Silver-Catalyzed 2-Pyridyl Arylation of Pyridine N-Oxides with Arylboronic Acids at Room Temperature

Abstract

A novel direct arylation of pyridine N-oxides with arylboronic acids through C-H functionalization has been developed. This new reaction is performed at room temperature using catalytic silver(I) nitrate in the presence of potassium persulfate and give 2-pyridyl arylation derivatives of pyridine N-oxides.

Key words

silver - pyridine N-oxides - arylation

References and Notes

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13

General Procedure for this Reaction A 50 mL vial was charged with a magnetic stir bar, pyridine N-oxide (1a, 1.5 mmol), phenylboronic acid (2a, 1.0 mmol), AgNO₃ (0.2 mmol), K₂S₂O₈ (3.0 mmol), followed by CH₂Cl₂ and deionized H₂O (1:1, v/v, 30 mL in total). After stirring at r.t. for 18 h, the reaction mixture was filtered through Celite (washed with MeOH and CH₂Cl₂), extracted with CH₂Cl₂ (3 × 10 mL). The combined organic phase was dried over Na₂SO₄, then evaporated under reduced pressure, and the isolated yield was obtained by flash chromatography column on silica gel (gradient eluent of MeOH in CH₂Cl₂:
1-5%, v/v).

14

The metal sources used here [AgNO₃, Cu(OAc)₂, CuCl₂, FeCl₃] were all purchased from Aladdin Company in Shanghai. AR grade of AgNO₃ (>99.8%), AR grade of Cu(OAc)₂ (anhyd, >99.0%), AR grade of CuCl₂ (anhyd, >98.0%), AR grade of FeCl₃ (anhyd, >97.5%).
2-Phenylpyridine N -Oxide (3aa) ^{6 ¹}H NMR (400 MHz, CDCl₃, 293 K): δ = 7.26-7.33 (m, 1 H), 7.41-7.45 (m, 1 H), 7.47-7.53 (m, 4 H), 7.80-7.83 (m, 2 H), 8.48 (d, J = 6.4 Hz, 1 H). ^¹³C NMR (100 MHz, CDCl₃, 293 K): δ = 149.4, 140.6, 132.6, 129.7, 129.3, 128.3, 127.5, 126.0, 124.6. Mp 144-146 ˚C (CH₂Cl₂).
2-(2-Methoxyphenyl)-6-methylpyridine N -Oxide (3bb) ^¹H NMR (400 MHz, CDCl₃, 293 K): δ = 7.40-7.45 (t, J = 8.4 Hz, 1 H), 7.35-7.37 (d, J = 7.6 Hz, 1 H), 7.16-7.25 (m, 3 H), 6.99-7.06 (m, 2 H), 3.80 (s, 3 H), 2.57 (s, 3 H). ^¹³C NMR (100 MHz, CDCl₃, 293 K): δ = 157.3, 149.5, 147.9, 130.7, 125.9, 125.2, 124.1, 122.9, 120.5, 111.2, 55.8, 18.4. ESI-MS: m/z = 216.0 [M + 1]⁺. ESI-HRMS: m/z [M + H]⁺ calcd for C₁₃H₁₄NO₂ ⁺: 216.1025; found: 216.1021.
2-(2-Methylphenyl)pyridine N -Oxide (3bc) ^{6 ¹}H NMR (400 MHz, CDCl₃, 293 K): δ = 8.37 (d, J = 4.8 Hz, 1 H), 7.36-7.40 (m, 1 H), 7.24-7.32 (m, 6 H), 2.25 (s, 3 H). ^¹³C NMR (100 MHz, CDCl₃, 293 K): δ = 150.8, 140.1, 137.8, 132.9, 130.1, 129.6, 129.3, 128.0, 125.9, 125.4, 125.0, 19.5. Mp 107-109 ˚C (CH₂Cl₂).
2-(4-Methoxyphenyl)pyridine N -Oxide (3ad) ^{6 ¹}H NMR (400 MHz, CDCl₃, 293 K): δ = 8.35 (d, J = 6.4 Hz, 1 H), 7.80 (d, J = 8.8 Hz, 2 H), 7.43 (d, J = 7.6 Hz, 1 H), 7.32 (t, J = 7.6 Hz, 1 H), 7.21 (t, J = 6.4 Hz, 1 H), 7.02 (d, J = 8.8 Hz, 2 H), 3.87 (s, 3 H). ^¹³C NMR (100 MHz, CDCl₃, 293 K): δ = 160.7, 149.2, 140.6, 130.9, 127.1, 126.7, 124.6, 123.9, 113.8, 55.4. Mp 120-122 ˚C (CH₂Cl₂).
2-(3-Acetylphenyl)pyridine N -Oxide (3ae) ^¹H NMR (400 MHz, CDCl₃, 293 K): δ = 8.35-8.39 (m, 2 H), 8.07 (t, J = 8.0 Hz, 2 H), 7.60 (t, J = 8.0 Hz, 1 H), 7.50 (t, J = 6.0 Hz, 1 H), 7.36 (t, J = 7.2 Hz, 1 H), 7.26-7.31 (m, 1 H), 2.65 (s, 3 H). ^¹³C NMR (100 MHz, CDCl₃, 293 K): δ = 197.6, 148.3, 140.5, 137.1, 133.9, 133.0, 129.3, 128.6, 127.4, 126.2, 125.2, 26.7. ESI-MS: m/z [M + 1]⁺ = 214.1. ESI-HRMS: m/z [M + H]⁺ calcd for C₁₃H₁₂NO₂ ⁺: 214.0868; found: 214.0866.