An Efficient Copper-Catalyzed One-Pot Synthesis of Diaryl Thioethers by Coupling of Arylboronic Acids with Potassium Ethyl Xanthogenate under Mild Conditions

Abstract

A simple and environmentally benign one-pot synthesis of diaryl thioethers by coupling of arylboronic acids with potassium ethyl xanthogenate through a double arylation process has been developed. The aryl thiols were generated in situ, and the reactions proceeded smoothly to give the corresponding products in good to excellent yields under very mild conditions.

Key words

diaryl thioethers - arylboronic acids - potassium ethyl xanthogenate - one-pot synthesis - copper-catalyzed

References and Notes

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13

Typical Procedure for the Synthesis of Diaryl and Aryl Alkyl Thioethers
A mixture of arylboronic acid (0.75 mmol), CuCl (3.7 mg, 0.0375 mmol), potassium ethyl xanthogenate (120.2 mg, 0.75 mmol), and MeOH (3.0 mL) were taken in a flask at r.t. under N₂. The reaction mixture was stirred for a certain time under reflux conditions. After disappearance of arylboronic acid (monitored by TLC), the reaction mixture was allowed to cool down to r.t., KOH (168.3 mg, 3 mmol) and another arylboronic acid or alkyl halide (0.50 mmol for unsym-metrical thioethers, 0.75 mmol for symmetrical diaryl thioethers) were added, and the resulting mixture was further heated for a certain time (monitored by TLC). After reaction, the mixture was extracted with EtOAc and H₂O. The organic layer was dried over anhyd Na₂SO₄, and the solvent was removed under reduced pressure. The crude residue was purified by column chromatography on silica gel using EtOAc-hexanes as eluents to give the corresponding thioethers. All the thioethers are known compounds and identified by comparison of their physical and spectral data with those of authentic samples.
Bis(4-Methoxyphenyl)sulfane (3c)
Colorless oil. ^¹H NMR (400 MHz, CDCl₃): δ = 3.79 (s, 6 H), 6.81-6.86 (m, 4 H), 7.25-7.30 (m, 4 H). ^¹³C NMR (100 MHz, CDCl₃): δ = 55.5, 114.9, 127.6, 132.9, 159.1. HRMS: m/z [M + H]⁺ calcd for C₁₄H₁₅O₂S: 247.0793; found: 247.0783.
(3-Methoxyphenyl)(phenyl)sulfane (5g)
Colorless oil. ^¹H NMR (400 MHz, CDCl₃): δ = 3.73 (s, 3 H), 6.73-6.78 (m, 1 H), 6.83-6.85 (m, 1 H), 6.86-6.90 (m, 1 H), 7.17 (d, J = 8.4 Hz, 1 H), 7.20-7.31 (m, 3 H), 7.33-7.37 (m, 2 H). ^¹³C NMR (100 MHz, CDCl₃): δ = 55.4, 112.9, 116.0, 123.1, 127.4, 129.4, 130.1, 131.6, 135.4, 137.4, 160.2. HRMS: m/z [M + H]⁺ calcd for C₁₃H₁₃OS: 217.0687; found: 217.0688.
Benzyl Phenyl Sulfide (Table 4, Entry 1)
White solid; mp 40-42 ˚C. ^¹H NMR (400 MHz, CDCl₃): δ = 4.11 (s, 2 H), 7.14-7.34 (m, 10 H). ^¹³C NMR (100 MHz, CDCl₃): δ = 39.2, 126.5, 127.3, 128.6, 128.9, 129.0, 130.0, 136.5, 137.6. HRMS: m/z [M + K]⁺ calcd for C₁₃H₁₂SK: 239.0297; found: 239.0289.