4.2. Synthesis of Compounds 2a–i

A mixture of the appropriate 2-chloropyridine 1 (5 mmol), PdCl₂(PPh₃)₂ (0.17 g; 5 mol-%), and Et₃N (1.01 g; 10 mmol) was suspended in anhydrous THF (20 mL). The appropriate acetylene (5.5 mmol) was then injected under argon, followed by addition of CuI (0.02 g; 2.5 mol-%). The reaction mixture was stirred under argon at 40 °C temperature until full completion (1–3 h, completion observed by TLC). Solvent was evaporated under the reduced pressure; the crude residue was purified by column chromatography (elution by chloroform).

3,5-Dinitro-2-(phenylethynyl)pyridine (2a). 72%. Orange powder. M.p. 183–185 °C. ¹H NMR (300 MHz, CDCl₃): δ 7.45–7.54 (m, 3H, Ph_.), 7.74–7.76 (d, J = 7.2 Hz, 2H, Ph), 9.17 (s, 1H, H4), 9.63 (s, 1H, H6). ¹³C NMR (75 MHz, DMSO-d₆): δ 85.1, 100.9, 119.9, 128.7, 129.2, 131.3, 132.4, 142.3, 146.2, 148.3. HRMS (ESI) calc. for [C₁₃H₈N₃O₄]⁺ [M + H]⁺ 270.0509, found 270.0514.

3,5-Dinitro-2-(p-tolylethynyl)pyridine (2b). 63%. Orange powder. M.p. 203–205 °C. ¹H NMR (300 MHz, CDCl₃): δ 2.46 (s, 3H, Me), 7.30 (d, J = 8.0 Hz, 2H, p-Tolyl), 7.66 (d, J = 8.0 Hz, 2H, p-Tolyl), 9.18 (d, J = 2.2 Hz, 1H, H4), 9.63 (d, J = 2.2 Hz, 1H, H6). ¹³C NMR (75 MHz, DMSO-d₆): δ 21.3, 84.9, 101.6, 116.8, 128.6, 129.8, 132.4, 139.8, 141.7, 142.1, 146.0, 148.3. HRMS (ESI) calc. for [C₁₄H₁₀N₃O₄]⁺ [M + H]⁺ 284.0666, found 284.0669.

3,5-Dinitro-2-((4-fluorophenyl)ethynyl)pyridine (2c). 61%. Orange powder. M.p. 170–172 °C. ¹H NMR (200 MHz, DMSO-d₆): δ 7.40 (t, J = 8.5 Hz, 2H, 4F-Ph), 7.78 (dd, J = 7.9, 5.7 Hz, 2H, 4F-Ph), 9.21 (d, J = 2.2 Hz, 1H, H4), 9.65 (d, J = 2.2 Hz, 1H, H6). ¹³C NMR (75 MHz, DMSO-d₆): δ 85.0, 99.8, 128.8, 116.7 (d, ²J_C–F = 22.5 Hz), 116.6, 116.0, 130.6, 135.2 (d, ³J_C–F = 9.2 Hz), 139.6, 142.3, 146.1, 147.2, 148.4, 163.5 (d, ¹J_C–F = 251.5 Hz). HRMS (ESI) calc. for [C₁₃H₇FN₃O₄]⁺ [M + H]⁺ 288.0415, found 288.0417.

2-(Cyclopropylethynyl)-3,5-dinitropyridine (2d). 84%. Orange powder. M.p. 128–130 °C. ¹H NMR (300 MHz, CDCl₃): δ 1.09–1.18 (m, 4H), 1.68 (dt, J = 13.1, 6.6 Hz, 1H), 9.08 (d, J = 2.1 Hz, 1H, H4), 9.53 (d, J = 2.1 Hz, 1H, H6). ¹³C NMR (75 MHz, DMSO-d₆): δ 0.4, 9.9, 72.1, 109.5, 128.4, 141.7, 148.0. HRMS (ESI) calc. for [C₁₀H₈N₃O₄]⁺ [M + H]⁺ 234.0509, found 234.0517.

