Cu(II)/TBAI-Catalyzed Esterification of Acid Hydrazides via C(sp³)–H Oxidative Coupling

Abstract

A Cu²⁺/TBAI-cocatalyzed allylic ester synthesis was developed, which allows a direct coupling of acid hydrazides and cycloalkanes. This process makes use of commercially available, inexpensive, and abundant starting materials. Based on the extensive experimental data, a plausible radical mechanism was suggested.

Key words

Cu²⁺/TBAI cocatalysis - direct coupling - acid hydrazides

• References and Notes

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• 12 Synthesis of 3a–p A mixture of 1 (0.2 mmol), cycloalkane (2 mL), Cu(OAc)₂ (10 mol%), TBAI (20 mol%), and TBHP (3 equiv) was stirred at 140 °C under N₂ atmosphere for 36 h. The reaction mixture was washed with H₂O and the aqueous phase was extracted with EtOAc (3×). The combined organic layer was washed with brine, dried over Na₂SO₄, and evaporated under reduced pressure. The crude product was purified by silica gel column chromatography to give the corresponding product. Compound 3a: yield 61%. ¹H NMR (500 MHz, CDCl₃): δ = 8.06 (d, J = 8.4 Hz, 2 H), 7.55 (m, 1 H), 7.42 (dd, J = 8.2, 7.0 Hz, 2 H), 6.01 (m, 1 H), 5.85 (m, 1 H), 5.51 (m, 1 H), 2.15 (m, 1 H), 2.04 (m, 1 H), 1.96 (m, 1 H), 1.84 (m, 1 H), 1.68 (m, 1 H). ¹³C NMR (125 MHz, CDCl₃): δ = 166.2, 132.8, 132.7, 130.8, 129.5, 128.2, 125.7, 68.5, 28.4, 24.9, 18.9. HRMS: m/z calcd for C₁₃H₁₄O₂ [M]⁺: 202.2491; found: 202.2488. Compound 3b: yield 70%. ¹H NMR (500 MHz, CDCl₃): δ = 8.00 (d, J = 9.0 Hz, 2 H), 6.90 (d, J = 9.0 Hz, 2 H), 5.96 (m, 1 H), 5.81 (m, 1 H), 5.45 (m, 1 H), 3.82 (s, 3 H), 2.04 (m, 3 H), 1.82 (m, 2 H), 1.67 (m, 1 H). ¹³C NMR (125 MHz, CDCl₃): δ = 165.9, 163.2, 132.5, 131.5, 125.9, 123.2, 113.4, 68.2, 55.3, 28.4, 24.9, 18.9. HRMS: m/z calcd for C₁₄H₁₆O₃ [M]⁺: 232.2750; found: 232.2755. Compound 3c: yield 58%. ¹H NMR (500 MHz, CDCl₃): δ = 7.70 (m, 2 H), 7.13 (m, 2 H), 5.80 (m, 1 H), 5.68 (m, 1 H), 5.35 (m, 1 H), 2.20 (m, 3 H), 1.99–1.65 (m, 6 H). ¹³C NMR (125 MHz, CDCl₃): δ = 165.8, 137.5, 133.1, 132.2, 130.3, 129.6, 127.7, 126.4, 125.2, 68.0, 28.1, 24.6, 20.8, 18.6.. HRMS: m/z calcd for C₁₄H₁₆O₃ [M]⁺: 232.2750; found: 232.2753 Compound 3d: yield 72%. ¹H NMR (500 MHz, CDCl₃): δ = 7.52 (dd, J = 8.4, 2.0 Hz, 1 H), 7.40 (d, J = 2.0 Hz, 1 H), 6.69 (m, 1 H), 5.83 (m, 1 H), 5.68 (m, 1 H), 5.28 (m, 1 H), 3.75 (s, 3 H), 3.70 (s, 3 H), 2.20–1.40 (m, 6 H). ¹³C NMR (125 MHz, CDCl₃): δ = 165.4, 152.4, 148.1, 132.0, 125.5, 123.0, 122.8, 111.5, 109.7, 67.9, 55.4, 28.1, 24.5, 18.2. HRMS: m/z calcd for C₁₅H₁₈O₄ [M]⁺: 262.3010; found: 262.3013. Compound 3e: yield 39%. ¹H NMR (500 MHz, CDCl₃): δ = 7.90 (d, J = 8.6 Hz, 2 H), 7.56 (d, J = 8.6 Hz, 2 H), 6.01 (m, 1 H), 5.832 (m, 1 H), 5.50 (m, 1 H), 2.05 (m, 3 H), 1.83 (m, 2 H), 1.70 (m, 1 H). ¹³C NMR (125 MHz, CDCl₃): δ = 165.3, 132.8, 131.4, 130.99, 129.7, 127.67, 125.9, 68.8, 28.4, 24.8, 18.2.. HRMS: m/z calcd for C₁₃H₁₃BrO₂ [M]⁺: 281.1451; found: 