Ru-Catalyzed Selective C–H Functionalization of Pyridotriazoles with Acrylates

Abhisek Joshi; Rashmi Semwal; Subbarayappa Adimurthy

doi:10.1055/a-1661-5655

SynOpen, Inhaltsverzeichnis

CC BY-NC-ND 4.0 · SynOpen 2021; 05(04): 294-300
DOI: 10.1055/a-1661-5655

letter

Ru-Catalyzed Selective C–H Functionalization of Pyridotriazoles with Acrylates

Abhisek Joshi

,

Rashmi Semwal

,

Subbarayappa Adimurthy ∗

Abstract

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Abstract

Ruthenium-catalyzed efficient and selective C–H alkenylation of pyridotriazoles with acrylates is described. The combination of metals (Ru and Fe) plays a crucial role in achieving quantitative yields of the desired products. The reaction is proposed to involve the formation of a ruthenium cyclometalated intermediate.

Key words

C–H functionalization - pyridotriazoles - acrylates

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Referenzen

References and Notes

For reviews, see:

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10 Experimental SectionAll commercially available chemicals and reagents were used without any further purification unless otherwise indicated. ¹H and ¹³C NMR spectra were recorded at 600, 200, 150, and 125 MHz, respectively. Spectra were recorded in CDCl₃ as solvent. Multiplicity is indicated as follows: s (singlet), d (doublet), t (triplet), m (multiplet), dd (doublet of doublets), and coupling constants (J) are given in Hz. Chemical shifts are reported in ppm relative to TMS as an internal standard. Mass spectra were obtained using electron impact (EI) ionization. Progress of the reactions was monitored by thin-layer chromatography (TLC). All products were purified through column chromatography using silica gel with 100–200 mesh size using ethyl acetate/hexane as eluent unless otherwise stated.General Procedures(A) Synthesis of Triazolopyridine Derivatives 1Hydrazine monohydrate (0.30 mmol) and acetic acid (0.02 mmol) were added to a solution of the requisite 2-acylpyridine (0.20 mmol) in ethanol (1.0 mL) at room temperature. The reaction mixture was heated at reflux for 6 h, and then EtOAc (5.0 mL) and Cu(OAc)₂ (0.01 mmol) were added. After stirring at the indicated temperature for the indicated time, the resulting mixture was cooled to room temperature and then diluted with EtOAc (20 mL). The organic phase was washed with water (10 mL) and then dried over anhydrous Na₂SO₄. After filtration and concentration under reduced pressure, followed by purification by column chromatography, the desired triazolopyridine derivatives were isolated.