Six-Membered Cyclic Amidines as Efficient Catalysts for the Synthesis of Cyclic Dithiocarbonates from Carbon Disulfide and Epoxides under Mild Conditions

Abstract

Six-membered cyclic amidines effectively catalyzed the reaction of carbon disulfide with epoxides under mild conditions, such as atmospheric pressure and ambient temperature, to give the corresponding cyclic dithiocarbonates (1,3-oxathiolane-2-thiones) in high yields.

Key words

amidines - organocatalysis - carbon disulfide - epoxides - cyclic dithiocarbonates - oxathiolanethiones

• References and Notes

• 1 New address: Molecular Engineering Institute, Kyushu Institute of Technology, 1-1 Sensui-cho, Tobata, Kitakyushu, Fukuoka 804-8550, Japan.
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• 21 1-Ethyl-2-methyl-4,5-dihydro-1H-imidazole (1c) N,N-Dimethylacetamide dimethyl acetal (90% purity; 8.14 g, 55 mmol) was added to a mixture of N-ethylethane-1,2-diamine (4.41 g, 50 mmol) in anhyd toluene (50 mL) at rt, and the mixture was stirred at 80 °C for 24 h. The mixture was concentrated in vacuo, and the residue was distilled under reduced pressure to give a colorless liquid; yield: 5.27 g (94%); bp 56–58 °C at 1.0 kPa. ¹H NMR (400 MHz, CDCl₃, 25 °C): δ = 1.13 (t, J = 7.2 Hz, 3 H, CH₂CH₃ ), 1.91 (s, 3 H, CH₃ ), 3.14 (q, J = 7.2 Hz, 2 H, CH₂ CH₃), 3.27 (t, J = 9.6 Hz, 2 H, CH₂CH₂ ), 3.63 (t, J = 9.4 Hz, 2 H, CH₂ CH₂). ¹³C NMR (100 MHz, CDCl₃, 25 °C): δ = 13.4 (CH₂ CH₃), 14.0 (CH₃), 41.1 (CH₂CH₃), 49.0 (CH₂CH₂), 51.6 (CH₂ CH₂), 164.3 (N=C–N). EI-MS: m/z = 112 [M⁺].
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• 23 The pK _a values were calculated by using: ACD/Labs Software, Version 11.02. Advanced Chemistry Development, Inc; Toronto: 2019
• 24 Cyclic Dithiocarbonates (3a–d); General Procedure A mixture of CS₂ (2 mmol) and 1a (0.01–0.03 mmol) was stirred at 25 °C for 10 min, and then a dilute solution of the appropriate epoxide 2a–d (1 mmol) in toluene or p-xylene (1 mL) was added dropwise to the mixture. The resulting mixture was stirred at 25 °C for 24 h then diluted with CHCl₃ (2 mL) and washed with H₂O (3 × 2 mL). The aqueous phase was extracted with CHCl₃ (2 mL), and the combined organic layers were dried (Na₂SO₄) and concentrated in vacuo. The residue was purified by column chromatography [silica gel, hexane–acetone (8:1 or 5:1)]. The first (minor) fraction was the cyclic trithiocarbonate (yellow oil or solid) byproduct 4a–d and the second (major) fraction was the cyclic dithiocarbonate major product 3a–d (pale-yellow oil). 