281.1450. Compound 3f: yield 30%. ¹H NMR (500 MHz, CDCl₃): δ = 8.28 (d, J = 8.8 Hz, 2 H), 8.22 (d, J = 8.8 Hz, 2 H), 6.05 (m, 1 H), 5.84 (m, 1 H), 5.55 (m, 1 H), 2.19–1.72 (m, 6 H). ¹³C NMR (125 MHz, CDCl₃): δ = 164.0, 150.1, 135.9, 133.9, 130.4, 124.7, 123.2, 69.6, 28.0, 24.7, 18.6. HRMS: m/z calcd for C₁₃H₁₃NO₄ [M]⁺: 247.2466; found: 247.2463. Compound 3g: yield 33%. ¹H NMR (500 MHz, CDCl₃): δ = 8.07 (m, 2 H), 7.10 (m, 2 H), 6.01 (m, 1 H), 5.82 (m, 1 H), 5.50 (m, 1 H), 2.06 (m, 3 H), 1.85 (m, 2 H), 1.70 (m, 1 H). ¹³C NMR (125 MHz, CDCl₃): δ = 166.9, 165.2, 164.3, 132.9, 132.1, 132.0, 126.9, 125.5, 115.4, 115.2, 68.7, 28.3, 24.9, 18.9. HRMS: m/z calcd for C₁₃H₁₃FO₂ [M]⁺: 220.2395; found: 220.2393. Compound 3h: yield 45%. ¹H NMR (500 MHz, CDCl3): δ = 7.98 (d, J = 8.4 Hz, 2 H), 7.40 (d, J = 8.4 Hz, 2 H), 6.01 (m, 1 H), 5.82 (m, 1 H), 5.50 (m, 1 H), 2.05 (m, 3 H), 1.83 (m, 2 H), 1.70 (m, 1 H). ¹³C NMR (125 MHz, CDCl₃): δ = 165.2, 139.0, 132.9, 130.9, 129.1, 128.5, 125.4, 68.8, 28.3, 24.8, 18.8. HRMS: m/z calcd for C₁₃H₁₃ClO₂ [M]⁺: 236.6941; found: 236.6945. Compound 3i: yield 37%. ¹H NMR (500 MHz, CDCl3): δ = 7.80 (m, 1 H), 7.53 (m, 1 H), 7.08 (m, 1 H), 6.00 (m, 1 H), 5.81 (m, 1 H), 5.47 (m, 1 H), 2.03 (m, 3 H), 1.84 (m, 2 H), 1.68 (m, 1 H). ¹³C NMR (125 MHz, CDCl₃): δ = 161.8, 134.3, 133.1, 132.9, 132.0, 127.5, 125.4, 68.8, 28.2, 24.8, 18.8. HRMS: m/z calcd for C₁₁H₁₂SO₂ [M]⁺: 208.2768; found: 208.2770. Compound 3j: yield 21%. ¹H NMR (500 MHz, CDCl₃): δ = 7.92 (m, 1 H), 7.64 (m, 1 H), 7.15 (m, 1 H), 6.21 (m, 1 H), 5.89 (m, 1 H), 5.67 (m, 1 H), 2.3 (m, 3 H), 1.88 (m, 2 H), 1.78 (m, 1 H). ¹³C NMR (125 MHz, CDCl₃): δ = 162.5, 134.9, 134.1, 132.9, 132.0, 128.3, 125.9, 68.8, 28.5, 24.3, 18.1. HRMS: m/z calcd for C₁₁H₁₂O₃ [M]⁺: 192.2112; found: 192.2110. Compound 3m: yield 65%. ¹H NMR (500 MHz, CDCl₃): δ = 8.02 (d, J = 8.4 Hz, 2 H), 7.53 (t, J = 7.2 Hz, 1 H), 7.40 (m, 2 H), 6.18 (m, 1 H), 5.92 (m, 2 H), 2.65 (m, 1 H), 2.33 (m, 2 H), 1.90 (m, 1 H). ¹³C NMR (125 MHz, CDCl₃): δ = 166.6, 137.7, 132.7, 130.7, 129.5, 129.4, 128.2, 81.1, 31.2, 29.9. HRMS: m/z calcd for C₁₂H₁₂O₂ [M]⁺: 288.2225; found: 188.2220. Compound 3n: yield 43%. ¹H NMR (500 MHz, CDCl₃): δ = 8.08 (m, 2 H), 7.57 (m, 1 H), 7.42 (m, 2 H), 5.91 (m, 1 H), 5.79 (m, 1 H), 5.66 (m, 1 H), 2.27 (m, 1 H), 2.14 (m, 1 H), 2.01 (m, 2 H), 1.90–1.66 (m, 3 H), 1.53–1.45 (m, 1 H). ¹³C NMR (125 MHz, CDCl₃): δ = 166.1, 133.7, 133.0, 132.2, 130.9, 129.8, 128.5, 74.9, 33.1, 28.8, 26.9, 26.8. HRMS: m/z calcd for C₁₄H₁₆O₂ [M]⁺: 216.2756; found: 216.2751. Compound 3o: yield 68%. ¹H NMR (500 MHz, CDCl₃): δ = 8.02 (d, J = 8.4 Hz, 2 H), 7.55 (t, J = 8.4 Hz, 1 H), 7.43 (t, J = 7.6 Hz, 2 H), 5.93 (m, 1 H), 5.72 (m, 1 H), 5.61 (m, 1 H), 2.33 (m, 1 H), 2.15 (m, 1 H), 2.04 (m, 1 H), 1.66 (m, 6 H), 1.42 (m, 1 H). ¹³C NMR (125 MHz, CDCl₃): δ = 166.0, 132.7, 130.7, 130.7, 129.8, 129.5, 128.2, 73.0, 35.1, 28.8, 26.4, 25.9, 23.4. HRMS: m/z calcd for C₁₅H₁₈O₂ [M]⁺: 230.3022; found: 230.3019.