Synthesis and Characterization of THC Derivatives

Supporting Information (see footnote on the first page of this article): copies of 1D and 2D NMR spectra and extensive NMR studies are provided in Supporting Information.
1. General information: NMR spectra were recorded on a Bruker Avance III 400 MHz or a Bruker 500 MHz spectrometer and the compounds were assigned using ¹H NMR, ¹³C NMR, ¹¹B NMR, ¹⁹F NMR, COSY, HSQCED and HMBC spectra. Chemical shifts were reported in parts per million (ppm.) relative to reference (CDCl₃: ¹H: 7.26 ppm. and ¹³C 77.16 ppm; CD₃OD: ¹H: 3.31 ppm. and ¹³C 49.00 ppm; (CD₃)₂SO: ¹H: 2.50 ppm. and ¹³C 39.52 ppm.) NMR data are presented in the following way: chemical shift, multiplicity (s = singlet, bs = broad singlet, d = doublet, t = triplet, dd = doublet of doublets, ddd = doublet of doublet of doublets, dtd = doublet of triplet of doublets h = heptet, m = multiplet and/or multiple resonances) and coupling constants J in Hz. Reactions were monitored using TLC F₂₅₄ (Merck KGaA) using UV absorption detection (254 nm) and by spraying them with cerium ammonium molybdate stain (Hannesian's stain) followed by charring at ca 300 °C. Mass spectra were recorded on a JEOL AccuTOF CS JMS‐T100CS (ESI) mass spectrometer. Melting points (m.p.) were determined using a Büchi Melting Point B‐545. Automatic flash column chromatography was executed on a Biotage Isolera Spektra One using SNAP or Silicycle cartridges (Biotage, 30–100 μm, 60Å) 4–50 g. Reactions under protective atmosphere were performed under positive Ar./N₂ flow in flame‐dried flasks. Atom‐numbering of the THC compounds is derived from an earlier reported NMR assignment in literature.192. General proceduresGeneral procedure I for potassium trifluoroborate salt synthesis from boronic acid (22–25):21 Boronic acid (1 equiv.) was dissolved in acetonitrile (0.1M), KF (4 equiv.) in water (1M) was added at r.t. and the reaction was left stirring for 5 min. 2,3‐Dihydroxysuccinic acid (2.05 equiv.) dissolved in THF (0.3M) (heat was required) was added dropwise to the vigorously stirred biphasic mixture and a white precipitate formed immediately. The reaction was diluted with acetonitrile and filtered. The flask and filter were rinsed with acetonitrile and the filtrate was concentrated in vacuo. The residue was dried under high vacuum affording the trifluoroborate salt as pure product (22–25).
General procedure II for sp²‐sp² Suzuki Miyaura coupling (10a–c, 11a–c):10 Cs₂CO₃ (3 equiv.), PdCl₂(dppf) (5 mol‐%) and the trifluoroborate salt (1.6 equiv.) were added in a flask which was evacuated and backfilled thrice with Ar. Bromo‐(–)‐trans‐Δ⁸‐tetrahydrocannabinol (6)/(7) (1 equiv.) was added in dry MeOH (0.1M) and the reaction was stirred at 65 °C. After 16 h the mixture was cooled to r.t. and diluted with Et₂O. The mixture was filtered through Celite, dried with MgSO₄, concentrated in vacuo and purified through silica gel column chromatography or preparative HPLC to afford the product (10a–c, 11a–c).
General procedure III for sp²‐sp³ Suzuki Miyaura coupling (12a–12b, 13a–13b):20 Bromo‐(–)‐trans‐Δ⁸‐tetrahydrocannabinol (6)/(7) (1 equiv.) was dissolved in toluene (0.2M) and Pd(OAc)₂ (10 mol‐%), RuPhos (20 mol‐%), alkyl trifluoroborate salt (1.5 equiv.) and aqueous sodium hydroxide (3M, 3 equiv.) were added. The reaction mixture was stirred at 120 °C and followed with TLC until full conversion (± 64 h) after which it was diluted with aqueous hydrochloric acid (1M) and DCM. The mixture was extracted with DCM and the combined organic layers were filtered through Celite, dried with MgSO₄, concentrated in vacuo and purified through silica gel column chromatography or preparative HPLC to afford the product (12a, 12b, 13a, 13b).
3. Experimental details and analysis5‐Propylbenzene‐1,3‐diol (1c):23 1‐Bromo‐3,5‐dimethoxybenzene (400 mg, 1.84 mmol) was dissolved in dry toluene. n‐Propylboronic acid (21) (243 mg, 2.76 mmol), PdCl₂(dppf) (5 mol‐%) and potassium phosphate (1.17 g, 5.53 mmol) were added and the flask was evacuated and backfilled with argon thrice. The reaction was stirred at 110 °C for 16 h. The mixture was cooled to r.t. and diluted with Et₂O after which it was filtered through Celite, dried with MgSO₄ and concentrated in vacuo, the crude 1,3‐dimethoxy‐5‐propylbenzene was directly used in the next step. The product was dissolved in dry DCM (20 mL) and kept under protective atmosphere. The solution was cooled to 0 °C and boron tribromide (455 µL, 4.79 mmol) was carefully added dropwise. The reaction was left stirring for 16 h and warmed‐up to r.t. The reaction was cooled to 0 °C before saturated aqueous NaHCO₃ (15 mL) was added. After no more gas evolution was observed NaOH (3M, 5 mL) was added. The mixture was extracted with DCM (2 × 50 mL) and EtOAc (2 × 50 mL) and the resulting aqueous phase was acidified with HCl (1M) until pH 2. The aqueous layer was washed again with DCM (2 × 50 mL) and EtOAc (2 × 50 mL). The combined organic layers were dried with MgSO₄, concentrated in vacuo and purified by silica gel column chromatography (0→30 % EtOAc in n‐heptane) to afford 14 (168 mg, 60 % over two steps) as a green oil. TLC (EtOAc/n‐heptane, 3:7 v/v): R_f = 0.28. ¹H‐NMR (400 MHz, CDCl₃) δ 6.25 (d, J = 2.2 Hz, 2H), 6.18 (t, J = 2.3 Hz, 1H), 4.93 (s, 2H), 2.50–2.41 (m, 2H), 1.66–1.54 (m, 2H), 0.92 (t, J = 7.3 Hz, 3H). ¹³C NMR (100 MHz, CDCl₃) δ 156.66, 146.06, 108.28, 100.34, 38.02, 24.26, 13.93. HRMS (m/z): [M + H]⁺ calcd. for C₉H₁₂O₂: 152.08373, found 152.08270.