5-(Phenoxymethyl)-1,3-oxathiolane-2-thione (3a) Pale-yellow oil; yield: 221 mg (98%). ¹H NMR (400 MHz, CDCl₃, 25 °C): δ = 3.75 (dd, J = 11.4, 7.4 Hz, 1 H, OCHCHHS), 3.81 (dd, J = 11.0, 7.8 Hz, 1 H, OCHCHHS), 4.29 (dd, J = 10.0, 4.8 Hz, 1 H, PhOCHH), 4.33 (dd, J = 10.0, 5.6 Hz, 1 H, PhOCHH), 5.41–5.48 (m, 1 H, OCHCH₂S), 6.90–6.95 (m, 2 H, 2-Ph-H, 6-Ph-H), 6.99–7.04 (m, 1 H, 4-Ph-H), 7.29–7.34 (m, 1 H, 3-Ph-H, 5-Ph-H). ¹³C NMR (100 MHz, CDCl₃, 25 °C): δ = 36.3 (OCHCH₂S), 66.2 (PhOCH₂), 87.7 (OCHCH₂S), 114.5 (2-Ph, 6-Ph), 121.9 (4-Ph), 129.7 (3-Ph, 5-Ph), 157.7 (1-Ph), 211.2 (C=S). EI-HRMS: m/z [M⁺] calcd for C₁₀H₁₀O₂S₂: 226.0122; found: 226.0123. 4-(Phenoxymethyl)-1,3-dithiolane-2-thione (4a) Yellow solid; mp (4.9 mg, 2%); mp 68–70 °C. ¹H NMR (400 MHz, CDCl₃, 25 °C): δ = 4.07 (dd, J = 12.2, 3.8 Hz, 1 H, SCHCHHS), 4.20 (dd, J = 10.2, 5.4 Hz, 1 H, SCHCHHS), 4.22 (dd, J = 12.2, 5.4 Hz, 1 H, PhOCHH), 4.37 (dd, J = 9.6, 9.6 Hz, 1 H, PhOCHH), 4.60–4.67 (m, 1 H, SCHCH₂S), 6.90–6.94 (m, 2 H, 2-Ph-H, 6-Ph-H), 6.99–7.04 (m, 1 H, 4-Ph-H), 7.29–7.34 (m, 2 H, 3-Ph-H, 5-Ph-H). ¹³C NMR (100 MHz, CDCl₃, 25 °C): δ = 44.9 (SCHCH₂S), 57.2 (SCHCH₂S), 66.5 (PhOCH₂), 114.6 (2-Ph, 6-Ph), 121.9 (4-Ph), 129.7 (3-Ph, 5-Ph), 157.7 (1-Ph), 226.4 (C=S). EI-HRMS: m/z [M⁺] calcd for C₁₀H₁₀OS₃: 241.9894; found: 241.9891. (2-Thioxo-1,3-oxathiolan-5-yl)methyl Methacrylate (3b) Pale-yellow oil; yield: 202 mg (93%). ¹H NMR (400 MHz, CDCl₃, 25 °C): δ = 1.97 (br s, 3 H, CH₃ ), 3.59 (dd, J = 11.2, 8.0 Hz, 1 H, OCHCHHS), 3.72 (dd, J = 11.4, 7.5 Hz, 1 H, OCHCHHS), 4.48 (dd, J = 12.4, 5.2 Hz, 1 H, CO₂CHH), 4.54 (dd, J = 12.4, 4.0 Hz, 1 H, CO₂CHH), 5.36–5.42 (m, 1 H, OCHCH₂S), 5.67 (quin, J = 1.4 Hz, 1 H, C = CHH), 6.18–6.20 (m, 1 H, C=CHH). ¹³C NMR (100 MHz, CDCl₃, 25 °C): δ = 18.2 (CH₃), 36.0 (OCHCH₂S), 63.3 (CO₂ CH₂), 87.4 (OCHCH₂S), 127.2 (C=CH₂), 135.2 (C=CH₂), 166.6 (C=O), 210.9 (C=S). EI-HRMS: m/z [M⁺] calcd for C₈H₁₀O₃S₂: 218.0071; found: 218.0066. (2-Thioxo-1,3-dithiolan-4-yl)methyl Methacrylate (4b) Yellow oil; yield: 12 mg (5%). ¹H NMR (400 MHz, CDCl₃, 25 °C): δ = 1.97 (t, J = 1.2 Hz, 3 H, CH₃ ), 3.86 (dd, J = 12.4, 4.0 Hz, 1 H, SCHCHHS), 4.16 (dd, J = 12.2, 5.8 Hz, 1 H, SCHCHHS), 4.47 (dd, J = 11.2, 6.4 Hz, 1 H, CO₂CHH), 4.51 (dd, J = 11.4, 7.4 Hz, 1 H, CO₂CHH), 4.55–4.62 (m, 1 H, SCHCH₂S), 5.65–5.67 (m, 1 H, C=CHH), 6.15–6.18 (m, 1 H, C=CHH). ¹³C NMR (100 MHz, CDCl₃, 25 °C): δ = 18.2 (CH₃), 44.9 (SCHCH₂S), 56.9 (SCHCH₂S), 63.1 (CO₂ CH₂), 126.9 (C=CH₂), 135.4 (C=CH₂), 166.6 (C=O), 225.8 (C=S). EI-HRMS: m/z [M⁺] calcd for C₈H₁₀O₂S₃: 233.9843; found: 233.9843. 