EtOAc–PE (1:15, v/v) as eluent to give 3aa (68%). 2-Acetyl-3-methylene-5-phenyl-2,3-dihydrofuran-2-carboxylate (3aa, Table 1, Entry 1) Eluent: EtOAc–PE (1:15), yellow oil; yield: 85%. ¹H NMR (400 MHz, CDCl₃): δ = 7.71–7.68 (m, 2 H), 7.42–7.38 (m, 3 H), 6.07 (s, 1 H), 5.18 (s, 1 H), 5.12 (s, 1 H), 4.29 (q, J = 6.8 Hz, 2 H), 2.31 (s, 3 H), 1.30 (t, J = 7.2 Hz, 3 H). ¹³C NMR (100 MHz, CDCl₃): δ = 200.0, 166.1, 161.1, 144.7, 129.9, 129.1, 128.8, 128.6, 125.6, 104.9, 101.9, 94.1, 62.5, 25.1, 14.013. ESI-HRMS: m/z calcd for C₁₆H₁₇O₄ [M + H]⁺: 273.1127; found: 273.1137. Ethyl 2-Acetyl-5-(4-bromophenyl)-3-methylene-2,3-dihydrofuran-2-carboxylate (3ba, Table 1, Entry 2) Eluent: EtOAc–PE (1:15); yellow oil; yield: 82%. ¹H NMR (400 MHz, CDCl₃): δ = 7.54–7.53 (m, 4 H), 6.06 (s, 1 H), 5.20 (s, 1 H), 5.14 (s, 1 H), 4.28 (q, J = 7.2 Hz, 2 H), 2.30 (s, 3 H), 1.30 (t, J = 7.2 Hz, 3 H). ¹³C NMR (100 MHz, CDCl₃): δ = 199.7, 166.0, 160.0, 144.3, 131.9, 128.0, 127.1, 124.0, 105.7, 102.5, 94.1, 62.7, 25.1, 14.0. ESI-HRMS: m/z calcd for C₁₆H₁₆BrO₄ [M + H]⁺: 351.0232; found: 351.0237. Ethyl 2-Acetyl-3-methylene-5-p-tolyl-2,3-dihydrofuran-2-carboxylate (3ca, Table 1, Entry 3) Eluent: EtOAc–PE (1:15); yellow oil; yield: 86%. ¹H NMR (400 MHz, CDCl₃): δ = 7.59 (d, J = 8.4 Hz, 2 H), 7.21 (d, J = 8.0 Hz, 2 H), 6.02 (s, 1 H), 5.51 (s, 1 H), 5.08 (s, 1 H), 4.29 (t, J = 6.8 Hz, 2 H), 2.38 (s, 3 H), 2.31 (s, 3 H), 1.30 (t, J = 6.8 Hz, 3 H). ¹³C NMR (100 MHz, CDCl₃): δ = 200.2, 166.2, 161.4, 144.8, 140.2, 129.3, 126.4, 125.6, 104.3, 101.1, 94.0, 62.5, 25.1, 25.5, 14.0. ESI-HRMS: m/z calcd for C₁₇H₁₉O₄ [M + H]⁺: 287.1283; found: 287.1280. Ethyl 2-Acetyl-3-methylene-5-(3-oxo-3-phenylpropyl)-2,3-dihydrofuran-2-carboxylate (3da, Table 1, Entry 4) Eluent: EtOAc–PE (1:15); yellow oil; yield: 81%. ¹H NMR (400 MHz, CDCl₃): δ = 7.31–7.27 (m, 2 H), 7.22–7.20 (m, 3 H), 5.38 (s, 1 H), 4.99 (s, 1 H), 4.95 (s, 1 H), 4.31–4.25 (m, 2 H), 2.96–2.91 (m, 2 H), 2.70–2.66 (m, 2 H), 2.23 (s, 3 H), 1.38 (t, J = 7.6 Hz, 3 H). ¹³C NMR (100 MHz, CDCl₃): δ = 199.6, 166.2, 165.1, 144.6, 140.4, 128.5, 128.4, 128.3, 126.4, 103.1, 102.9, 94.1, 62.5, 32.6, 30.0, 24.9, 14.0. ESI-HRMS: m/z calcd for C₁₉H₂₁O₅ [M + H]⁺: 329.1389; found: 329.1383. 