Regioselective Anodic Fluorination of α-(Arylthio)benzylphosphonate Esters, α-(Arylthio)methylphosphonate Esters and Their Analogues

Asami Hidaka; Bakenova Zagipa; Hirokatsu Nagura; Toshio Fuchigami

doi:10.1055/s-2007-977439

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Synlett 2007(7): 1148-1152
DOI: 10.1055/s-2007-977439

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Regioselective Anodic Fluorination of α-(Arylthio)benzylphosphonate Esters, α-(Arylthio)methylphosphonate Esters and Their Analogues

Asami Hidaka, Bakenova Zagipa, Hirokatsu Nagura, Toshio Fuchigami*
Department of Electronic Chemistry, Tokyo Institute of Technology, Nagatsuta, Midori-ku, Yokohama 226-8502, Japan
Fax: +81(45)9245406; e-Mail: fuchi@echem.titech.ac.jp;

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Publication History

Received 5 January 2007
Publication Date:
13 April 2007 (online)

Abstract
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Abstract

Regioselective anodic α-fluorination of α-(arylthio)benzylphosphonate esters and [(arylthio)methyl]- and [(heteroarylthio)methyl]phosphonate esters was successfully carried out at a glassy carbon anode or platinum anode in dimethoxyethane and nitromethane to provide the corresponding α-fluorophosphonate esters in excellent to moderate yields.

Key words

electrochemical fluorination - α-fluorophosphonate ester - Emmons-Wittig reagent - anodic substitution - electrosynthesis

References and Notes

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12

Typical procedure for anodic fluorination: Anodic oxidation of 1 (0.5 mmol) was carried out in an undivided cell equipped with a GC plate anode (2 × 2 cm²) and platinum plate cathode (2 × 2 cm²) in Et₄NF·3HF-DME (1 M, 5 mL) at r.t. Constant current (2.5 mA/cm²) was passed until the starting material 1 was almost consumed (monitored by TLC). After electrolysis, the electrolytic solution was passed through a short column filled with silica gel using EtOAc as an eluent to remove fluoride salts. The eluent was evaporated under reduced pressure, and the residue was further purified by column chromatography on silica gel using EtOAc to give pure fluorinated products. The products were identified by spectroscopic data.

13

Diethyl α-Fluoro-α-(phenylthio)benzylphosphonate (2a): ¹H NMR (CDCl₃): δ = 1.11 (t, J = 7.09 Hz, 3 H), 1.31 (t, J = 7.09 Hz, 3 H), 3.69-3.79 (m, 1 H), 3.91-4.02 (m, 1 H), 4.05-4.22 (m, 2 H), 7.13-7.55 (m, 10 H); ¹³C NMR (CDCl₃): δ = 16.3 (d, J _PC = 11.7 Hz), 16.4 (d, J _PC = 11.7 Hz), 64.4 (dd, J _FC = 0.02 Hz, J _PC = 7.27 Hz), 64.6 (dd, J _FC = 0.02 Hz, J _PC = 7.27 Hz), 106.2 (dd, J _PC = 175.7 Hz, J _FC = 234.3 Hz), 126.3 (t, J = 3.91 Hz), 126.4 (t, J = 3.91 Hz), 127.7 (t, J _PC = J _FC = 1.68 Hz), 128.3, 128.7 (d, J = 1.68 Hz), 129.0, 134.8 (d, J = 22.4 Hz), 135.9 (d, J = 2.24 Hz);¹⁹F NMR (CDCl₃): δ = -67.3 (d, J _PF = 90.4 Hz); HRMS: m/z calcd for C₁₇H₂₀FO₃PS: 354.0855; found: 354.0843.