(B) Synthesis of Methyl (E)-3-(2-{[1,2,3]Triazolo[1,5-a]pyridin-3-yl}phenyl)acrylate (3a)To a reaction tube equipped with a magnetic stir bar, 3-phenyl[1,2,3]triazolo[1,5-a]pyridine (1a, 48.8 mg, 0.25 mmol), methyl acrylate (2a, 43.1 mg, 0.5 mmol), [RuCl₂(p-cymene)]₂ (6.75 mg, 5 mol%), FeCl₃ (81.1 mg, 0.5 mmol), and base KOAc (24.5 mg, 0.25 mmol) were added, followed by dry 1,4-dioxane (1 mL). The mixture was heated in a carousel reaction station at 140 °C in a closed tube for 48 h, and progress was monitored by TLC. After completion of reaction, it was allowed to cool to room temperature. Then the mixture was poured into brine (30 mL). The product was extracted with EtOAc (3 × 15 mL) and dried with anhydrous Na₂SO₄. After filtration and removal of solvent under reduced pressure the residue was purified by column chromatography using silica gel (20% EtOAc/hexane) to afford 3a (62.8 mg, 90% yield).Characterization Data Methyl (E)-3-(2-{[1,2,3]Triazolo[1,5-a]pyridin-3-yl}phenyl)acrylate (3a)Yield (62.8 mg, 90% yield, semisolid), eluent 25% ethyl acetate/hexane. ¹H NMR (600 MHz, CDCl₃): δ = 8.80 (d, J = 7.2 Hz, 1 H), 7.89 (d, J = 16.0 Hz, 1 H), 7.81 (d, J = 7.7 Hz, 1 H), 7.66–7.64 (m, 2 H), 7.53 (t, J = 7.4 Hz, 1 H), 7.49 (d, J = 7.2 Hz, 1 H), 7.31–7.27 (m, 1 H), 7.06 (t, J = 6.8 Hz, 1 H), 6.51 (d, J = 16.0 Hz, 1 H), 3.73 (s, 3 H). ¹³C NMR (150 MHz, CDCl₃): δ = 167.1, 143.2, 136.6, 133.4, 132.0, 131.2, 130.8, 130.1, 128.7, 127.1, 125.8, 125.5, 119.3, 118.1, 115.5, 51.6. ESI-HRMS: m/z [M + Na]⁺ calcd for C₁₉H₁₅NONa: 302.0900; found: 302.0898.Ethyl (E)-3-(2-{[1,2,3]Triazolo[1,5-a]pyridin-3-yl}phenyl)acrylate (3b)Yield (52.8 mg, 72% yield, semisolid), eluent 20% ethyl acetate/hexane. ¹H NMR (600 MHz, CDCl₃): δ = 8.79 (dd, J = 6.9, 2.7 Hz, 1 H), 7.85 (d, J = 16.0 Hz, 1 H), 7.80 (d, J = 7.7 Hz, 1 H), 7.66 (dd, J = 15.4, 8.1 Hz, 2 H), 7.52–7.49 (m, 1 H), 7.47 (t, J = 7.4 Hz, 1 H), 7.28 (d, J = 6.9 Hz, 1 H), 7.03 (t, J = 6.9 Hz, 1 H), 6.49 (d, J = 15.4 Hz, 1 H), 4.19–4.15 (m, 2 H), 1.25 (td, J = 6.9, 1.9 Hz, 3 H). ¹³C NMR (150 MHz, CDCl₃): δ = 166.6, 143.0, 136.6, 133.4, 132.0, 131.2, 130.8, 130.1, 128.7, 127.1, 125.8, 125.5, 119.8, 118.1, 115.4, 60.4, 14.2. ESI-HRMS: m/z [M + Na]⁺ calcd for C₁₇H₁₅N₃O₂Na: 316.1056; found: 316.1056.Butyl (E)-3-(2-{[1,2,3]Triazolo[1,5-a]pyridin-3-yl}phenyl)acrylate (3c)Yield (69.1 mg, 86% yield, semisolid), eluent 20% ethyl acetate/hexane. ¹H NMR (600 MHz, CDCl₃): δ = 8.79 (d, J = 7.1 