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Synlett 2010(1): 150-152  
DOI: 10.1055/s-0029-1218522
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

Synthesis of Functionalized p-Terphenyls Based on Site-Selective Suzuki Cross-Coupling Reactions of Bis(triflates) of 2,5-Dihydroxybenzoate

Muhammad Nawaza, Muhammad Farooq Ibada, Obaid-Ur-Rahman Abida, Rasheed Ahmad Kheraa, Alexander Villingera, Peter Langer*a,b
a Institut für Chemie, Universität Rostock, Albert Einstein Str. 3a, 18059 Rostock, Germany
Fax: +49(381)4986412; e-Mail: peter.langer@uni-rostock.de;
b Leibniz-Institut für Katalyse an der Universität Rostock e.V., Albert Einstein Str. 29a, 18059 Rostock, Germany
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Publication History

Received 2 September 2009
Publication Date:
18 November 2009 (online)

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Synthesis of Functionalized p-Terphenyls Based on Site-Selective Suzuki Cross-Coupling Reactions of Bis(triflates) of 2,5-DihydroxybenzoateSynlett 2010; 2010(01): e1-e1
DOI: 10.1055/s-0029-1219148

Abstract

The palladium(0)-catalyzed Suzuki cross-coupling reaction of the bis(triflates) of methyl 2,5-dihydroxybenzoate afforded p-terphenyls. The reactions proceeded with very good site selectivity. The first attack occurred at carbon atom C-5.

Key words

terphenyls - cross-coupling - palladium - site-selectivity - Suzuki reaction

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Synthesis of Methyl 2,5-Bis(trifluoromethylsulfonyloxy)-benzoate (2)
To a solution of 1 (1.0 equiv) in CH2Cl2 (10 mL/1 mmol of 1), was added pyridine (4.0 equiv) at -78 ˚C under an argon atmosphere. After stirring for 10 min, Tf2O (2.4 equiv) was added at -78 ˚C. The mixture was allowed to warm to 0 ˚C and stirred for 4 h. The reaction mixture was filtered, and the filtrate was concentrated in vacuo. The products of the reaction mixture were isolated by rapid column chromatog-raphy (flash silica gel, heptanes-EtOAc). Starting with 1 (168 mg, 1.0 mmol), pyridine (0.32 mL, 4.0 mmol) and Tf2O (0.39 mL, 2.4 mmol), 2 was isolated as highly viscous oil (350 mg, 81%). ¹H NMR (300 MHz, CDCl3): δ = 3.92 (s, 3 H, OCH3), 7.36 (s, 1 H, ArH), 7.47 (d, 1 H, J = 6.2 Hz, ArH), 7.92 (d, 1 H, J = 6.1 Hz, ArH). ¹³C NMR (75.46 MHz, CDCl3): δ = 53.2 (OCH3), 116.5 (q, J F,C = 320.0 Hz, CF3), 119.0 (q, J F,C = 321.1 Hz, CF3), 125.0, 125.6, 127.0 (CH), 134.2, 147.1, 147.9 (C), 162.3 (C=O). ¹9F NMR (282 MHz, CDCl3): δ = -73.3 (CF). IR (KBr): ν = 3121, 3088, 2961 (w), 1736, 1618 (s), 1586 (m), 1485, 1300, 1279 (m), 1244 (s), 1124, 1075, 977 (m), 875, 781, 759 (s), 698, 581, 543 (m) cm-¹. GC-MS (EI, 70 eV): m/z (%) = 432 (70) [M+], 401 (40), 363 (06), 337 (02), 299 (32), 273 (13), 235 (98), 205 (27), 179 (24), 135 (62), 107 (33), 79 (26), 69 (100), 53 (28). HRMS (EI): m/z calcd for C10H6F6O8S2 [M+]: 431.94028; found: 431.940891.