1,1′-(3-Methylene-5-phenyl-2,3-dihydrofuran-2,2-diyl)diethanone (3ab, Table 1, Entry 5) Eluent: EtOAc–PE (1:15); yellow oil; yield: 83%. ¹H NMR (400 MHz, CDCl₃): δ = 7.71–7.69 (m, 2 H), 7.44–7.42 (m, 3 H), 6.08 (s, 1 H), 5.13 (s, 1 H), 5.03 (s, 1 H), 2.31 (s, 3 H). ¹³C NMR (100 MHz, CDCl₃): δ = 199.9, 160.9, 144.0, 130.0, 129.1, 128.8, 128.7, 127.0, 125.4, 104.4, 102.3, 99.0, 25.5. ESI-HRMS: m/z calcd for C₁₅H₁₅O₃ [M + H]⁺: 243.1021; found: 243.1027. 1,1′-(3-Ethylidene-5-phenyl-2,3-dihydrofuran-2,2-diyl)diethanone (3na, Table 1, Entry 6) Eluent: EtOAc–PE (1:15); yellow oil; yield: 54%. ¹H NMR (400 MHz, CDCl₃): δ = 7.71–7.69 (m, 2 H), 7.42–7.36 (m, 3 H), 6.18 (s, 1 H), 5.51 (q, J = 7.6 Hz, 1 H), 4.31–4.23 (m, 2 H), 2.29 (s, 3 H), 1.85 (d, J = 7.2 Hz, 3 H), 1.29 (t, J = 7.6 Hz, 3 H). ¹³C NMR (100 MHz, CDCl₃): δ = 200.8, 166.7, 159.6, 136.9, 129.5, 128.6, 125.4, 116.2, 98.6, 93.8, 62.4, 25.1, 15.4, 14.0. ESI-HRMS: m/z calcd for C₁₆H₁₇O₃ [M + H]⁺: 257.1178; found: 257.1183.

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11 Typical Procedure for the Preparation of Compounds 4aa–ma,jb–kb – Exemplified with 4aa (Table 3, Entry 1) To a flask containing 1-phenylbuta-2,3-dien-1-one (1a, 1 mmol) and triphenylphosphine (0.5 mmol) in toluene (5 mL) were added ethyl 2-chloroacetoacetate (2, 1.1 mmol) and anhydrous K₂CO₃ (1.0 mmol). The solution was stirred at r.t. for 1.5 h. The reaction then was quenched with aq NH₄Cl and extracted with EtOAc (3 × 5 mL). The combined organic phases were dried, filtered, and concentrated under vacuum. The residue was purified by column chromatography over silica gel using EtOAc–PE (1:30, v/v) as eluent to give 4aa (65%). Ethyl 2-Methyl-5-(2-oxo-2-phenylethyl)furan-3-carboxylate (4aa, Table 3, Entry 1) Eluent: EtOAc–PE (1:30); yellow syrup; yield: 65%. ¹H NMR (400 MHz, CDCl₃): δ = 7.98 (d, J = 8.0 Hz, 2 H), 7.57 (t, J = 7.2 Hz, 1 H), 7.46 (t, J = 8.0 Hz, 1 H), 6.49 (s, 1 H), 4.24 (s, 2 H), 