Hz, 1 H), 7.83–7.79 (m, 2 H), 7.67 (d, J = 7.3 Hz, 1 H), 7.63 (d, J = 8.9 Hz, 1 H), 7.53–7.450 (m, 1 H), 7.48 (t, J = 7.5 Hz, 1 H), 7.29–7.26 (m, 1 H), 7.04 (q, J = 7.1 Hz, 1 H), 6.50 (d, J = 15.9 Hz, 1 H), 4.13 (t, J = 6.5 Hz, 2 H), 1.61–1.55 (m, 2 H), 1.34–1.24 (m, 2 H), 0.91–0.86 (m, 3 H). ¹³C NMR (150 MHz, CDCl₃): δ = 166.7, 142.9, 142.2, 136.6, 133.4, 132.0, 131.2, 130.9, 130.1, 128.7, 128.1, 127.0, 125.8, 125.5, 120.7, 119.8, 118.1, 115.4, 64.3, 30.6, 19.1, 19.0, 13.7. GC–MS: m/z [M] calcd for C₁₉H₁₉N₃O₂: 321.1477; found: 321.00.Methyl (E)-3-(2-{[1,2,3]Triazolo[1,5-a]pyridin-3-yl}phenyl)-2-methylacrylate (3d)Yield (63.8 mg, 87% yield, semisolid), eluent 25% ethyl acetate/hexane. ¹H NMR (600 MHz, CDCl₃): δ = 8.76 (d, J = 7.1 Hz, 1 H), 7.71–7.70 (m, 1 H), 7.63 (s, 1 H), 7.55 (d, J = 8.7 Hz, 1 H), 7.50–7.46 (m, 3 H), 7.25–7.22 (m, 1 H), 7.01 (t, J = 6.7 Hz, 1 H), 3.68 (s, 3 H), 2.06 (s, 3 H). ¹³C NMR (150 MHz, CDCl₃): δ = 167.1, 166.7, 143.7, 143.6, 141.0, 134.8, 133.9, 130.8, 130.7, 130.5, 129.8, 129.2, 129.1, 128.4, 127.9, 124.0, 122.9, 120.4, 112.8, 52.5, 29.8. GC–MS: m/z [M] calcd for C₁₇H₁₅N₃O₂: 293.1164; found: 293.10.2-Methoxyethyl (E)-3-(2-{[1,2,3]Triazolo[1,5-a]pyridin-3-yl}phenyl)acrylate (3e)Yield (65.5 mg, 81% yield, semisolid), eluent 25% ethyl acetate/hexane. ¹H NMR (600 MHz, CDCl₃): δ = 8.83 (d, J = 7.0 Hz, 1 H), 7.84 (s, 1 H), 7.82–7.80 (m, 2 H), 7.65 (d, J = 8.5 Hz, 2 H), 7.53 (dd, J = 8.2, 1.8 Hz, 1 H), 7.36–7.32 (m, 1 H), 7.10 (t, J = 6.7 Hz, 1 H), 6.60 (d, J = 15.9 Hz, 1 H), 4.34–4.32 (m, 2 H), 3.65–3.63 (m, 2 H), 3.41 (s, 3 H). ¹³C NMR (150 MHz, CDCl₃): δ = 166.4, 142.4, 135.7, 135.1, 135.0, 132.2, 130.3, 129.8, 127.2, 126.3, 125.7, 120.7, 118.0, 115.7, 70.5, 63.8, 59.1. GC–MS: m/z [M] calcd for C₁₈H₁₇N₃O₃: 323.1270; found: 323.00.2-Hydroxyethyl (E)-3-(2-{[1,2,3]triazolo[1,5-a]pyridin-3-yl}phenyl)but-2-enoate (3f)Yield (56.6 mg, 70% yield, semisolid), eluent 50% ethyl acetate/hexane. ¹H NMR (600 MHz, CDCl₃): δ = 8.76 (s, 1 H), 7.76 (d, J = 41.3 Hz, 2 H), 7.60 (s, 1 H), 7.51–7.48 (m, 3 H), 7.26 (s, 2 H), 7.01 (s, 1 H), 4.24 (s, 2 H), 3.78 (s, 2 H), 2.07 (s, 3 H). ¹³C NMR (150 MHz, CDCl₃): δ = 168.7, 139.2, 137.2, 134.7, 131.8, 130.8, 130.2, 128.8, 128.5, 128.1, 125.6, 118.4, 115.5, 66.6, 61.4, 14.2. GC–MS: m/z [M] calcd for C₁₈H₁₇N₃O₃: 323.1270; found: 323.00.2,2,2-Trifluoroethyl (E)-3-(2-{[1,2,3]Triazolo[1,5-a]pyridin-3-yl}phenyl)acrylate (3g)Yield (78.0 mg, 90% yield, semisolid), eluent 10% ethyl acetate/hexane. ¹H NMR (600 MHz, CDCl₃): δ = 8.80 (d, J = 