DDQ-Promoted C–S Bond Formation: Synthesis of 2-Aminobenzothiazole Derivatives under Transition-Metal-, Ligand-, and Base-Free Conditions

Abstract

A transition-metal-free method for the intramolecular S-arylation of o-halobenzothiaoureas via DDQ-mediated leading to the 2-aminobenzothiazole derivatives is reported. The reactions are performed at room temperature under ligand- and base-free conditions with good to excellent yields.

Key words

2-aminobenzothiazoles - transition-metal-free - ligand-free - DDQ - S-arylation

• References and Notes

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For metal-catalyzed intramolecular cyclizations of 2-halobenzothioureas, see:
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Tandem addition–C–S coupling reaction:
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See also:
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See also:
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See further:
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See also:
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• 11 Typical Procedure To a solution of (o-iodoaryl) thiaoureas (1.0 mmol) in DMSO (3 mL) were added DDQ in five equal portions. The mixture was stirred at r.t. for 24 h (TLC monitoring). After the reaction was completed, H₂O (10 mL) and a sat. aq NaHCO₃ solution (5 mL) were added, and then the aqueous solution was extracted with EtOAc (3 × 15 mL). The combined organic extracts were dried over anhyd Na₂SO₄ and concentrated, and then the residue was purified by column chromatography [eluent: PE–EtOAc (5:1 to 7:1)] on silica gel to provide the desired product. Compound 2a: ¹H NMR (400 MHz, CDCl₃): δ = 7.16–7.18 (m, 2 H), 7.33 (t, J = 7.3 Hz, 1 H), 7.40 (t, J = 8.3 Hz, 2 H), 7.50 (d, J = 7.7 Hz, 2 H), 7.60 (d, J = 8.0 Hz, 1 H), 7.63 (d, J = 7.9 Hz, 1 H) ppm. ¹³C NMR (100 MHz, CDCl₃): δ = 119.5, 120.0, 120.8, 122.6, 124.3, 126.2, 129.6, 130.0, 139.7, 151.4, 164.1 ppm. ESI-HRMS: m/z calcd for [C₁₃H₁₀N₂S + H]⁺ : 227.0643; found: 227.0649. Compound 2c: ¹H NMR (400 MHz, DMSO-d ₆): δ = 7.14 (t, J = 8.4 Hz, 1 H), 7.31 (t, J = 7.6 Hz, 1 H), 7.40 (d, J = 8.8 Hz, 2 H), 7.57 (d, J = 8 Hz, 2 H), 7.80 (d, J = 10 Hz, 2 H), 10.62 (br, 1 H) ppm. ¹³C NMR (100 MHz, DMSO-d ₆): δ = 119.6, 119.8, 121.6, 123.0, 125.8, 126.4, 129.3, 130.5, 140.0, 152.4, 161.7 ppm. ESI-HRMS: m/z calcd for [C₁₃H₉ClN₂S + H]⁺: 260.0175; found: 260.0183. Compound 2h: ¹H NMR (400 MHz, DMSO-d ₆): δ = 2.35 (s, 3 H), 7.14 (d, J = 8.2 Hz, 1 H), 7.49–7.54 (m, 3 H), 7.62 (s, 1 H), 7.79 (d, J = 8.8 Hz, 2 H), 10.53 (br, 1 H) ppm. ¹³C NMR (100 MHz, DMSO-d ₆): δ = 21.3, 113.5, 119.5, 119.9, 121.5, 127.5, 130.5, 132.1, 132.3, 10.5, 150.3, 160.9 ppm. ESI-HRMS: m/z calcd for [C₁₄H₁₁BrN₂S + H]⁺: 318.9905; found: 318.9937. Compound 2t: ¹H NMR (400 MHz, CDCl₃): δ = 1.15–1.41 (m, 5 H), 1.51–1.56 (m, 1 H), 1.67–1.73 (m, 2 H), 2.05–2.30 (m, 2 H), 2.66–2.69 (m, 1 H), 3.50 (br s, 1 H), 6.99 (t, J = 2.4, 9.3 Hz, 1 H), 7.27 (dd, J = 2.4, 7.8 Hz, 1 H), 7.42 (dd, J = 4.9, 8.8 Hz, 1 H) ppm. ¹³C NMR (100 MHz, CDCl₃): δ = 24.7, 25.5, 33.5, 57.6, 121.1, 121.3, 123.6, 128.9, 136.9, 152.4, 165.7 ppm. ESI-HRMS: m/z calcd for [C₁₃H₁₆N₂S + H]⁺: 233.1112; found: 233.1140