5-(Butoxymethyl)-1,3-oxathiolane-2-thione (3c) Pale-yellow oil (195 mg, 95%). ¹H NMR (400 MHz, CDCl₃, 25 °C): δ = 0.93 (t, J = 7.4 Hz, 3 H, CH₃ ), 1.38 (sext, J = 7.2 Hz, 2 H, CH₃CH₂ ), 1.53–1.61 (m, 2 H, CH₃CH₂CH₂ ), 3.53 (t, J = 6.4 Hz, 2 H, CH₂CH₂ O), 3.61 (dd, J = 11.2, 7.2 Hz, 1 H, OCHCHHS), 3.69 (dd, J = 10.8, 8.4 Hz, 1 H, OCHCHHS), 3.74 (dd, J = 11.0, 4.6 Hz, 1 H, CH₂CH₂OCHH), 3.80 (dd, J = 10.8, 5.2 Hz, 1 H, CH₂CH₂OCHH), 5.20–5.26 (m, 1 H, OCHCH₂S). ¹³C NMR (100 MHz, CDCl₃, 25 °C): δ = 13.8 (CH₃), 19.2 (CH₃ CH₂), 31.5 (CH₃CH₂ CH₂), 36.2 (SCHCH₂S), 69.2 (CH₂ CH₂O), 71.9 (CH₂CH₂OCH₂), 89.2 (OCHCH₂S), 211.9 (C=S). EI-HRMS: m/z [M⁺] calcd for C₈H₁₄O₂S₂: 206.0435: found; 206.0435. 5-(Butoxymethyl)-1,3-dithiolane-2-thione (4c) Yellow oil; yield: 6.8 mg (3%). ¹H NMR (400 MHz, CDCl₃, 25 °C): δ = 0.93 (t, J = 7.2 Hz, 3 H, CH₃ ), 1.37 (sext, J = 7.2 Hz, 2 H, CH₃CH₂ ), 1.53–1.61 (m, 2 H, CH₃CH₂CH₂ ), 3.46–3.55 (m, 2 H, CH₂CH₂ O), 3.63 (dd, J = 9.8, 5.8 Hz, 1 H, SCHCHHS), 3.81 (dd, J = 9.8, 9.0 Hz, 1 H, SCHCHHS), 3.95 (dd, J = 12.0, 4.4 Hz, 1 H, CH₂CH₂ OCHH), 4.07 (dd, J = 12.0, 5.8 Hz, 1 H, CH₂CH₂OCHH), 4.42–4.49 (m, 1 H, SCHCH₂S). ¹³C NMR (100 MHz, CDCl₃, 25 °C): δ = 13.8 (CH₃), 19.2 (CH₃ CH₂), 31.6 (CH₃CH₂ CH₂), 44.9 (SCHCH₂S), 58.2 (SCHCH₂S), 69.7 (CH₂ CH₂O), 71.4 (CH₂CH₂OCH₂), 227.5 (C=S). EI-HRMS: m/z [M⁺] calcd for C₈H₁₄OS₃: 222.0207: found; 222.0207. 5-Butyl-1,3-oxathiolane-2-thione (3d) Pale-yellow oil; yield: 162 mg (92%). ¹H NMR (400 MHz, CDCl₃, 25 °C): δ = 0.94 (t, J = 7.2 Hz, 3 H, CH₃ ), 1.35–1.58 (m, 4 H, CH₃CH₂ CH₂ ), 1.78–1.88 (m, 1 H, CH₃CH₂CH₂CHH), 1.98–2.07 (m, 1 H, CH₃CH₂CH₂CHH), 3.41 (dd, J = 11.4, 9.4 Hz, 1 H, OCHCHHS), 3.60 (dd, J = 11.2, 6.4 Hz, 1 H, OCHCHHS), 5.07–5.15 (m, 1 H, OCHCH₂S). ¹³C NMR (100 MHz, CDCl₃, 25 °C): δ = 13.8 (CH₃), 22.3 (CH₃ CH₂), 27.4 (CH₃CH₂ CH₂), 33.4 (CH₃CH₂CH₂ CH₂), 39.3 (OCHCH₂S), 91.8 (OCHCH₂S), 212.2 (C=S). EI-HRMS: m/z [M⁺] calcd for C₇H₁₂OS₂: 176.0330: found; 176.0332. 4-Butyl-1,3-dithiolane-2-thione (4d) Yellow oil; yield: 8.0 mg (4%). ¹H NMR (400 MHz, CDCl₃, 25 °C): δ = 0.93 (t, J = 7.0 Hz, 3 H, CH₃ ), 1.34–1.47 (m, 4 H, CH₃CH₂ CH₂ ), 1.86–2.01 (m, 2 H, CH₃CH₂CH₂CH₂ ), 3.71 (dd, J = 12.0, 8.0 Hz, 1 H, SCHCHHS), 3.96 (dd, J = 11.8, 5.4 Hz, 1 H, SCHCHHS), 4.35–4.43 (m, 1 H, SCHCH₂S). ¹³C NMR (100 MHz, CDCl₃, 25 °C): δ = 13.8 (CH₃), 22.3 (CH₃ CH₂), 30.4 (CH₃CH₂ CH₂), 33.2 (CH₃CH₂CH₂ CH₂), 48.2 (SCHCH₂S), 60.9 (SCHCH₂S), 227.9 (C=S). EI-HRMS: m/z [M⁺] calcd for C₇H₁₂S₃: 192.0101: found; 192.0101.