4′‐Hydroxyl‐(–)‐trans‐Δ⁸‐tetrahydrocannabinol (3): Benzene‐1,3,5‐triol (1b, 9.94 g, 78.8 mmol) was dissolved in dry Et₂O (200 mL) and stirred vigorously. (S)‐cis‐verbenol (4.00 g, 26.3 mmol) was added and the reaction was stirred at r.t. Trifluoromethanesulfonic acid (581 µL, 6.60 mmol) was added dropwise at –10 °C and the reaction was left stirring for 4 h. To stop the reaction saturated aqueous NH₄Cl (100 mL) was added and the mixture was extracted with Et₂O (2 × 100 mL). The combined organic layers were dried with MgSO₄, concentrated in vacuo and purified by silica gel column chromatography (0→50 % EtOAc in n‐heptane) to give 3 (3.61 g, 53 %) as a yellow solidified oil. TLC (EtOAc/n‐heptane, 1:1 v/v): R_f = 0.60. ¹H NMR (400 MHz, CDCl₃) δ 5.94–5.93 (m, 1H), 5.86 (d, J = 2.4 Hz, 1H), 5.41 (d, J = 4.8 Hz, 1H), 5.17 (bs, 2H), 3.14 (dd, J = 15.3, 4.0 Hz, 1H), 2.64 (td, J = 10.9, 4.7 Hz, 1H), 2.18–2.09 (m, 1H), 1.86–1.74 (m, 3H), 1.69 (s, 3H), 1.36 (s, 3H), 1.09 (s, 3H). ¹³C NMR (100 MHz, CDCl₃) δ 156.04, 155.82, 154.98, 134.85, 119.41, 106.45, 97.30, 96.05, 77.36, 45.01, 36.33, 31.45, 27.98, 27.60, 23.62, 18.62. HRMS (m/z): [M + H]⁺ calcd. for C₁₆H₂₀O₃: 261.14907, found 261.14737.
4′‐Triflate‐(–)‐trans‐Δ⁸‐tetrahydrocannabinol (4): 4′‐Hydroxyl‐(–)‐trans‐Δ⁸‐tetrahydrocannabinol (3, 100 mg, 384 µmol) was dissolved in dry DCM (4 mL) and stirred at 0 °C before 2,6‐dimethylpyridine (36 µL, 311 µmol) was added. Trifluoromethanesulfonic anhydride (52 µL, 311 µmol) was added over a course of 10 min. After 14 h the reaction was diluted with DCM (10 mL) and washed with water (4 mL), HCl (1M, 4 mL), saturated aqueous NaHCO₃ (3 mL) and brine (3 mL). The organic layer was dried with MgSO₄, concentrated in vacuo and purified by silica gel column chromatography (0→25 % EtOAc in n‐heptane) to afford 4 (58.9 mg, 56 %, based on recovery of SM) as a yellow oil. TLC (EtOAc/n‐heptane, 1:1 v/v): R_f = 0.79. ¹H NMR (400 MHz, CDCl₃) δ 6.37 (d, J = 2.5 Hz, 1H), 6.23 (d, J = 2.5 Hz, 1H), 5.47–5.41 (m, 1H), 5.21 (s, 1H), 3.20–3.10 (m, 1H), 2.70 (td, J = 11.0, 4.8 Hz, 1H), 2.20–2.10 (m, 1H), 1.89–1.76 (m, 3H), 1.71 (s, 3H), 1.39 (s, 3H), 1.10 (s, 3H). ¹³C NMR (100 MHz, CDCl₃) δ 156.15, 155.84, 148.26, 134.54, 119.43, 113.81, 103.63, 100.81, 78.02, 44.64, 35.68, 31.67, 27.89, 27.49, 23.56, 18.64. ¹⁹F NMR (377 MHz, CDCl₃) δ –72.93. HRMS (m/z): [M + H]⁺ calcd. for C₁₇H₁₉F₃O₅S: 393.09835, found 393.10073.
5‐Bromobenzene‐1,3‐diol (5):24 1‐Bromo‐3,5‐dimethoxybenzene (5.00 g, 23.0 mmol) was dissolved in dry DCM (100 mL) and kept under protective atmosphere. The solution was cooled to 0 °C and boron tribromide (7.62 mL, 80.62 mmol) was added carefully dropwise. The reaction was left stirring for 16 h and warmed to r.t. The reaction was cooled to 0 °C before saturated aqueous NaHCO₃ (70 mL) was added. After no more gas evolution was observed NaOH (1M, 5 mL) was added. The mixture was extracted with DCM (2 × 100 mL) and EtOAc (2 × 100 mL) and the resulting aqueous phase was acidified with HCl (1M) until pH 2. The aqueous layer was extracted again with DCM (3 × 100 mL) and EtOAc (3 × 100 mL). The combined organic layers were dried with MgSO₄, concentrated in vacuo and purified through silica gel column chromatography (0→30 % EtOAc in n‐heptane) to afford 5 (4.35 g, 100 %) as a brown solid. TLC (EtOAc/n‐heptane, 3:7 v/v): R_f = 0.20. ¹H‐NMR (400 MHz, CDCl₃) δ 6.59 (d, J = 2.2 Hz, 2H), 6.28 (t, J = 2.2 Hz, 1H), 5.15 (s, 2H). ¹³C NMR (100 MHz, CDCl₃) δ 157.76, 122.97, 111.56, 102.21. m.p. 86.9 °C.