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General Procedure for Suzuki Reactions
A 1,4-dioxane solution of the arylboronic acid, K3PO4, Pd(PPh3)4, and 2 or 5a-g was stirred at 110 ˚C for 4 h under argon atmosphere. After cooling to 20 ˚C, a sat. aq solution of NH4Cl was added. The organic and the aqueous layer were separated, and the latter was extracted with CH2Cl2. The combined organic layers were dried (Na2SO4), filtered, and the filtrate was concentrated in vacuo. The residue was purified by column chromatography.

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Methyl 2,5-Bis(4- tert -butylphenyl)benzoate (4b)
Starting with 2 (216 mg, 0.5 mmol), K3PO4 (292 mg, 1.4 mmol), Pd(PPh3)4 (6 mol%), 4-tert-butylphenylboronic acid (211 mg, 1.2 mmol), and 1,4-dioxane (5 mL per 1 mmol of 2), 4b was isolated as a highly viscous oil (150 mg, 75%). ¹H NMR (300 MHz, CDCl3): δ = 1.28 (s, 18 H, 6 CH3), 3.58 (s, 3 H, OCH3), 7.15-7.42 (m, 8 H, ArH), 7.49 (s, 1 H, ArH), 7.63 (d, 1 H, J = 5.0 Hz, ArH), 7.94 (d, 1 H, J = 6.9 Hz, ArH). ¹³C NMR (75.46 MHz, CDCl3): δ = 31.3 (3 CH3), 31.4 (3 CH3), 34.5, 34.6 (C), 51.9 (OCH3), 125.0, 125.8, 126.7, 128.0, 128.2, 129.5, 131.2 (CH), 131.3, 136.8, 137.8, 139.7, 140.8, 150.1, 150.8 (C), 169.4 (C=O). IR (KBr): ν = 3031, 2951, 2902 (w), 1727 (s), 1605 (w), 1483 (m), 1461, 1362, 1267 (m), 1234 (s), 1180, 1085, 959, 895, 788, 765, 698, 572, 554 (m) cm-¹. GC-MS (EI, 70 eV): m/z (%) = 400(58) [M+], 385 (100), 357 (02), 297 (03), 252 (02), 185 (14), 157 (09), 141 (04), 57 (06), 41 (03). HRMS (EI): m/z calcd for C28H32O2 [M+]: 400.23968; found: 400.239581.

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CCDC-749223 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.

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Methyl 5-(3,5-Dimethylphenyl)-2-(trifluoromethyl-sulfonyloxy)benzoate (5a)
Starting with 2 (216 mg, 0.5 mmol), K3PO4 (146 mg, 0.7 mmol), Pd(PPh3)4 (3 mol%), 3,5-dimethylphenylboronic acid (89 mg, 0.65 mmol), and 1,4-dioxane (5 mL/1 mmol of 2), 5a was isolated as a highly viscous oil (161 mg, 83%). ¹H NMR (300 MHz, CDCl3): δ = 2.27 (s, 6 H, 2 CH3), 3.61 (s, 3 H, OCH3), 6.82 (s, 2 H, ArH), 6.95 (s, 1 H, ArH), 7.35 (d, 1 H, J = 6.1 Hz, ArH), 7.36 (s, 1 H, ArH), 7.62 (d, 1 H, J = 2.3 Hz, ArH). ¹³C NMR (62.89 MHz, CDCl3): δ = 21.2 (2 CH3), 52.3 (OCH3), 116 (q, J F,C = 318.0 Hz, CF3), 122.4, 123.7, 126.0, 129.6, 132.6 (CH), 137.7, 139.2, 141.1, 143.0, 148.0 (C), 167.1 (C=O). ¹9F NMR (282 MHz, CDCl3): δ =
-73.4 (CF). IR (KBr): ν = 3018, 2951, 2920 (w), 1723, 1601 (s), 1489 (m), 1467, 1328, 1271 (m), 1243 (s), 1137, 1099, 978 (m), 863, 785, 751 (s), 699, 577, 540 (m) cm-¹. GC-MS (EI, 70 eV): m/z (%) = 388 (M+, 66), 357 (07), 255 (100), 227 (12), 152 (15), 115 (03), 69 (08). HRMS (EI): m/z calcd for C17H15F3O5S [M+]: 388.05868; found: 388.058797.