Palladium Assisted Substitution of 3-Benzo[b]furan Triflates

Abstract

Triflates of 3-coumaranones were prepared, and experimented as coupling partners in palladium catalyzed Stille, Heck, Suzuki, and Sonogashira coupling reactions. The corresponding 3-substituted benzo[b]furans were obtained in excellent yields.

Key words

3-coumaranone - triflate - benzofuran - palladium - catalysis

References

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10

Coumaranone 2a was purchased from Avocado.

12

Preparation of Benzo[b]furan 3-yl Trifluoromethane Sulfonate(2a)
N,N-diisopropylethylamine (1.1 g, 8.51 mmol, Hünig’s base) was added dropwise to a stirred solution of 2a (1 g, 7.46 mmol) in dry CH₂Cl₂ under nitrogen at -10 °C. Trifluoromethanesulfonic anhydride (2.5 g, 8.86 mmol) was then added and the mixture was allowed to stand at r.t. for 16 h. The mixture was hydrolyzed with water (5 mL). The organic layer was washed with water, dried over anhydrous Na₂SO₄ and evaporated in vacuo. The residue was purified by chromatography on silica gel eluenting with hexane-Et₂O: 80/20 to give 2a as a yellow oil (1.60 g, 81%). ¹H NMR (300 MHz, CDCl₃, 25 °C): δ = 7.38 (td, J = 7.2 and 1.3 Hz, 1 H), 7.44 (td, J = 7.2 and 1.3 Hz, 1 H), 7.54 (dd, J = 7.2 and 1.3 Hz, 1 H), 7.65 (dd, J = 7.2 and 1.3 Hz, 1 H), 7.84 (s, 1 H); ¹³C (50 MHz, CDCl₃, 25 °C): δ = 111.2, 118.1, 118.8 (q, J = 320 Hz), 120.2, 124.1, 126.2, 134.1, 135.3, 153.2.

16

Selected Physical Data: 4b(oil);¹H NMR (300 MHz, CDCl₃, 25 °C): δ =3.95 (s, 3 H), 7.38 (d, J = 8.7 Hz, 1 H), 7.45 (dd, J = 8.7 and 2.2 Hz, 1 H), 8.19 (d, J = 2.2 Hz, 1 H), 8.24 (s, 1 H); ¹³C NMR (75 MHz, CDCl₃, 25 °C): δ = 51.8, 113.1, 114.1, 117.6, 124.8, 126.4, 151.8, 154.3, 163.1, 178.6. HMRS: m/z calcd for C₁₀H₇BrO₃: 253.9578; found: 253.9570. 6b(oil); ¹H NMR (300 MHz, CDCl₃, 25 °C): δ = 5.36-5.40 (dd, J = 11.2 and 1.2 Hz, 1 H), 5.66-5.74 (dd, J = 17.5 and 1.2 Hz, 1 H), 6.84-6.90 (dd, J = 17.5 and 11.2 Hz, 1 H), 7.37-7.40 (d, J = 8.7 Hz, 1 H), 7.44-7.47 (dd, J = 8.7 and 2.2 Hz, 1 H), 8.19 (d, J = 2.2 Hz, 1 H), 8.24 (s, 1 H). HMRS:
m/z calcd for C₁₀H₇BrO: 221.9680; found: 221.9676. 7b(oil); ¹H NMR (300 MHz, CDCl₃, 25 °C): δ = 2.14 (brs, 1 H), 4.58 (s, 2 H), 7.35 (d, J = 8.7 Hz, 1 H), 7.43 (dd, J = 8.7 and 1.9 Hz), 7.78 (s, 1 H), 7.80 (d, J = 1.9 Hz, 1 H); ¹³C NMR (75 MHz, CDCl₃, 25 °C): δ = 51.6, 74.5, 92.5, 103.5, 113.1, 116.6, 123.1, 128.2, 129.3, 148.8, 153.2. HMRS: m/z calcd for C₁₁H₇BrO₂: 249.9629; found: 249.9621. 9a(oil); ¹H NMR (300 MHz, CDCl₃, 25 °C): δ = 1.62 (brs, 2 H), 3.71 (s, 2 H), 7.23-7.46 (m, 2 H), 7.47-7.55 (m, 1 H), 7.60-7.72 (m, 1 H), 7.77 (s, 1 H); ¹³C NMR (75 MHz, CDCl₃, 25 °C): δ = 32.0, 71.5, 94.6, 104.0, 111.2, 120.0, 122.9, 124.8, 127.3, 147.1, 154.2. 10c (mp 92 °C); ¹H NMR (300 MHz, CDCl₃, 25 °C): δ = 4.02 (s, 3 H), 5.98 (d, J = 16.5 Hz, 1 H), 6.90-6.93 (dd, J = 6.2 and 2.5 Hz, 1 H), 7.23-7.29 (m, 2 H), 7.42-7.48 (d, J = 16.5 Hz, 1 H), 7.86 (s, 1 H). C₁₂H₉NO₂ (199.02): calcd C, 72.35; H, 4.55; N, 7.03. Found: C, 72.40; H, 4.61; N, 6.91. 11c(oil); ¹H NMR (300 MHz, CDCl₃, 25 °C): δ = 4.08 (s, 3 H), 6.89-6.94 (dd, J = 7.8 and 1.2 Hz, 1 H), 7.24-7.32 (t, J = 7.8 Hz, 1 H), 7.40-7.44 (dd, J = 7.8 and 1.2 Hz, 1 H), 7.46-7.50 (d, J = 8.8 Hz, 2 H), 7.58-7.62 (d, J = 8.8 Hz, 2 H), 7.84 (s, 1 H). HMRS: m/z calcd for C₁₅H₁₁ClO: 258.0447; found: 258.0451.