14

Diethyl α-Fluoro-α-(phenylthio)-4-methoxybenzylphos-phonate (6): ¹H NMR (CDCl₃): δ = 1.14 (t, J = 6.75 Hz, 3 H), 1.32 (t, J = 6.75 Hz, 3 H), 3.80 (s, 3 H), 3.91-3.97 (m, 1 H), 4.07-4.19 (m, 1 H), 4.29-4.33 (m, 2 H), 6.83 (d, J = 8.64 Hz, 2 H), 7.36-7.58 (m, 5 H), 7.63 (d, J = 7.83 Hz, 2 H); ¹³C NMR (CDCl₃): δ = 16.1 (d, J _PC = 5.56 Hz), 16.3 (d, J _PC = 5.56 Hz), 64.6 (dd, J _FC = 1.68 Hz, J _PC = 7.25 Hz), 65.2 (d, J _PC = 6.70 Hz), 106.4 (dd, J _PC = 162.3 Hz, J _FC = 229.2 Hz), 113.4 (t, J _PC = J _FC = 1.68 Hz), 113.6 (t, J _PC = J _FC = 1.68 Hz), 127.7 (d, J _PC = 3.35 Hz), 127.8 (d, J _PC = 3.35 Hz), 130.4, 134.1, 134.5 (d, J = 2.80 Hz), 160.6;¹⁹F NMR (CDCl₃): δ = -89.0 (d, J _PF = 68.3 Hz); HRMS: m/z calcd for C₁₈H₂₂FO₆PS: 416.0859; found: 416.0862.

15

Diethyl α-Fluoro-α-(phenylthio)-4-iodebenzylphos-phonate (7): ¹H NMR (CDCl₃): δ = 1.09 (t, J = 7.09 Hz, 3 H), 1.29 (t, J = 7.09 Hz, 3 H), 3.69-3.78 (m, 1 H), 3.93-4.01 (m, 1 H), 4.09-4.22 (m, 2 H), 7.13-7.25 (m, 5 H), 7.40 (d, J = 7.03 Hz, 2 H), 7.54 (d, J = 7.03 Hz, 2 H); ¹³C NMR (CDCl₃): δ = 16.2 (d, J _FC = 11.7 Hz), 16.4 (d, J _PC = 11.7 Hz), 64.3 (dd, J _FC = 1.68 Hz, J _PC = 7.27 Hz), 64.6 (dd, J _FC = 1.68 Hz, J _PC = 7.27 Hz), 106.0 (dd, J _PC = 174.6 Hz, J _FC = 233.7 Hz), 126.3 (t, J _PC = J _FC = 7.83 Hz), 126.4 (t, J _PC = J _FC = 7.83 Hz), 127.7 (t, J _PC = J _FC = 1.68 Hz), 128.3, 128.6 (d, J = 7.83 Hz), 129.0, 134.9 (d, J = 22.9 Hz), 135.8 (d, J = 1.68 Hz);¹⁹F NMR (CDCl₃): δ = -67.3 (d, J _PF = 64.5 Hz); HRMS: m/z calcd for C₁₇H₁₉FIO₃PS: 479.9821; found: 479.9809.

16

Diethyl [Fluoro(2-naphthyl)(phenylthio)methyl]phos-phonate (8): ¹H NMR (CDCl₃): δ = 1.07 (t, J = 7.02 Hz, 3 H), 1.28 (t, J = 7.02 Hz, 3 H), 3.65-3.78 (m, 1 H), 3.91-4.04 (m, 1 H), 4.12-4.25 (m, 2 H), 7.07-7.16 (m, 3 H), 7.41-7.47 (m, 4 H), 7.47-7.79 (m, 4 H), 7.94 (m, 1 H); ¹³C NMR (CDCl₃): δ = 16.3 (d, J _PC = 5.56 Hz), 16.4 (d, J _PC = 5.56 Hz), 64.5 (d, J _PC = 7.26 Hz), 65.2 (d, J _PC = 7.26 Hz), 106.2 (dd, J _PC = 176.8 Hz, J _FC = 234.3 Hz), 124.0 (dd, J _PC = 2.80 Hz, J _FC = 5.59 Hz), 125.8 (dd, J _PC = 5.59 Hz, J _FC = 9.50 Hz), 126.1, 126.5, 127.4, (d, J _FC = 6.10 Hz), 128.4, 128.5, 128.8, 132.4 (t, J _FC = 11.1 Hz), 132.8, 135.8;¹⁹F NMR (CDCl₃): δ = -65.9 (d, J _PF = 92.5 Hz); HRMS: m/z calcd for C₂₁H₂₂FO₃PS: 404.1011; found: 404.1007.