2′‐Bromo‐(–)‐trans‐Δ⁸‐tetrahydrocannabinol (6): 5‐Bromobenzene‐1,3‐diol (5, 1.35 g, 7.14 mmol) was dissolved in dry DCM (100 mL) and stirred vigorously. (S)‐cis‐verbenol (1.09 g, 7.14 mmol) was added and the reaction was stirred at r.t. Trifluoromethanesulfonic acid (284 µL, 3.21 mmol) was added dropwise at 0 °C and the reaction was left stirring for 20 h. To stop the reaction saturated aqueous NaHCO₃ (50 mL) was added and the mixture was extracted with DCM (2 × 100 mL). The combined organic layers were dried with MgSO₄, concentrated in vacuo and purified through silica gel column chromatography (0→4 % EtOAc in n‐heptane) to afford 6 (1.32 g, 57 %) as a yellow oil and 7 as a minor product (199 mg, 9 %). TLC (EtOAc/n‐heptane, 1:9 v/v): R_f = 0.23. ¹H NMR (400 MHz, CDCl₃) δ 6.68 (d, J = 2.6 Hz, 1H), 6.28 (d, J = 2.6 Hz, 1H), 5.46–5.41 (m, 1H), 5.05 (s, 1H), 3.41 (dd, J = 16.4, 3.4 Hz, 1H), 2.64 (td, J = 10.5, 4.3 Hz, 1H), 2.18–2.11 (m, 1H), 1.86 (m, 3H), 1.71 (s, 3H), 1.37 (s, 3H), 1.07 (s, 3H). ¹³C NMR (100 MHz, CDCl₃) δ 155.81, 155.01, 134.84, 123.71, 119.64, 118.78, 113.64, 104.40, 77.51, 46.55, 36.80, 35.15, 28.41, 27.41, 23.56, 18.29. HRMS (m/z): [M + H]⁺ calcd. for C₁₆H₁₉BrO₂: 323.06467, found 323.06511. 4′‐Bromo‐(–)‐trans‐Δ⁸‐tetrahydrocannabinol (7): TLC (EtOAc/n‐heptane, 1:9 v/v): R_f = 0.35. ¹H NMR (400 MHz, CDCl₃) δ 6.61 (d, J = 1.9 Hz, 1H), 6.43 (d, J = 1.9 Hz, 1H), 5.46–5.40 (m, 1H), 5.24 (s, 1H), 3.16 (dd, J = 15.7, 4.4 Hz, 1H), 2.66 (td, J = 11.1, 4.8 Hz, 1H), 2.19–2.09 (m, 1H), 1.84–1.74 (m, 3H), 1.70 (s, 3H), 1.38 (s, 3H), 1.09 (s, 3H). ¹³C NMR (100 MHz, CDCl₃) δ 155.94, 155.79, 134.67, 119.77, 119.43, 113.82, 112.74, 110.84, 77.62, 44.81, 35.81, 31.70, 27.93, 27.53, 23.58, 18.58. HRMS (m/z): [M + H]⁺ calcd. for C₁₆H₁₉BrO₂: 323.06467, found 323.06620.
5‐Chlorobenzene1,3‐diol (8): 1‐Chloro‐3,5‐dimethoxybenzene (1.01 g, 5.85 mmol) was dissolved in ACN (12 mL) and kept under protective atmosphere. Iodotrimethylsilane (4.78 mL, 35.11 mmol) was added and the solution was heated to 70 °C. The reaction was left stirring overnight at reflux. The mixture was cooled to r.t. and concentrated in vacuo. The residue was dissolved in 1M aqueous HCl (10 mL) and DCM (15 mL), after which the aqueous layer was extracted with DCM (2 × 15 mL). The combined organic layers were dried with Na₂SO₄, concentrated in vacuo and purified using silica gel column chromatography (0→20 % EtOAc in n‐heptane) to afford 8 (222 mg, 26 %) as a yellow solidified oil. TLC (EtOAc/n‐heptane, 1:4 v/v): R_f = 0.20 ¹H‐NMR (500 MHz, CDCl₃) δ 6.44 (d, J = 2.2 Hz, 2H), 6.24 (s, 1H), 5.01 (s, 2H); ¹³C NMR (126 MHz, CDCl₃) δ 157.51, 135.23, 108.46, 101.52. m.p. 58.8 °C.
5‐Iodobenzene‐1,3‐diol (9): 3,5‐Dimethoxyiodobenzene (15, 0.867 g, 3.28 mmol) was dissolved in ACN (7 mL) and kept under protective atmosphere. Iodotrimethylsilane (2.80 mL, 19.7 mmol) was added and the solution was heated to 70 °C. The reaction was left stirring overnight at reflux. After cooling to r.t. the reaction mixture was concentrated in vacuo and the residue was dissolved in 1 M aqueous HCl (10 mL) and DCM (15 mL). The aqueous layer was extracted with DCM (2 × 15 mL), the combined organic layers were dried with Na₂SO₄, concentrated in vacuo and purified with silica gel column chromatography (0→20 % EtOAc in n‐heptane) to afford 9 (198 mg, 26 %, based on recovery of SM) as a brown solid. TLC (EtOAc/n‐heptane, 1:1 v/v): R_f = 0.50; ¹H NMR (400 MHz, CDCl₃) δ 6.79 (d, J = 2.2 Hz, 2H), 6.31 (t, J = 2.2 Hz, 1H), 5.22 (s, 2H). ¹³C NMR (100 MHz, CDCl₃) δ 157.42, 117.59, 103.01, 93.80. m.p. 74.1 °C.
2′‐Styrene(–)‐trans‐Δ⁸‐Tetrahydrocannabinol (10a): Synthesized according to general procedure II from 2′‐bromo‐(–)‐trans‐Δ⁸‐tetrahydrocannabinol (6, 88.3 mg, 258 µmol) and potassium (E)‐styryl trifluoroborate (86.6 mg, 412 µmol) which afforded (10a, 69.2 mg, 78 %) as a colorless oil. TLC (EtOAc/n‐heptane, 1:9 v/v): R_f = 0.11. ¹H NMR (500 MHz, CDCl₃) δ 7.51–7.47 (m, 2H), 7.37 (t, J = 7.7 Hz, 2H), 7.29–7.26 (m, 1H), 7.19 (d, J = 16.0 Hz, 1H), 6.93 (d, J = 16.0 Hz, 1H), 6.66 (d, J = 2.6 Hz, 1H), 6.28 (d, J = 2.6 Hz, 1H), 5.45 (m, 1H), 4.79 (bs, 1H), 2.83 (td, J = 10.8, 4.5 Hz, 1H), 2.71–2.64 (m, 1H), 2.23–2.15 (m, 1H), 1.89–1.80 (m, 2H), 1.62 (s, 3H), 1.40 (s, 3H), 1.14 (s, 3H). ¹³C NMR (126 MHz, CDCl₃) δ 155.14, 154.84, 138.54, 137.62, 134.88, 128.97, 128.90, 128.24, 127.77, 126.65, 119.99, 117.32, 106.33, 103.98, 76.73, 46.01, 39.69, 33.10, 28.42, 27.59, 23.74, 18.38. HRMS (m/z): [M + H]⁺ calcd. for C₂₄H₂₆O₂: 347.20110, found 347.20075.
