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Rhodium-Catalyzed Synthesis of Unsymmetric Di(heteroaryl) Ethers Using Heteroaryl Exchange Reaction

Abstract

Unsymmetric di(heteroaryl) ethers were synthesized by the rhodium-catalyzed heteroaryl exchange reaction of heteroaryl aryl ethers and heteroaryl esters at equilibrium. Diverse unsymmetric di(heteroaryl) ethers containing five- and six-membered heteroarenes were obtained. Di(heteroaryl) ethers can be synthesized starting from diaryl ethers, because heteroaryl aryl ethers are obtained by the heteroaryl exchange reaction of diaryl ethers.

Key words

unsymmetric di(heteroaryl) ethers - rhodium - heteroaryl exchange reaction - C–O bond cleavage - heteroaryl benzoates

• References and Notes

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• 9 General Procedure for the Synthesis of Unsymmetric Di(heteroaryl) Ethers In a two-necked flask equipped with a magnetic stirrer bar and a reflux condenser were placed RhH(PPh₃)₄ (5 mol%, 14.4 mg), dppBz (10 mol%, 11.1 mg), 2-phenoxy-1,3-benzothiazole (2a, 0.75 mmol, 170.5 mg), and pyridine-3-yl benzoate (9, 0.25 mmol, 49.8 mg) in chlorobenzene (0.5 mL) under an argon atmosphere, and the solution was stirred and heated at reflux for 5 h. The solvent was removed under reduced pressure, and the residue was purified by flush column chromatography on silica gel giving 2-(3-pyridinyloxy)-1,3-benzothiazole (10, 69%, 39.4 mg) and phenylbenzoate (11, 70%, 34.7 mg) with recovery of 2a (73%, 124.4 mg) and 9 (25%, 12.5 mg). Analytical Data of Compound 10 Colorless solid; mp 63.0–64.0 °C (hexane). ¹H NMR (400 MHz, CDCl₃): δ = 7.31 (1 H, td, J = 1.2, 8.0 Hz), 7.41 (2 H, t, J = 8.0 Hz), 7.72 (2 H, m), 7.82 (1 H, ddd, J = 1.6, 3.2, 8.4 Hz), 8.56 (1 H, dd, J = 1.2, 4.8 Hz), 8.73 (1 H, d, J = 2.8 Hz). ¹³C NMR (100 MHz, CDCl₃): δ = 121.4, 121.9, 124.2, 124.5, 126.4, 128.0, 132.3, 142.7, 147.0, 148.7, 151.2, 170.8. IR (KBr) 3060, 1527, 1475, 1440, 1428, 1256, 1235, 1021 cm^–1. MS (EI): m/z (%) = 228 (100) [M⁺], 200 (50) [M⁺ – CN]. HRMS: m/z calcd for C₁₂H₈N₂OS: 228.0357; found: 228.0343.
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• 11 Crystallographic data including structure factors have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication number CCDC 1534272 for compound 14u. The data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/getstructures.
• 12 For a related observation see: Sawatlon B. Wititsuwannakul T. Tantirungrotechai Y. Surawatanawong P. Dalton Trans. 2014; 43: 18123