7.1 Hz, 1 H), 8.02 (d, J = 15.9 Hz, 1 H), 7.83 (d, J = 7.9 Hz, 1 H), 7.69 (d, J = 7.8 Hz, 1 H), 7.65 (d, J = 8.9 Hz, 1 H), 7.55 (t, J = 7.7 Hz, 1 H), 7.49 (d, J = 7.6 Hz, 1 H), 7.31–7.28 (m, 1 H), 7.06 (t, J = 6.8 Hz, 1 H), 6.56 (d, J = 16.0 Hz, 1 H), 4.55 (q, J = 8.2 Hz, 2 H). ¹³C NMR (150 MHz, CDCl₃): δ = 165.0, 164.2, 146.9, 145.8, 136.4, 132.9, 132.1, 131.7, 130.8, 130.3, 129.6, 129.4, 129.1, 128.9, 128.0, 127.4, 126.7, 126.2, 125.7, 125.7, 125.6, 125.5, 124.0, 122.2, 118.5, 118.2, 118.0, 117.4, 115.6, 115.6, 60.7, 60.4, 60.2, 60.0. GC–MS: m/z [M] calcd for C₁₇H₁₂F₃N₃O₂: 347.0882; found: 347.00.(E)-3-(2-{[1,2,3]Triazolo[1,5-a]pyridin-3-yl}phenyl)acrylonitrile (3h)Yield (56.0 mg, 91% yield, semisolid), eluent 30% ethyl acetate/hexane. ¹H NMR (600 MHz, CDCl₃): δ = 8.82 (d, J = 7.0 Hz, 1 H), 7.77 (d, J = 16.8 Hz, 1 H), 7.72 (d, J = 7.8 Hz, 1 H), 7.69 (d, J = 8.7 Hz, 1 H), 7.64 (d, J = 7.6 Hz, 1 H), 7.57 (t, J = 7.5 Hz, 1 H), 7.50 (t, J = 7.5 Hz, 1 H), 7.36–7.33 (m, 1 H), 7.09 (t, J = 6.9 Hz, 1 H), 5.94 (d, J = 17.0 Hz, 1 H). ¹³C NMR (150 MHz, CDCl₃): δ = 149.3, 136.1, 132.7, 132.0, 131.0, 130.8, 130.6, 130.6, 128.8, 126.5, 126.3, 125.6, 118.1, 117.7, 115.7, 97.5. GC–MS: m/z [M] calcd for C₁₅H₁₀N₄: 246.0905; found: 246.20.2-Ethylhexyl (E)-3-(2-{[1,2,3]Triazolo[1,5-a]pyridin-3-yl}phenyl)acrylate (3i)Yield (60.6 mg, 67% yield, yellow liquid), eluent 15% ethyl acetate/hexane. ¹H NMR (600 MHz, CDCl₃): δ = 8.80–8.79 (m, 1 H), 7.78–7.72 (m, 2 H), 7.62 (t, J = 8.7 Hz, 2 H), 7.49 (dd, J = 8.1, 2.3 Hz, 1 H), 7.31–7.29 (m, 1 H), 7.06 (t, J = 6.5 Hz, 1 H), 6.51 (d, J = 16.1 Hz, 1 H), 4.07 (qd, J = 10.9, 5.7 Hz, 2 H), 1.56 (t, J = 6.0 Hz, 1 H), 1.31–1.24 (m, 11 H), 0.88–0.83 (m, 8 H). ¹³C NMR (150 MHz, CDCl₃): δ = 166.6, 141.6, 135.7, 135.1, 134.9, 132.2, 132.1, 130.2, 129.8, 127.1, 126.2, 125.7, 121.1, 118.0, 115.6, 67.1, 38.8, 30.4, 29.0, 23.8, 23.0, 14.1, 11.1. GC–MS: m/z [M] calcd for C₂₃H₂₇N₃O₂: 377.2103; found: 377.30.Methyl (E)-3-(2-{[1,2,3]Triazolo[1,5-a]pyridin-3-yl}-5-chlorophenyl)acrylate (4a)Yield (65.1 mg, 83% yield, semisolid), eluent 25% ethyl acetate/hexane). ¹H NMR (600 MHz, CDCl₃): δ = 8.80 (d, J = 7.0 Hz, 1 H), 7.81–7.76 (m, 2 H), 7.61–7.58 (m, 2 H), 7.49 (d, J = 8.1 Hz, 1 H), 7.32–7.30 (t, J = 6.0 Hz, 1 H), 7.06 (d, J = 6.8 Hz, 1 H), 6.50 (d, J = 16.1 Hz, 1 H), 3.73 (s, 3 H). ¹³C NMR (150 MHz, CDCl₃): δ = 166.7, 141.9, 135.5, 135.0, 134.8, 132.0, 130.1, 129.6, 127.1, 126.2, 125.6, 120.5, 117.8, 115.6, 51.8. GC–MS: m/z [M] calcd for C₁₆H₁₂ClN₃O₂: 313.0618; found: 313.00.Ethyl (E)-3-(2-{[1,2,3]Triazolo[1,5-a]pyridin-3-yl}-5-chlorophenyl)acrylate (4b)Yield (61.3 mg, 75% yield, semisolid), eluent 20% ethyl acetate/hexane. ¹H NMR (600 MHz, CDCl₃): δ = 8.77 (s, 1 H), 7.84–7.79 (m, 2 H), 7.65 (s, 2 H), 7.50–7.46 (m, 2 H), 7.27 (s, 1 H), 7.02 (s, 1 H), 6.49 (d, J = 15.7 Hz, 1 H), 4.17 (s, 2 H), 1.24 (s, 3 H). ¹³C NMR (150 MHz, CDCl₃): δ = 166.8, 143.1, 136.7, 133.6, 132.2, 131.4, 131.0, 130.2, 128.9, 127.2, 125.9, 125.6, 120.0, 118.3, 115.6, 60.5, 14.4. ESI-HRMS: m/z [M + Na]⁺ calcd for C₁₇H₁₄ClN₃O₂Na: 350.0667; found: 350.0632.Butyl (E)-3-(2-{[1,2,3]Triazolo[1,5-a]pyridin-3-yl}-5-chlorophenyl)acrylate (4c)Yield (76.5 mg, 86% yield, semisolid), eluent 20% ethyl acetate/hexane. ¹H NMR (600 MHz, CDCl₃): δ = 8.80 (d, J = 7.1 Hz, 1 H), 7.82 (d, J = 7.8 Hz, 1 H), 7.68 (d, J = 7.3 Hz, 1 H), 7.64 (d, J = 8.9 Hz, 1 H), 7.54 (t, J = 7.4 Hz, 1 H), 7.49 (t, J = 7.5 Hz, 1 H), 7.30–7.27 (m, 1 H), 7.05 (t, J = 6.8 Hz, 1 H), 6.51 (d, J = 15.9 Hz, 1 H), 4.14 (t, J = 6.5 Hz, 2 H), 1.62–1.58 (m, 2 H), 1.36–1.33 (m, 2 H), 0.92–0.88 (m, 3 H). ¹³C NMR (150 MHz, CDCl₃): δ = 160.0, 159.3, 156.9, 143.9, 138.1, 136.8, 136.2, 130.2, 129.1, 127.6, 122.3, 120.9, 120.5, 114.9, 114.4, 114.3, 113.9, 112.1, 105.4, 55.3, 32.4, 31.2, 30.3. GC–MS: m/z [M] calcd for C₁₉H₁₈ClN₃O₂: 355.1058; found: 355.10.Methyl (E)-3-(2-{[1,2,3]Triazolo[1,5-a]pyridin-3-yl}-5-chlorophenyl)-2-methylacrylate (4d)Yield (67.2 mg, 82% yield, semisolid), eluent 25% ethyl acetate/hexane. ¹H NMR (600 MHz, CDCl₃): δ = 8.77 (d, J = 7.1 Hz, 1 H), 7.72–7.70 (m, 1 H), 7.64 (s, 1 H), 7.56 (d, J = 8.7 Hz, 1 H), 7.51–7.49 (m, 1 H), 7.48 (d, J = 3.3 Hz, 1 H), 7.25 (t, J = 7.32 Hz, 1 H), 7.02 (t, J = 6.7 Hz, 1 H), 3.69 (s, 3 H), 2.07 (s, 3 H). ¹³C NMR (150 MHz, CDCl₃): δ = 160.0, 134.8, 131.2, 129.9, 129.0, 128.5, 126.5, 124.8, 124.2, 123.0, 121.7, 121.0, 115.0, 114.3, 109.2, 55.5, 29.7. GCMS: m/z [M] calcd for C₁₇H₁₄ClN₃O₂: 327.0775; found: 327.05.2-Methoxyethyl (E)-3-(2-{[1,2,3]Triazolo[1,5-a]pyridin-3-yl}-5-chlorophenyl)acrylate (4e)Yield (69.8 mg, 78% yield, semisolid), eluent 25% ethyl acetate/hexane. ¹H NMR (600 MHz, CDCl₃): δ = 8.79 (d, J = 7.0 Hz, 1 H), 7.80–7.76 (m, 2 H), 7.60 (d, J = 8.5 Hz, 2 H), 7.49 (dd, J = 8.2, 1.8 Hz, 1 H), 7.32–7.28 (m, 1 H), 7.06 (t, J = 6.7 Hz, 1 H), 6.56 (d, J = 15.9 Hz, 1 H), 4.30–4.28 (m, 2 H), 3.61–3.59 (m, 2 H), 3.37 (s, 3 H). ¹³C NMR (150 MHz, CDCl₃): δ = 166.2, 142.2, 135.5, 134.9, 134.8, 132.0, 130.2, 129.7, 127.1, 126.2, 125.6, 120.5, 117.8, 115.6, 70.4, 63.7, 59.0. GC–MS: m/z [M] calcd for C₁₈H₁₆ClN₃O₃: 357.0880; found: 357.10.2-Hydroxyethyl (E)-3-(2-{[1,2,3]Triazolo[1,5-a]pyridin-3-yl}-5-chlorophenyl)but-2-enoate (4f)Yield (58.1 mg, 65% yield, semisolid), eluent 45% ethyl acetate/hexane). ¹H NMR (600 MHz, CDCl₃): δ = 8.83 (d, J = 7.1 Hz, 1 H), 7.84–7.80 (m, 2 H), 7.65 (d, J = 8.6 Hz, 2 H), 7.53 (d, J = 8.3 Hz, 1 H), 7.36–7.32 (m, 1 H), 7.10 (t, J = 6.8 Hz, 1 H), 6.60 (d, J = 15.8 Hz, 1 H), 4.33 (t, J = 4.7 Hz, 2 H), 3.65 (t, J = 4.7 Hz, 2 H), 3.41 (s, 3 H). ¹³C NMR (150 MHz, CDCl₃): δ = 168.7, 139.2, 137.2, 134.6, 131.8, 130.8, 130.2, 128.7, 128.5, 128.1, 125.6, 118.4, 115.5, 66.6, 61.4, 14.2. GC–MS: m/z [M] calcd for C₁₈H₁₆ClN₃O₃: 357.0880; found: 357.10.2,2,2-Trifluoroethyl (E)-3-(2-{[1,2,3]Triazolo[1,5-a]pyridin-3-yl}-5-chlorophenyl)acrylate (4g)Yield (84 mg, 88% yield, semisolid), eluent 25% ethyl acetate/hexane. ¹H NMR (600 MHz, CDCl₃): δ = 8.71 (d, J = 7.2 Hz, 1 H), 7.93 (d, J = 16.0 Hz, 1 H), 7.75 (d, J = 8.0 Hz, 1 H), 7.60 (d, J = 8.0 Hz, 1 H), 7.57 (d, J = 9.0 Hz, 1 H), 7.48 (t, J = 7.6 Hz, 1 H), 7.42 (q, J = 7.8, 7.3 Hz, 1 H), 6.97 (t, J = 6.9 Hz, 1 H), 6.47 (d, J = 16.0 Hz, 1 H), 4.46 (q, J = 8.1 Hz, 2 H). ¹³C NMR (150 MHz, CDCl₃): δ = 167.0, 166.6, 143.6, 143.5, 140.9, 134.7, 133.8, 130.7, 130.6, 130.4, 129.7, 129.1, 129.0, 128.3, 127.8, 123.9, 122.8, 120.3, 112.7, 52.4, 29.7. GC–MS: m/z [M] calcd for C₁₇H₁₁ClF₃N₃O₂: 381.0492; found: 381.30.(E)-3-(2-{[1,2,3]Triazolo[1,5-a]pyridin-3-yl}-5-chlorophenyl)acrylonitrile (4h).Yield (60.4 mg, 86% yield, semisolid), eluent 25% ethyl acetate/hexane. ¹H NMR (600 MHz, CDCl₃): δ = 8.24 (d, J = 7.8 Hz, 1 H), 8.02 (d, J = 6.7 Hz, 1 H), 7.80 (d, J = 8.0 Hz, 1H ), 7.72 (d, J = 9.2 Hz, 1 H), 7.48 (t, J = 7.5 Hz, 2 H), 7.39 (t, J = 7.5 Hz, 1 H), 7.20 (t, J = 7.9 Hz, 1 H), 6.81 (t, J = 6.7 Hz, 1 H). ¹³C NMR (150 MHz, CDCl₃): δ = 149.3, 145.7, 140.1, 128.9, 125.3, 125.2, 124.3, 124.1, 124.0, 122.4, 121.5, 118.2, 111.9. GC–MS: m/z [M] calcd for C₁₅H₉ClN₄: 280.0516; found: 280.0.Phenyl(pyridin-2-yl)methanone (5)¹¹ Yield (14.0 mg, 31% yield, white solid), mp 42–44 ℃), 5% ethyl acetate/hexane. ¹H NMR (600 MHz, CDCl₃): δ = 8.71 (d, J = 4.3 Hz, 1 H), 8.07 (d, J = 7.7 Hz, 2 H), 8.03 (d, J = 7.8 Hz, 1 H), 7.88 (t, J = 7.7 Hz, 1 H), 7.58 (t, J = 7.3 Hz, 1 H), 7.47 (dd, J = 14.2, 6.9 Hz, 3 H). ¹³C NMR (150 MHz, CDCl₃): δ = 193.7, 154.9, 148.4, 136.9, 136.1, 132.7, 130.8, 128.0, 126.0, 124.4.
11 Joshi A, Kumar R, Semwal R, Rawat D, Adimurthy S. Green Chem. 2019; 21: 962

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