2′‐Naphthalene(–)‐trans‐Δ⁸‐tetrahydrocannabinol (10b‐S_a and 10b‐R_a): Synthesized according to general procedure II from 2′‐bromo‐(–)‐trans‐Δ⁸‐tetrahydrocannabinol (6) (150 mg, 464 µmol) and potassium (1‐naphthalene) trifluoroborate (24, 174 mg, 743 µmol) and purified using preparative HPLC to afford (10b, 28.5 mg, 17 %) as a colorless oil. The product was obtained as an inseparable mixture of two atropisomers 10b‐R_a and 10b‐S_a in ratios of 0.64:1.00, respectively. TLC (EtOAc/n‐heptane, 1:9 v/v): R_f = 0.15. 10b‐R_a:¹H NMR (500 MHz, [D₆]DMSO) δ 7.94 (d, J = 8.2 Hz, 1H), 7.81 (d, J = 7.9 Hz, 1H), 7.56 (dd, i = 6.8, 1.6 Hz, 1H), 7.56–7.52 (m, 1H), 7.45–7.43 (m, 1H), 7.41–7.39 (m, 1H), 7.32 (dd, J = 7.1, 1.2 Hz, 1H), 6.23 (d, J = 2.6 Hz, 1H), 6.16 (d, J = 2.6 Hz, 1H), 5.18 (d, J = 2.7 Hz, 1H), 2.69 (dt, J = 11.2, 5.6 Hz, 1H), 2.04 (m, 1H), 1.77–1.67 (m, 1H), 1.58 (dd, J = 11.6, 4.4 Hz, 1H), 1.33 (s, 3H), 1.19 (s, 3H), 1.17 (s, 1H), 0.93 (d, J = 12.6 Hz, 1H), 0.92–0.86 (bs, 3H). ¹³C NMR (126 MHz, [D₆]DMSO) δ 156.09, 155.36, 140.94, 140.22, 133.93, 133.30, 132.06, 128.49, 127.63, 126.62, 126.36, 126.29, 125.92, 125.85, 119.94, 115.78, 111.97, 103.51, 76.41, 45.15, 36.65, 32.61, 27.75, 27.56, 23.14, 18.86. 10b‐S_a: ¹H NMR (500 MHz, [D₆]DMSO) δ 8.00–7.98 (m, 2H), 7.60 (dd, J = 8.3, 7.0 Hz, 1H), 7.51 (d, J = 1.5 Hz, 1H), 7.45 (m, 2H), 7.41–7.39 (m, 1H), 6.27 (d, J = 2.6 Hz, 1H), 6.25 (d, J = 2.6 Hz, 1H), 5.08 (d, J = 4.3 Hz, 1H), 2.16 (td, J = 10.7, 4.9 Hz, 1H), 1.97–1.93 (m, 1H), 1.55–1.53 (m, 2H), 1.32 (s, 3H), 1.31–1.29 (m, 1H), 1.18 (s, 3H), 1.06 (s, 3H), 0.97–0.90 (m, 1H). ¹³C NMR (126 MHz, [D₆]DMSO) δ 156.85, 154.69, 141.46, 141.14, 133.30, 133.26, 130.55, 128.83, 127.89, 126.93, 126.67, 126.45, 126.09, 125.41, 119.68, 115.84, 111.66, 103.65, 76.35, 45.01, 37.58, 33.44, 27.75, 27.56, 23.31, 18.90. HRMS (m/z): [M + H]⁺ calcd. for C₂₆H₂₆O₂: 371.20110, found 371.20214.
2′‐(4‐Methoxybenzene)‐(–)‐trans‐Δ⁸‐tetrahydrocannabinol (10c): Synthesized according to general procedure I from 2′‐bromo‐(–)‐trans‐Δ⁸‐tetrahydrocannabinol (6, 98.0 mg, 68 µmol) and potassium (4‐methoxyphenyl) trifluoroborate (25, 104 mg, 485 µmol) to afford 10c (24.0 mg, 23 %) as a colorless oil. TLC (EtOAc/n‐heptane, 1:9 v/v): R_f = 0.07. ¹H NMR (400 MHz, CDCl₃) δ 7.25 (d, J = 8.7 Hz, 2H), 6.92 (d, J = 8.7 Hz, 2H), 6.29 (d, J = 0.6 Hz), 5.28 (m, 1H), 4.72 (s, 1H), 3.85 (s, 3H), 2.86 (td, J = 10.9, 4.8 Hz, 1H), 2.13–2.06 (m, 1H), 1.76–1.69 (m, 2H), 1.58–1.52 (m, 1H), 1.45–1.40 (m, 1H), 1.38 (s, 3H), 1.35–1.33 (m, 3H), 1.22 (s, 3H). ¹³C NMR (126 MHz, CDCl₃) δ 158.70, 155.14, 154.35, 143.56, 135.50, 134.66, 129.10, 118.93, 116.34, 113.89, 110.62, 102.94, 76.41, 55.37, 45.11, 36.70, 32.68, 27.99, 27.50, 23.29, 18.34. HRMS (m/z): [M + H]⁺ calcd. for C₂₃H₂₆O₃: 351.19602, found 351.19571.
4′‐Styrene‐(–)‐trans‐Δ⁸‐tetrahydrocannabinol (11a): Synthesized according to general procedure II from 4′‐bromo‐(–)‐trans‐Δ⁸‐tetrahydrocannabinol (7, 20.0 mg, 62 µmol) and potassium (E)‐styryl trifluoroborate (21.0 mg, 99 µmol) to afford 11a (4.8 mg, 27 %) as a colorless oil. TLC (EtOAc/n‐heptane, 1:9 v/v): R_f = 0.27. ¹H NMR (500 MHz, CDCl₃) δ 7.49–7.45 (m, 2H), 7.34 (t, J = 7.7 Hz, 2H), 7.24 (m 1H), 7.02 (d, J = 16.3 Hz, 1H), 6.92 (d, J = 16.3 Hz, 1H), 6.62 (d, J = 1.6 Hz, 1H), 6.44 (d, J = 1.7 Hz, 1H3′), 5.45–5.43 (m, 1H), 4.81 (s, 1H), 3.21 (dd, J = 15.9, 4.5 Hz, 1H), 2.74 (td, J = 10.8, 4.7 Hz, 1H), 2.20–2.12 (m, 1H), 1.92–1.78 (m, 3H), 1.72 (s, 3H), 1.40 (s, 3H), 1.13 (s, 3H). ¹³C NMR (126 MHz, CDCl₃) δ 155.48, 155.31, 137.44, 137.04, 134.81, 128.80, 128.77, 128.21, 127.71, 126.64, 119.51, 113.30, 108.77, 105.63, 77.06, 44.99, 36.08, 31.98, 28.03, 27.71, 23.65, 18.68. HRMS (m/z): [M + H]⁺ calcd. for C₂₄H₂₆O₂: 347.20110, found 347.20105.
