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

Muhammad Nawaz; Muhammad Farooq Ibad; Obaid-Ur-Rahman Abid; Rasheed Ahmad Khera; Alexander Villinger; Peter Langer

doi:10.1055/s-0029-1218522

LETTER

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

Muhammad Nawaz^a, Muhammad Farooq Ibad^a, Obaid-Ur-Rahman Abid^a, Rasheed Ahmad Khera^a, Alexander Villinger^a, 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

Abstract

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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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References and Notes

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<A NAME="RD24509ST-8">8</A> For a review of cross-coupling reactions of polyhalogenated heterocycles, see: Schröter S. Stock C. Bach T. Tetrahedron 2005, 61: 2245

For palladium-catalyzed reactions from our group, see:

<A NAME="RD24509ST-9A">9a</A> Dang TT. Dang TT. Ahmad R. Reinke H. Langer P. Tetrahedron Lett. 2008, 49: 1698

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<A NAME="RD24509ST-9D">9d</A> Dang TT. Dang TT. Rasool N. Villinger A. Langer P. Adv. Synth. Catal. 2009, 351: 1595

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For reactions with organozinc compounds, see:

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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.

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.

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.

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.

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.