2-(Cyclopentylethynyl)-3,5-dinitropyridine (2e). 32%. Orange oil. ¹H NMR (300 MHz, CDCl₃): δ 1.75–1.64 (m, 2H), 1.87 (m, 4H), 2.10 (m, 2H), 3.04 (p, J = 7.2 Hz, 1H), 9.08 (d, J = 2.1 Hz, 1H, H4), 9.55 (d, J = 2.1 Hz, 1H, H6). ¹³C NMR (75 MHz, CDCl₃): δ 25.3, 31.2, 33.2, 76.5, 112.5, 127.9, 141.3, 142.0, 146.1, 147.7. HRMS (ESI) calc. for [C₁₂H₁₂N₃O₄]⁺ [M + H]⁺ 262.0822, found 262.0816.

2-(Hept-1-yn-1-yl)-3,5-dinitropyridine (2f). 35%. Orange oil. ¹H NMR (300 MHz, CDCl₃): δ 0.78–1.06 (m, 3H), 1.25–1.55 (m, 4H), 1.74 (p, J = 7.0 Hz, 2H), 2.63 (t, J = 7.1 Hz, 2H), 9.08 (d, J = 2.1 Hz, 1H, H4), 9.56 (d, J = 2.1 Hz, 1H, H6). ¹³C NMR (75 MHz, CDCl₃): δ 14.0, 20.4, 22.3, 27.5, 31.2, 108.8, 112.6, 128.0, 128.4, 141.5, 142.2, 147.8 HRMS (ESI) calc. for [C₁₂H₁₄N₃O₄]⁺ [M + H]⁺ 264.0979, found 264.0970.

Methyl-5-nitro-6-(phenylethynyl)nicotinate (2g) 76%. Orange powder. M.p. 117–119 °C. ¹H NMR (300 MHz, CDCl₃): δ 4.05 (s, 3H, Me), 7.42–7.52 (m, 3H, Ph.), 7.71–7.74 (d, J = 7.2 Hz, 2H, Ph), 8.95 (d, J = 1,3 Hz, 1H, H4), 9.39 (d, J = 1.3 Hz, 1H, H6). ¹³C NMR (75 MHz, CDCl₃): δ 53.2, 85.4, 101.4, 121.0, 125.0, 128.7, 130.7, 133.0, 133.5, 140.5, 146.5, 153.9, 163.5. HRMS (ESI) calc. for [C₁₅H₁₁N₂O₄]⁺ [M + H]⁺ 283.0713, found 283.0721.

3-Nitro-2-(phenylethynyl)-5-(trifluoromethyl)pyridine (2h) 42% Yellow powder. M.p. 124–126 °C. ¹H NMR (300 MHz, CDCl₃): δ 7.47 (m, 3H, Ph), 7.73 (d, J = 6.5 Hz, 2H, Ph), 8.65 (s, 1H, H4), 9.09 (s, 1H, H6). ¹³C NMR (126 MHz, CDCl₃): δ 84.8, 101.5, 120.9, 124.4 (q, ¹J_C–F = 273.0 Hz), 125.8, 128.8, 130.4 (q, ³J_C–F = 3.7 Hz), 131.0, 133.1, 140.6, 146.1, 149.9 (q, ³J_C–F = 3.5 Hz). HRMS (ESI) calc. for [C₁₄H₈F₃N₂O₂]⁺ [M + H]⁺ 293.0532, found 293.0542.

5-Chloro-3-nitro-2-(phenylethynyl)pyridine (2i) 40%. M.p. 103–105 °C. ¹H NMR (300 MHz, CDCl₃): δ 7.41–7.48 (m, 3H, Ph_.), 7.69–7.71 (d, J = 6.8 Hz, 2H, Ph), 8.41 (d, J = 1.6 Hz, 1H, H4), 8.81 (d, J = 1.6 Hz, 1H, H6). ¹³C NMR (75 MHz, CDCl₃): δ 84.5, 99.3, 121.3, 128.7, 130.4, 130.9, 132.3, 132.8, 135.5, 152.7. HRMS (ESI) calc. for [C₁₃H₈ClN₂O₂]⁺ [M + H]⁺ 259.0269, found 259.0259.