4′‐Naphthalene‐(–)‐trans‐Δ⁸‐tetrahydrocannabinol (11b): Synthesized according to general procedure II from 4′‐bromo‐(–)‐trans‐Δ⁸‐tetrahydrocannabinol (7, 25.0 mg, 77 µmol) and potassium (1‐naphthalene) trifluoroborate (24, 29.0 mg, 120 µmol) to afford 11b (17.1 mg, 60 %) as a colorless oil. TLC (EtOAc/n‐heptane, 1:9 v/v): R_f = 0.27. ¹H NMR (500 MHz, CDCl₃) δ 8.04 (d, J = 8.4 Hz, 1H), 7.87 (d, J = 8.0 Hz, 1H), 7.82 (d, J = 8.1 Hz, 1H), 7.51–7.44 (m, 2H), 7.44–7.39 (m, 2H), 6.59 (d, J = 1.7 Hz, 1H), 6.41 (d, J = 1.7 Hz, 1H), 5.49–5.47 (m, 1H), 4.98 (s, 1H), 3.30 (dd, J = 17.2, 4.7 Hz, 1H), 2.83 (td, J = 10.8, 4.8 Hz, 1H), 2.24–2.16 (m, 1H), 2.01–1.84 (m, 3H), 1.74 (s, 3H), 1.42 (s, 3H), 1.19 (s, 3H). ¹³C NMR (126 MHz, CDCl₃) δ 155.15, 154.85, 140.27, 139.85, 134.92, 133.90, 131.60, 128.29, 127.65, 126.69, 126.42, 126.01, 125.83, 125.44, 119.52, 112.43, 112.33, 109.44, 77.08, 45.10, 36.13, 31.95, 28.10, 27.75, 23.67, 18.76. HRMS (m/z): [M + H]⁺ calcd. for C₂₆H₂₆O₂: 371.20110, found 371.20176.
4′‐(4‐Methoxybenzene)‐(–)‐trans‐Δ⁸‐tetrahydrocannabinol (11c): Synthesized according to general procedure II from 4′‐bromo‐(–)‐trans‐Δ⁸‐tetrahydrocannabinol (7, 100 mg, 309 µmol) and potassium (4‐methoxyphenyl) trifluoroborate (25, 106 mg, 495 µmol) to afford 11c (31.0 mg, 29 %) as a colorless oil. TLC (EtOAc/n‐heptane, 1:9 v/v): R_f = 0.17. ¹H NMR (500 MHz, CDCl₃) 7.47 (d, J = 8.8 Hz, 2H), 6.93 (d, J = 8.8 Hz, 2H), 6.65 (d, J = 1.7 Hz, 1H), 6.48 (d, J = 1.8 Hz, 1H), 5.45 (d, J = 5.4 Hz, 1H), 4.87 (s, 1H), 3.83 (s, 3H), 3.23 (dd, J = 16.4, 4.5 Hz, 1H), 2.76 (td, J = 10.8, 4.6 Hz, 1H), 2.21–2.09 (m, 1H), 1.89–1.80 (m, 3H), 1.72 (s, 3H), 1.41 (s, 3H), 1.14 (s, 3H). ¹³C NMR (126 MHz, CDCl₃) δ 158.89, 155.55, 155.39, 143.91, 135.73, 134.85, 127.91, 119.51, 114.20, 112.61, 108.76, 105.89, 77.06, 55.46, 45.03, 36.12, 31.81, 28.05, 27.73, 23.65, 18.72. HRMS (m/z): [M + H]⁺ calcd. for C₂₃H₂₆O₃: 351.19602, found 351.19740.
Ortho‐n‐pentyl‐(–)‐trans‐Δ⁸‐tetrahydrocannabinol (12a): Synthesized according to general procedure III from 2′‐bromo‐(–)‐trans‐Δ⁸‐tetrahydrocannabinol (6, 77.9 mg, 241 µmol) and potassium n‐pentylboron trifluoride (23, 64.4 mg, 362 µmol). Silica gel column chromatography (0→8 % EtOAc/n‐heptane) afforded 12a (38.8 mg, 51 %) as an inseparable mixture with 6. TLC (EtOAc/n‐heptane, 1:9 v/v): R_f = 0.23. ¹H NMR (500 MHz, CDCl₃) δ 6.29 (d, J = 2.7 Hz, 1H), 6.16 (d, J = 2.6 Hz, 1H), 5.47–5.44 (m, 1H), 4.88 (s, 1H), 2.71–2.62 (m, 1H), 2.60–2.55 (m, 3H), 2.21–2.10 (m, 1H), 1.87–1.81 (m, 3H), 1.70 (s, 3H), 1.67–1.57 (m, 2H), 1.36 (s, 3H), 1.35–1.23 (m, 4H), 1.06 (s, 3H), 0.94–0.86 (m, 3H). ¹³C NMR (126 MHz, CDCl₃) δ 154.94, 154.55, 143.99, 134.64, 120.13, 117.21, 109.24, 102.19, 76.35, 46.63, 38.86, 33.53, 33.47, 32.07, 31.07, 28.49, 27.59, 23.61, 22.67, 18.25, 14.22. HRMS (m/z): [M + H]⁺ calcd. for C₂₁H₃₀O₂: 315.23240, found 315.23200.
2′‐Ortho‐n‐propyl‐(–)‐trans‐Δ⁸‐tetrahydrocannabinol (12b): Synthesized according to general procedure III from 2′‐bromo‐(–)‐trans‐Δ⁸‐tetrahydrocannabinol (6, 130 mg, 402 µmol) and potassium n‐propylboron trifluoride (22, 90.5 mg, 603 µmol). Silica gel column chromatography (0→8 % EtOAc/n‐heptane) afforded 12b (63.9 mg, 56 %) as an inseparable mixture with 6. TLC (Toluene): R_f = 0.05. ¹H NMR (500 MHz, CDCl₃) δ 6.29 (d, J = 2.8Hz, 1H), 6.16 (d, J = 2.7 Hz, 1H), 5.48–5.43 (m, 1H), 4.97–4.89 (m, 1H), 2.71–2.62 (m, 1H), 2.60 (m, 1H), 2.56 (t, J = 7.9 Hz, 2H), 2.18–2.10 (m, 1H), 1.88–1.79 (m, 3H), 1.70 (s, 3H), 1.65–1.59 (m, 2H), 1.36 (s, 3H), 1.06 (s, 3H), 0.96 (t, J = 7.3 Hz, 3H). ¹³C NMR (126 MHz, CDCl₃) δ 154.94, 154.56, 143.78, 134.65, 120.15, 117.28, 109.22, 102.24, 76.35, 46.65, 38.88, 35.62, 33.48, 28.50, 27.59, 24.54, 23.64, 18.25, 14.29. HRMS (m/z): [M + H]⁺ calcd. for C₁₉H₂₆O₂: 287.20110, found 287.20130.