4.24 (q, J = 7.6 Hz, 2 H), 2.52 (s, 3 H), 1.30 (t, J = 7.6 Hz, 3 H). ¹³C NMR (100 MHz, CDCl₃): δ = 194.6, 164.0, 158.8, 146.2, 136.0, 133.6, 128.8, 128.5, 114.5, 109.3, 60.1, 38.0, 14.4, 13.8. ESI-HRMS: m/z calcd for C₁₆H₁₇O₄ [M + H]⁺: 273.1127; found: 273.1130. Ethyl 5-[2-(4-Fluorophenyl)-2-oxoethyl]-2-methylfuran-3-carboxylate (4ba, Table 3, Entry 2) Eluent: EtOAc–PE (1:30); yellow solid; yield: 58%. ¹H NMR (400 MHz, CDCl₃): δ = 8.03–8.00 (m, 2 H), 7.313–7.308 (m, 1 H), 7.15–7.11 (m, 2 H), 6.49 (s, 1 H), 4.24 (q, J = 7.6 Hz, 2 H), 4.21 (s, 2 H), 2.52 (s, 3 H), 1.30 (t, J = 7.2 Hz, 3 H). ¹³C NMR (100 MHz, CDCl₃): δ = 193.1, 167.2, 164.7, 164.0, 158.9, 146.0, 133.8, 133.6, 132.4, 132.4, 132.1, 131.3, 131.2, 128.8, 128.6, 128.6, 128.5, 116.0, 115.8, 114.5, 109.4, 60.1, 38.0, 14.4, 13.8. ESI-HRMS: m/z calcd for C₁₆H₁₆FO₄ [M + H]⁺: 291.1033; found: 291.1037. Ethyl 5-[2-(4-Chlorophenyl)-2-oxoethyl]-2-methylfuran-3-carboxylate (4ca, Table 3, Entry 3) Eluent: EtOAc–PE (1:30); yellow solid; yield: 52%. ¹H NMR (400 MHz, CDCl₃): δ = 7.96 (d, J = 8.8 Hz, 2 H), 7.44 (d, J = 8.8 Hz, 2 H), 6.49 (s, 1 H), 4.24 (q, J = 7.2 Hz, 2 H), 4.22 (s, 2 H), 2.52 (s, 3 H), 1.31 (t, J = 6.8 Hz, 3 H). ¹³C NMR (100 MHz, CDCl₃): δ = 193.5, 164.0, 159.0, 145.8, 140.1, 134.3, 123.0, 129.1, 114.5, 109.5, 60.1, 38.1, 14.4, 13.8. ESI-HRMS: m/z calcd for C₁₆H₁₆ClO₄ [M + H]⁺: 307.0737; found: 307.0742. Ethyl 5-[2-(4-Bromophenyl)-2-oxoethyl]-2-methylfuran-3-carboxylate (4da, Table 3, Entry 4) Eluent: EtOAc–PE (1:30); yellow solid; yield: 53%. ¹H NMR (400 MHz, CDCl₃): δ = 7.83 (d, J = 8.4 Hz, 2 H), 7.58 (d, J = 8.4 Hz, 2 H), 6.47 (s, 1 H), 4.23 (q, J = 6.8 Hz, 2 H), 4.20 (s, 2 H), 2.51 (s, 3 H), 1.29 (t, J = 6.8 Hz, 3 H). ¹³C NMR (100 MHz, CDCl₃): δ = 193.6, 163.9, 158.9, 145.8, 134.7, 132.1, 130.1, 128.8, 114.5, 109.5, 60.1, 38.0, 14.4, 13.8. ESI-HRMS: m/z calcd for C₁₆H₁₆BrO₄ [M + H]⁺: 351.0232; found: 351.0237. Ethyl 5-[2-(4-Cyanophenyl)-2-oxoethyl]-2-methylfuran-3-carboxylate (4ea, Table 3, Entry 5) Eluent: EtOAc–PE (1:10); white solid; yield: 40%. ¹H NMR (400 MHz, CDCl₃): δ = 8.08 (d, J = 8.4 Hz, 2 H), 7.79 (d, J = 8.4 Hz, 2 H), 6.51 (s, 1 H), 4.27 (s, 2 H), 4.25 (q, J = 7.2 Hz, 2 H), 2.53 (s, 3 H), 1.32 (t, J = 7.2 Hz, 3 H). ¹³C NMR (100 MHz, CDCl₃): δ = 193.3, 163.9, 159.1, 145.0, 138.9, 132.7, 129.0, 117.8, 116.8, 114.6, 109.8, 60.2, 38.4, 14.4, 13.8. ESI-HRMS: m/z calcd for C₁₇H₁₆NO₄ [M + H]⁺: 298.1079; found: 298.1083. Ethyl 2-Methyl-5-(2-oxo-2-p-tolylethyl)furan-3-carboxylate (4fa, Table 3, Entry 6) Eluent: EtOAc–PE (1:15); white solid; yield: 82%. ¹H NMR (400 MHz, CDCl₃): δ = 7.87 (d, J = 8.2 Hz, 2 H), 7.24 (d, J = 8.0 Hz, 2 H), 6.47 (s, 1 H), 4.23 (q, J = 7.2 Hz, 2 H), 4.20 (s, 2 H), 2.51 (s, 3 H), 2.38 (s, 3 H), 1.29 (t, J = 7.6 Hz, 3 H). ¹³C NMR (100 MHz, CDCl₃): δ = 194.3, 164.1, 158.8, 146.4, 144.5, 133.5, 129.4, 128.7, 114.4, 109.2, 60.0, 37.9, 21.7, 14.4, 13.8. ESI-HRMS: m/z calcd for C₁₇H₁₉O₄ [M + H]⁺: 287.1283; found: 287.1289. Ethyl 5-[2-(4-Methoxyphenyl)-2-oxoethyl]-2-methylfuran-3-carboxylate (4ga, Table 3, Entry 7) Eluent: EtOAc–PE (1:10); white solid; yield: 80%. ¹H NMR (400 MHz, CD₃OD and DMSO-d ₆): δ = 8.07 (d, J = 8.8 Hz, 2 H), 7.09 (d, J = 8.8 Hz, 2 H), 6.53 (s, 1 H), 4.38 (s, 2 H), 4.28 (q, J = 6.8 Hz, 2 H), 3.92 (s, 3 H), 2.55 (s, 3 H), 1.35 (t, J = 6.8 Hz, 3 H). ¹³C NMR (100 MHz, CDCl₃): δ = 193.8, 164.1, 163.8, 158.4, 148.0, 130.9, 129.1, 114.2, 114.0, 108.9, 60.0, 55.2, 37.3, 13.8, 12.3. ESI-HRMS: m/z calcd for C₁₇H₁₉O₅ [M + H]⁺: 303.1232; found: 303.1236. Ethyl 5-[2-(3-Bromophenyl)-2-oxoethyl]-2-methylfuran-3-carboxylate (4ha, Table 3, Entry 8) Eluent: EtOAc–PE (1:30); white solid; yield: 40%. ¹H NMR (400 MHz, CDCl₃): δ = 8.12 (s, 1 H), 7.91 (d, J = 7.6 Hz, 1 H), 7.71 (d, J = 8.4 Hz, 1 H), 7.36 (t, J = 8.4 Hz, 1 H), 6.50 (s, 1 H), 4.26 (q, J = 7.6 Hz, 2 H), 4.23 (s, 2 H), 2.54 (s, 3 H), 1.32 (t, J = 7.6 Hz, 3 H). ¹³C NMR (100 MHz, CDCl₃): δ = 193.3, 164.0, 159.0, 145.5, 137.7, 136.4, 131.6, 130.4, 127.1, 123.1, 114.5, 109.6, 60.1, 38.1, 14.4, 13.8. ESI-HRMS: m/z calcd for C₁₆H₁₆BrO₄ [M + H]⁺: 351.0232; found: 351.0237. Ethyl 2-Methyl-5-(2-oxo-2-m-tolylethyl)furan-3-carboxylate (4ia, Table 