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Synlett 2009(13): 2154-2156  
DOI: 10.1055/s-0029-1217544
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

Synthesis of Functionalized 2′,4-Diarylbenzophenones Based on Site-Selective Suzuki Cross-Coupling Reactions

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

Received 6 April 2009
Publication Date:
10 July 2009 (online)

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Abstract

The palladium(0)-catalyzed Suzuki cross-coupling reaction of the bis(triflates) of 2′,4-dihydroxybenzophenones afforded 2′,4-diarylbenzophenones. The reactions proceeded with very good site selectivity. The first attack occurred at carbon atom C-4.

Key Words

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

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Typical Procedure for the Synthesis of 6a-j:
A 1,4-dioxane solution (5 mL/mmol of 4) of 5a-j, K3PO4, Pd(PPh3)4 and 4 was stirred at 110 ˚C for 4 h. 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 4′-Methyl-4-(4′-methylbiphenylcarbonyl)-biphenyl-2-carboxylate (6a): Starting with 4 (220 mg, 0.4 mmol), K3PO4 (261 mg, 1.2 mmol), Pd(PPh3)4 (3 mol%), p-tolylboronic acid (144 mg, 1.1 mmol) and 1,4-dioxane (2 mL), 6a was isolated as a highly viscous oil (200 mg, 84%). ¹H NMR (300 MHz, CDCl3): δ = 2.17 (s, 3 H, CH3), 2.30 (s, 3 H, CH3), 3.56 (s, 3 H, OCH3), 6.95 (d, 2 H, J = 8.0 Hz, ArH), 7.04-7.21 (m, 6 H, ArH), 7.35-7.53 (m, 5 H, ArH), 7.70 (dd, 1 H, J = 1.9, 8.0 Hz, ArH), 7.98 (d, 1 H, J = 1.9 Hz, ArH). ¹³C NMR (62.89 MHz, CDCl3): δ = 21.0 (CH3), 21.2 (CH3), 52.1 (OCH3), 126.9 (4 × C, CH), 127.9, 128.8, 128.9 (CH), 129.0 (4 × C, CH), 130.2, 130.6, 131.4, 132.1 (CH), 135.8 (2 × C), 137.1 (C), 137.2 (2 × C), 137.7, 138.3, 141.3, 146.3, 168.4 (C), 197.4 (C=O). IR (KBr): 3080, 3057, 3025 (w), 1724, 1659 (s), 1613 (w), 1595 (m), 1574, 1518 (w), 1438, 1310, 1277 (m), 1231 (s), 1152, 1082, 972 (m), 819, 704 (s), 536 (m) cm-¹. GC-MS (EI, 70 eV): m/z (%) = 420 (100) [M+], 405 (21), 373 (09), 359 (23), 332 (07), 253 (26), 210 (07), 195 (40), 165 (39), 152 (25). HRMS (EI): m/z [M+] calcd for C29H24O3: 420.17200; found: 420.17153.

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Methyl 2′-Bromo-4-[2-(trifluoromethylsulfonyloxy)-benzoyl]biphenyl-2-carboxylate (7d): Starting with 4 (150 mg, 0.3 mmol), K3PO4 (171 mg, 0.8 mmol), Pd(PPh3)4 (3 mol%), 2-bromophenylboronic acid (65 mg, 0.3 mmol) and 1,4-dioxane (2 mL), 7d was isolated as a highly viscous oil (120 mg, 78%). ¹H NMR (300 MHz, CDCl3): δ = 3.58 (s, 3 H, OCH3), 7.13-7.17 (m, 2 H, ArH), 7.28-7.39 (m, 3 H, ArH), 7.43-7.48 (m, 1 H, ArH), 7.54-7.62 (m, 3 H, ArH), 7.94 (dd, 1 H, J = 2.1, 8.0 Hz, ArH), 8.36 (d, 1 H, J = 2.1 Hz, ArH). ¹³C NMR (75.46 MHz, CDCl3): δ = 52.3 (OCH3), 122.7, 127.1, 128.3, 129.2, 129.7, 129.8, 131.3, 131.8, 132.3, 132.9, 133.2 (CH), 134.6, 134.9, 135.0, 136.0, 141.5, 146.7, 146.8, 147.2, 166.2 (C), 191.4 (C=O). ¹9F NMR (282 MHz, CDCl3): δ = -73.29 (CF). IR (KBr): 3053, 2953, 2923 (w), 1728, 1672 (s), 1567 (m), 1482 (w), 1309, 1294 (m), 1241, 1203 (s), 1168 (m), 1087 (s), 948 (m), 887, 769, 592 (s) cm-¹. MS (EI, 70 eV): m/z (%) = 544 (100) [M+], 331 (12), 301 (48), 271 (24), 242 (75), 215 (7), 183 (5), 151 (11), 69 (15). HRMS (EI): m/z [M+] calcd for C22H14BrF3O6S: 544.17200; found: 544.171525.