(–)‐trans‐Δ⁸‐tetrahydrocannabinol (13a):9 5‐Pentylbenzene‐1,3‐diol (1a, 1.18 g, 6.60 mmol) and (S)‐cis‐verbenol (1.00 g, 6.60 mmol) were stirred at r.t. in dry DCM (70 mL). Trifluoromethanesulfonic acid (145 µL, 1.64 mmol) was added dropwise at 0 °C and the reaction was left stirring for 2 h. To stop the reaction saturated aqueous NaHCO₃ (70 mL) was added and the mixture was extracted with DCM (2 × 70 mL). The combined organic layers were dried with MgSO₄, concentrated in vacuo and purified through silica gel column chromatography (0→4 % EtOAc/n‐heptane) to afford 1 (691 mg, 33 %) as a yellow oil. TLC (EtOAc/n‐heptane, 1:9 v/v): R_f = 0.38. ¹H NMR (400 MHz, CDCl₃) δ 6.29 (d, J = 1.5 Hz, 1H), 6.11 (d, J = 1.5 Hz, 1H), 5.44 (d, J = 4.8 Hz, 1H), 4.93 (s, 1H) 3.22 (dd, J = 15.8, 4.2 Hz, 1H), 2.71 (td, J = 10.8, 4.6 Hz, 1H), 2.44 (td, J = 7.4, 2.0 Hz, 2H), 2.20–2.11 (m, 1H), 1.91–1.76 (m, 3H), 1.71 (s, 3H), 1.62–1.53 (m, 2H), 1.39 (s, 3H), 1.34–1.26 (m, 4H), 1.12 (s, 3H), 0.91–0.87 (m, 3H). ¹³C NMR (100 MHz, CDCl₃) δ 154.93, 154.92, 142.83, 134.89, 119.45, 110.70, 110.20, 107.83, 76.86, 45.05, 36.17, 35.59, 31.74, 31.72, 30.74, 28.04, 27.70, 23.63, 22.69, 18.63, 14.16. HRMS (m/z): [M + H]⁺ calcd. for C₂₁H₃₀O₂: 315.23240, found 315.23343.
(–)‐trans‐Δ⁸‐tetrahydrocannabinol (13a): Synthesized according to general procedure III from 4′‐bromo‐(–)‐trans‐Δ⁸‐tetrahydrocannabinol (7, 52.1 mg, 161 µmol) and potassium n‐pentylboron trifluoride (23, 43.0 mg, 242 µmol) to afford 13a (17.4 mg, 34 %) as a yellow oil. Spectral data were in agreement with previously synthesized 1 and hence no further purification was executed.
4′‐Propyl‐(–)‐trans‐Δ⁸‐tetrahydrocannabinol (13b): 5‐Propylbenzene‐1,3‐diol (1c, 150 mg, 986 µmol) and (S)‐cis‐verbenol (150 g, 986 µmol) were stirred at r.t. in dry DCM (20 mL). Trifluoromethanesulfonic acid (26.2 µL, 296 µmol) was added dropwise at 0 °C and the reaction was left stirring for 3 h. To stop the reaction saturated aqueous NaHCO₃ (20 mL) was added and the mixture was extracted with DCM (2 × 40 mL). The combined organic layers were dried with MgSO₄, concentrated in vacuo and purified through silica gel column chromatography (0→4 % EtOAc/n‐heptane) to afford 2 (55.9 mg, 20 %) as a yellow oil. TLC (EtOAc/n‐heptane, 1:9 v/v): R_f = 0.29. ¹H NMR (400 MHz, CDCl₃) δ 6.28 (d, J = 1.7 Hz, 1H), 6.10 (d, J = 1.6 Hz, 1H), 5.45–5.41 (m, 1H), 4.82 (s, 1H), 3.25–3.15 (m, 1H), 2.71 (td, J = 10.8, 4.6 Hz, 1H), 2.42 (td, J = 7.4, 2.4 Hz, 2H), 2.19–2.10 (m, 1H), 1.91–1.77 (m, 3H), 1.71 (s, 3H), 1.59 (t, J = 7.4 Hz, 2H), 1.38 (s, 3H), 1.11 (s, 3H), 0.92 (t, J = 7.3 Hz, 3H). ¹³C NMR (100 MHz, CDCl₃) δ 154.94, 154.89, 142.58, 134.89, 119.46, 110.72, 110.31, 107.85, 76.83, 45.04, 37.71, 36.17, 31.73, 28.04, 27.71, 24.12, 23.63, 18.64, 14.07. HRMS (m/z): [M + H]⁺ calcd. for C₁₉H₂₆O₂: 287.20110, found 287.20004.
Propyl‐(–)‐trans‐Δ⁸‐tetrahydrocannabinol (13b): Synthesized according to general procedure III from 4′‐bromo‐(–)‐trans‐Δ⁸‐tetrahydrocannabinol (7, 38.2 mg, 118 µmol) and potassium n‐propylboron trifluoride (22, 26.6 mg, 177 µmol) to afford 13b (11.3 mg, 33 %) as a yellow oil. Spectral data were in agreement with previously synthesized 2 and hence no further purification was executed.
3,5‐Dimethoxyiodobenzene (15): 1‐Bromo‐3,5‐dimethoxybenzene (1.09 g, 5.00 mmol) was dissolved in THF (2.5 mL) and kept under protective atmosphere. Magnesium turnings (133 mg, 5.50 mmol) were added and the mixture was stirred vigorously. One drop of 1,2‐dibromoethane (±45 mg, 250 µmol) was added, and a reflux condenser was placed on top of the flask. The reaction was then heated to reflux temperature and allowed to stir for 2 h. After this time, the reaction mixture was cooled on ice, and iodine (845 mg, 3.33 mmol) in THF (2.5 mL) was added. The reaction was allowed to stir for 2 h at 0 °C. After this time, 1M aqueous HCl (10 mL) was added slowly and the mixture was extracted with Et₂O (3 × 10 mL). The combined organic layers were washed with 1M aqueous Na₂S₂O₃ (3 × 10 mL), concentrated in vacuo and purified through silica gel column chromatography (0→10 % EtOAc in n‐heptane) to afford 15 (1.00 g, 76 %) as a brown solidified oil. TLC (EtOAc/n‐heptane, 1:9 v/v): R_f = 0.45. ¹H‐NMR (500 MHz, CDCl₃) δ 6.86 (d, J = 2.2 Hz, 2H), 6.40 (t, J = 2.2 Hz, 1H), 3.76 (s, 6H). ¹³C NMR (100 MHz, CDCl₃) δ 161.07, 115.81, 100.67, 94.05, 55.49. m.p. 72.4 °C.