3, Entry 9) Eluent: EtOAc–PE (1:15); yellow oil; yield: 74%. ¹H NMR (400 MHz, CDCl₃): δ = 7.79–7.77 (m, 2 H), 7.37–7.26 (m, 2 H), 6.48 (s, 1 H), 4.25 (q, J = 7.2 Hz, 2 H), 4.22 (s, 2 H), 2.53 (s, 3 H), 2.40 (s, 3 H), 1.31 (t, J = 7.6 Hz, 2 H). ¹³C NMR (100 MHz, CDCl₃): δ = 194.7, 164.0, 158.7, 146.3, 138.6, 136.2, 134.3, 129.0, 128.6, 125.8, 114.5, 109.3, 60.0, 38.0, 21.3, 14.3, 13.7. ESI-HRMS: m/z calcd for C₁₇H₁₉O₄ [M + H]⁺: 287.1283; found: 287.1289. Ethyl 5-[2-(2-Methoxyphenyl)-2-oxoethyl]-2-methylfuran-3-carboxylate (4ja, Table 3, Entry 10) Eluent: EtOAc–PE (1:10); white solid, yield 72%. ¹H NMR (400 MHz, CDCl₃): δ = 7.73–7.71 (m, 1 H), 7.47–7.42 (m, 1 H), 6.99–6.93 (m, 2 H), 6.43 (s, 1 H), 4.26 (s, 2 H), 4.23 (q, J = 6.8 Hz, 2 H), 3.89 (s, 3 H), 2.51 (s, 3 H), 1.29 (t, J = 6.8 Hz, 2 H). ¹³C NMR (100 MHz, CDCl₃): δ = 196.5, 164.1, 158.7, 158.4, 147.3, 134.1, 130.8, 127.2, 120.8, 114.3, 111.6, 108.8, 59.9, 55.5, 42.6, 14.3, 13.7. ESI-HRMS: m/z calcd for C₁₇H₁₉O₅: [M + H]⁺: 303.1232; found: 303.1236. Ethyl 2-Methyl-5-(2-oxo-3-phenylpropyl)furan-3-carboxylate (4ka, Table 3, Entry 11) Eluent: EtOAc–PE (1:15); white solid; yield: 83%. ¹H NMR (400 MHz, CDCl₃): δ = 7.33–7.25 (m, 3 H), 7.17–7.15 (m, 2 H), 6.43 (s, 1 H), 4.25 (q, J = 6.8 Hz, 2 H), 3.73 (s, 2 H), 3.67 (s, 2 H), 2.51 (s, 3 H), 1.32 (t, J = 7.2 Hz, 3 H). ¹³C NMR (100 MHz, CDCl₃): δ = 202.8, 163.9, 158.8, 145.9, 133.6, 129.4, 128.8, 127.2, 114.5, 109.4, 60.0, 49.1, 41.2, 14.3, 13.7. ESI-HRMS: m/z calcd for C₁₇H₁₉O₄ [M + H]⁺: 287.1283; found: 287.1288. Ethyl 2-Methyl-5-(2-oxo-4-phenylbutyl)furan-3-carboxylate (4la, Table 3, Entry 12) Eluent: EtOAc–PE (1:15); colorless oil; yield: 88%. ¹H NMR (400 MHz, CDCl₃): δ = 7.29–7.25 (m, 2 H), 7.20–7.15 (m, 3 H), 6.43 (s, 1 H), 4.26 (q, J = 7.2 Hz, 2 H), 2.89 (t, J = 7.2 Hz, 2 H), 2.79 (t, J = 7.2 Hz, 2 H), 2.53 (s, 3 H), 1.33 (t, J = 6.8 Hz, 3 H). ¹³C NMR (100 MHz, CDCl₃): δ = 204.8, 164.0, 158.9, 146.0, 140.7, 133.9, 133.7, 128.5, 128.4, 126.2, 114.5, 109.3, 60.1, 43.5, 42.2, 29.6, 14.4, 13.8. ESI-HRMS: m/z calcd for C₁₈H₂₁O₄ [M + H]⁺: 301.1440; found: 