17

Diethyl α-Fluoro-α-(2-pyridylthio)benzylphosphonate (11): ¹H NMR (CDCl₃): δ = 1.14 (t, J = 7.02 Hz, 3 H), 1.26 (t, J = 7.02 Hz, 3 H), 3.89 (q, J = 7.29 Hz, 1 H), 4.14 (q, J = 6.48 Hz, 1 H), 4.34 (q, J = 6.9 Hz, 2 H), 6.90-7.56 (m, 8 H), 8.34 (d, J = 4.86 Hz, 1 H); ¹³C NMR (CDCl₃): δ = 16.33 (d, J _PC = 10.62 Hz), 16.39 (d, J _PC = 10.65 Hz), 64.7 (dd, J _PC = 7.29 Hz, J _FC = 31.02 Hz), 65.1 (dd, J _PC = 6.78 Hz, J _FC = 22.87 Hz), 106.21 (dd, J _PC = 170.11 Hz, J _FC = 230.11 Hz), 126,3 (t, J _PC = 3.91 Hz), 126.6 (t, J _PC = 3.91 Hz), 127.9 (s), 128.2 (t, J = 1.69 Hz), 129.1 (t, J = 1.68 Hz), 134.5 (d, J = 22.42 Hz), 149.19 (s);¹⁹F NMR (CDCl₃): δ = -66.28 (d, J _PF = 92.2 Hz); HRMS: m/z calcd for C₁₆H₁₉FNO₃PS: 355.0807; found: 355.0800.

18

Diethyl α-Fluoro-α-(4-pyridylthio)benzylphosphonate (12): ¹H NMR (CDCl₃): δ = 1.13 (t, J = 7.02 Hz, 3 H), 1.29 (t, J = 7.02 Hz, 3 H), 3.86 (q, J = 7.29 Hz, 1 H), 4.01 (q, J = 7.02 Hz, 1 H), 4.15 (q, J = 6.95 Hz, 2 H), 7.16-7.53 (m, 5 H), 7.57 (d, J = 6.92 Hz, 2 H), 8.34 (d, J = 5.21 Hz, 2 H); ¹³C NMR (CDCl₃): δ = 16.30 (d, J _PC = 10.62 Hz), 16.38 (d, J _PC = 10.62 Hz), 64.76 (dd, J _PC = 7.25 Hz, J _FC = 22.85 Hz), 65.1 (dd, J _PC = 6.71 Hz, J _FC = 22.31 Hz), 106.1 (dd, J _PC = 169.52 Hz, J _FC = 229.8 Hz), 126,3 (t, J _PC = 3.91 Hz), 126.6 (t, J _PC = 3.91 Hz), 127.6 (s), 128.1 (t, J = 1.68 Hz), 128.9 (t, J = 1.68 Hz), 134.1 (d, J = 22.36 Hz), 149.17 (s); ¹⁹F NMR (CDCl₃): δ = -66.67 (d, J _PF = 86.9 Hz); HRMS: m/z calcd for C₁₆H₁₉FNO₃PS: 355.0807; found: 355.0789.

22

Diethyl [Fluoro(4-pyridylthio)methyl]phosphonate (19): ¹H NMR (CDCl₃): δ = 1.37 (t, J = 7.09 Hz, 6 H), 4.24-4.36 (m, 4 H), 6.19 (dd, J _HF = 53.6 Hz, J _HP = 7.56 Hz, 1 H, CHF), 7.34 (d, J = 1.48 Hz, 1 H), 7.36 (d, J = 1.48 Hz, 1 H), 8.53 (d, J = 1.48 Hz, 1 H), 8.55 (d, J = 1.48 Hz, 1 H); ¹³C NMR (CDCl₃): δ = 16.65 (d, J _PC = 6.15 Hz), 64.5 (dd, J _PC = 6.70 Hz, J _FC = 11.7 Hz), 93.7 (dd, J _PC = 177.2 Hz, J _FC = 232.5 Hz, CHF), 122.9 (d, J _FC = 1.68 Hz), 144.5 (d, J _PC = 2.80 Hz), 144.7 (d, J _PC = 2.80 Hz), 149.9 (s); ¹⁹F NMR (CDCl₃): δ = -93.6 (dd, J _PF = 83.3 Hz, J _HF = 53.6 Hz); HRMS: m/z calcd for C₁₀H₁₅FNO₃PS: 279.0494; found: 279.0489.