Chloro(–)‐trans‐Δ⁸‐tetrahydrocannabinol (16 and 17): 5‐Chlorobenzene1,3‐diol (8, 107 mg, 740 µmol) was dissolved in dry DCM (5 mL) and stirred vigorously. (S)‐cis‐verbenol (113 mg, 740 µmol) was added and the reaction was stirred at r.t. Trifluoromethanesulfonic acid (29 µL, 333 µmol) was added dropwise at 0 °C and the reaction was left stirring for 20 h. To stop the reaction saturated aqueous NaHCO₃ (50 mL) was added and the mixture was extracted with DCM (2 × 100 mL). The combined organic layers were dried with MgSO₄, concentrated in vacuo and purified through silica gel column chromatography (0→4 % EtOAc/n‐heptane) to afford 16 (53.3 mg, 26 %) as a yellow oil and 17 as a minor product (13.7 mg, 7 %). 2′‐Chloro(–)‐trans‐Δ⁸‐tetrahydrocannabinol (16): TLC (EtOAc/n‐heptane, 1:5 v/v): R_f = 0.40 ¹H NMR (500 MHz, CDCl₃) δ 6.40 (d, J = 2.6 Hz, 1H), 6.17 (d, J = 2.6 Hz, 1H), 5.39 (s, 1H), 5.36 (d, J = 4.1 Hz, 1H), 3.22 (dd, J = 16.4, 4.4 Hz, 1H), 2.61 (td, J = 10.8, 4.5 Hz, 1H), 2.12–2.02 (m, 1H), 1.77–1.73 (m, 2H), 1.71–1.66 (m, 1H), 1.63 (s, 3H), 1.30 (s, 3H), 0.99 (s, 3H); ¹³C NMR (126 MHz, CDCl₃) δ 155.73, 154.79, 134.68, 134.59, 119.43, 116.99, 110.19, 103.59, 77.39, 45.97, 36.32, 33.57, 28.15, 27.33, 23.44, 18.24; HRMS (m/z): [M + H]⁺ calcd. for C₁₆H₁₉ClO₂: 279.11518, found 279.11664. 4′‐Chloro(–)‐trans‐Δ⁸‐tetrahydrocannabinol (17): TLC (EtOAc/n‐heptane, 1:5 v/v): R_f = 0.47. ¹H NMR (500 MHz, CDCl₃) δ 6.45 (d, J = 2.1 Hz, 1H), 6.29 (d, J = 2.0 Hz, 1H), 5.43 (d, J = 3.7 Hz, 1H), 5.03 (s, 1H), 3.15 (dd, J = 15.7, 4.8 Hz, 1H), 2.67 (td, J = 11.0, 4.8 Hz, 1H), 2.16–2.10 (m, 1H), 1.85–1.76 (m, 3H), 1.70 (s, 3H), 1.37 (s, 3H), 1.09 (s, 3H); ¹³C NMR (126 MHz, CDCl₃) δ 155.72, 155.47, 134.53, 132.14, 119.31, 112.02, 110.79, 107.80, 77.35, 44.68, 35.77, 31.50, 27.80, 27.42, 23.45, 18.45; HRMS (m/z): [M + Na]⁺ calcd. for C₁₆H₁₉O₂Cl: 278.10736, found 278.10653.
Iodo(–)‐trans‐Δ⁸‐tetrahydrocannabinol (18 and 19): 5‐Iodobenzene‐1,3‐diol (9, 110 mg, 466 µmol) was dissolved in dry DCM (5 mL) and stirred vigorously. (S)‐cis‐verbenol (71.0 mg, 466 µmol) was added and the reaction was stirred at r.t. Trifluoromethanesulfonic acid (18.6 µL, 210 µmol) was added dropwise at 0 °C and the reaction was left stirring for 20 h. To stop the reaction saturated aqueous NaHCO₃ (50 mL) was added and the mixture was extracted with DCM (2 × 100 mL). The combined organic layers were dried with MgSO₄, concentrated in vacuo and purified through silica gel column chromatography (0→4 % EtOAc/n‐heptane) to afford 18 (43.7 mg, 25 %) as a yellow oil and 19 as a minor product (11.1 mg, 6 %). 2′‐Iodo(–)‐trans‐Δ⁸‐tetrahydrocannabinol (18): TLC (EtOAc/n‐heptane, 1:1 v/v): R_f = 0.35. ¹H NMR (500 MHz, CDCl₃) δ 7.00 (d, J = 2.6 Hz, 1H), 6.31 (d, J = 2.6 Hz, 1H), 5.44 (d, J = 3.7 Hz, 1H), 5.25 (s, 1H), 3.48 (dd, J = 17.2, 3.6 Hz, 1H), 2.52 (td, J = 10.7, 4.3 Hz, 1H), 2.19–2.13 (m, 1H), 1.93–1.82 (m, 2H), 1.72 (s, 3H), 1.69–1.66 (m, 1H), 1.36 (s, 3H), 1.05 (s, 3H); ¹³C NMR (126 MHz, CDCl₃) δ 155.09, 154.57, 134.64, 121.41, 120.46, 119.70, 105.30, 96.81, 77.28, 46.96, 37.45, 37.19, 28.40, 27.22, 23.41, 18.09. HRMS (m/z): [M + H]⁺ calcd. for C₁₆H₁₉IO₂: 371.05080, found 371.05235. 4′‐Iodo(–)‐trans‐Δ⁸‐tetrahydrocannabinol (19): TLC (EtOAc/n‐heptane, 1:1 v/v): R_f = 0.44. ¹H NMR (500 MHz, CDCl₃) δ 6.80 (d, J = 1.7 Hz, 1H), 6.62 (d, J = 1.7 Hz, 1H), 5.42 (d, J = 4.0 Hz, 1H), 4.93 (s, 1H), 3.15 (dd, J = 15.3, 4.4 Hz, 1H), 2.66 (td, J = 11.0, 4.7 Hz, 1H), 2.16–2.10 (m, 1H), 1.83–1.73 (m, 3H), 1.69 (s, 3H), 1.36 (s, 3H), 1.08 (s, 3H); ¹³C NMR (126 MHz, CDCl₃) δ 155.80, 155.53, 134.53, 119.80, 119.30, 116.35, 113.37, 90.32, 77.31, 44.65, 35.66, 31.61, 27.80, 27.43, 23.45, 18.47; HRMS (m/z): [M + Na]⁺ calcd. for C₁₆H₁₉O₂I: 370.04297, found 370.04265.