301.1446. Ethyl 5-[2-(Furan-2-yl)-2-oxoethyl]-2-methylfuran-3-carboxylate (4ma, Table 3, Entry 13) Eluent: EtOAc–PE (1:10); yellow solid; yield: 42%. ¹H NMR (400 MHz, CDCl₃): δ = 7.61 (d, J = 1.2 Hz, 1 H), 7.26–7.25 (m, 1 H), 6.56–6.55 (m, 1 H), 6.50 (s, 1 H), 4.25 (q, J = 6.8 Hz, 2 H), 4.10 (s, 2 H), 2.52 (s, 3 H), 1.31 (t, J = 6.8 Hz, 3 H). ¹³C NMR (100 MHz, CDCl₃): δ = 183.5, 164.1, 158.9, 151.9, 147.0, 145.6, 118.3, 114.5, 112.6, 109.4, 60.1, 37.8, 14.4, 13.8. ESI-HRMS: m/z calcd for C₁₄H₁₅O₅ [M + H]⁺: 263.0919; found: 263.0915. 2-(4-Acetyl-5-methylfuran-2-yl)-1-(2-methoxyphenyl)-ethanone (4jb, Table 3, Entry 14) Eluent: EtOAc–PE (1:30); white solid; yield: 40%. ¹H NMR (400 MHz, CDCl₃): δ = 7.78–7.76 (m, 1 H), 7.51–7.47 (m, 1 H), 7.03–6.97 (m, 2 H), 6.43 (s, 1 H), 4.30 (s, 2 H), 3.93 (s, 3 H), 2.54 (s, 3 H), 2.36 (s, 3 H). ¹³C NMR (100 MHz, CDCl₃): δ = 196.6, 194.4, 158.8, 157.8, 147.3, 134.3, 130.9, 126.9, 122.2, 120.9, 111.6, 108.7, 59.9, 55.6, 42.6, 29.2, 14.5. ESI-HRMS: m/z calcd for C₁₆H₁₇O₄ [M + H]⁺: 273.1127; found: 273.1125. 1-(4-Acetyl-5-methylfuran-2-yl)-3-phenylpropan-2-one (4kb, Table 3, Entry 15) Eluent: EtOAc–PE (1:10) yellow oil; yield: 42%. ¹H NMR (400 MHz, CDCl₃): δ = 7.33–7.26 (m, 3 H), 7.18–7.17 (m, 2 H), 6.39 (s, 1 H), 3.76 (s, 2 H), 3.70 (s, 2 H), 2.52 (s, 3 H), 2.36 (s, 3 H). ¹³C NMR (100 MHz, CDCl₃): δ = 203.0, 194.1, 158.1, 145.8, 133.4, 129.5, 128.9, 127.3, 122.3, 109.2, 49.4, 41.0, 29.2, 14.4. ESI-HRMS: m/z calcd for C₁₆H₁₇O₃ [M + H]⁺: 257.1178; found: 257.1184. 1-(4-Acetyl-5-methylfuran-2-yl)-4-phenylbutan-2-one (4lb, Table 3, Entry 16) Eluent: EtOAc–PE (1:10); yellow oil; yield: 44%. ¹H NMR (400 MHz, CDCl₃): δ = 7.29–7.25 (m, 2 H), 7.21–7.15 (m, 3 H), 6.38 (s, 1 H), 3.64 (s, 2 H), 2.90 (t, J = 7.6 Hz, 2 H), 2.81 (t, J = 8.0 Hz, 2 H), 2.53 (s, 3 H), 2.36 (s, 3 H). ¹³C NMR (100 MHz, CDCl₃): δ = 204.7, 194.1, 158.1, 145.9, 140.7, 128.6, 128.4, 126.3, 122.3, 109.1, 43.7, 42.1, 29.6, 29.2, 14.4. ESI-HRMS: m/z calcd for C₁₇H₁₉O₃ [M + H]⁺: 271.1334; found: 271.1341.

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