n‐Propylboronic acid (20): 1‐Bromopropane (2.15 mL, 23.6 mmol) and dry THF (12 mL) were combined and cooled to 0 °C. Magnesium turnings (631 mg, 25.9 mmol) and one drop of 1,2‐dibromoethane were added. After 15 min the cooling bath was removed and the reaction was refluxed for 2 h at 75 °C after which it was cooled to r.t. Trimethylborate (2.89 mL, 25.9 mmol) was dissolved in Et₂O (100 mL), stirred vigorously and cooled to –78 °C. Freshly prepared propylmagnesium bromide was added dropwise to the mixture. The reaction was left stirring for 2 h at –78 °C after it was warmed up to r.t. 10 % aqueous HCl (80 mL) was added slowly and the biphasic reaction mixture was left stirring for 15 min. The layers were separated and the aqueous layer was washed with Et₂O (2 × 80 mL). The combined organic layers were dried with MgSO₄, concentrated in vacuo and the crude product was recrystallized by dissolving in hot water (20 mL) and cooling to 0 °C. The product was isolated by filtration and the flask and filter were rinsed with n‐heptane (4 mL). The filtered solid was dried under high vacuum to afford 20 (539 mg, 26 % over two steps) as white crystals. ¹H NMR (400 MHz, (CD₃)₂SO) δ 7.33 (s, 2H), 1.39–1.28 (m, 3H), 0.85 (t, J = 7.3 Hz, 2H), 0.57 (t, J = 7.7 Hz, 3H). ¹³C NMR (100 MHz, CDCl₃) δ 17.54, 17.09 (CH₂ next to B not visible; quadrupolar relaxation). ¹¹B NMR (128 MHz, CDCl₃) δ 32.18 (s). m.p. 101.1 °C.
n‐Pentylboronic acid (21): Trimethylborate (1.1 mL, 10.0 mmol) was dissolved in Et₂O (60 mL), stirred vigorously and cooled to –78 °C. Pentylmagnesium bromide (7.69 mL, 10.0 mmol, 1.3M in THF) was added dropwise. The reaction was left stirring for 2 h at –78 °C after it was warmed up to r.t. 10 % aqueous HCl (40 mL) was added slowly and the biphasic reaction mixture was left stirring for 15 min. The layers were separated and the aqueous layer was washed with Et₂O (2 × 40 mL). The combined organic layers were dried with MgSO₄, concentrated in vacuo and the crude product was recrystallized by dissolving in hot water (10 mL) and cooling to 0 °C. The product was isolated by filtration and the flask and filter were rinsed with n‐heptane (2 mL). The filtered solid was dried under high vacuum to afford 21 (774 mg, 67 %) as white crystals. ¹H NMR (400 MHz, CDCl₃) δ 1.49–1.36 (m, 2H), 1.34–1.27 (m, 4H), 0.95–0.84 (m, 4H), 0.84–0.75 (m, 1H). ¹³C NMR (100 MHz, CDCl₃) δ 34.68, 28.20, 23.47, 22.65, 14.15. ¹¹B NMR (128 MHz, CDCl₃) δ 33.32 (s). m.p. 88.2 °C.
Potassium n‐propylboron trifluoride (22): Synthesized according to general procedure I from n‐propylboronic acid (20, 200 mg, 2.28 mmol), potassium fluoride (529 mg, 9.10 mmol) and 2,3‐dihydroxysuccinic acid (700 mg, 4.66 mmol) to afford 22 (257 mg, 75 %) as white crystals. ¹H NMR (400 MHz, (CD₃)₂SO) δ 1.22–1.06 (m, 2H), 0.83–0.76 (m, 3H), –0.01 to –0.10 (m, 2H). ¹³C NMR (100 MHz, (CD₃)₂SO) δ 18.74, 18.23 (CH₂ next to B not visible; quadrupolar relaxation). ¹¹B NMR (128 MHz, (CD₃)₂SO) δ 4.76 (d, J = 64.8 Hz). ¹⁹F NMR (377 MHz (CD₃)₂SO) δ –136.49 to –136.98 (m). m.p. 378.9 °C.
Potassium n‐pentylboron trifluoride (23): Synthesized according to general procedure I from n‐pentylboronic acid (21, 600 mg, 5.17 mmol), potassium fluoride (1.20 g, 20.7 mmol) and 2,3‐dihydroxysuccinic acid (1.59 g, 10.6 mmol) to afford 23 (872 mg, 95 %) as white crystals. ¹H NMR (400 MHz, (CD₃)₂SO) δ 1.26–1.07 (m, 6H), 0.82 (t, J = 7.1 Hz, 3H), –0.03 to –0.14 (m, 2H). ¹³C NMR (100 MHz, (CD₃)₂SO) δ 35.54, 25.30, 22.44, 14.18 (CH₃) (CH₂ next to B not visible; quadrupolar relaxation). ¹¹B NMR (128 MHz, (CD₃)₂SO) δ 4.83 (d, J = 65.6 Hz). ¹⁹F NMR (377 MHz (CD₃)₂SO) δ –136.86 (d, J = 74.4 Hz). m.p. 392.2 °C.
Potassium (1‐naphthalene) trifluoroborate (24): Synthesized according to general procedure I from naphthalene‐1‐ylboronic acid (400 mg, 2.33 mmol), potassium fluoride (540 mg, 9.30 mmol) and 2,3‐dihydroxysuccinic acid (716 mg, 4.77 mmol) to afford 24 (525 mg, 97 %) as white crystals. ¹H NMR (400 MHz, (CD₃)₂SO) δ 8.39 (d, J = 8.8 Hz, 1H), 7.74–7.69 (m, 1H), 7.57 (d, J = 8.2 Hz, 1H), 7.55–7.52 (m, 1H), 7.34–7.23 (m, 3H). ¹³C NMR (100 MHz, (CD₃)₂SO) δ 136.63, 132.99, 130.29, 128.55, 127.38, 125.20, 124.93, 123.90, 123.38 (C next to B not visible; quadrupolar relaxation). ¹¹B NMR (128 MHz, (CD₃)₂SO) δ 3.51 (d, J = 56.0 Hz). ¹⁹F NMR (377 MHz (CD₃)₂SO) δ –135.27 (d, J = 65.0 Hz). m.p. 117.9 °C.
Potassium (4‐methoxyphenyl) trifluoroborate (25): Synthesized according to general procedure I from (4‐methoxyphenyl)boronic acid (400 mg, 2.63 mmol), potassium fluoride (612 mg, 10.5 mmol) and 2,3‐dihydroxysuccinic acid (810 mg, 5.40 mmol) to afford 25 (548 mg, 97 %) as white crystals. ¹H NMR (400 MHz, (CD₃)₂SO) δ 7.21 (d, J = 8.4 Hz, 2H), 6.66 (d, J = 7.7 Hz, 2H), 3.66 (s, 3H, CH₃). ¹³C NMR (100 MHz, (CD₃)₂SO) δ 157.20, 132.25, 111.87, 54.55 (C next to B not visible; quadrupolar relaxation). ¹¹B NMR (128 MHz, (CD₃)₂SO) δ 3.44 (m). ¹⁹F NMR (377 MHz (CD₃)₂SO) δ –138.19 (m). m.p. 256.9 °C.