Journal of the Korean Chemical Society (대한화학회지)

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Copper(II) Triflate-Induced Oxidative Coupling of Grignard Reagents

Copper(II) Triflate로 유도된 Grignard 시약의 산화성 짝지음

  • Lee, Jae-In (Department of Chemistry, Duksung Women's University)
  • 이재인 (덕성여자대학교 자연과학대학 화학과)
  • Published : 2005.02.20
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Abstract

Keywords

EXPERIMENTAL

Preparation of 4,4'-dimethoxybiphenyl (typical procedure). To a stirred solution of copper(II) triflate (868.0 mg, 2.4 mmol) in tetrahydrofuran (15 mL) precooled to -78 ℃ was slowly added p-methoxyphenylmagnesium bromide (8.0 mL, 0.3 M in THF, 2.4 mmol) under argon. The resulting brownish yellow solution was allowed to warm to 0 ℃ over 1 h and then 4 mL of 10% NH4OH/sat. NH4Cl was added to the reaction mixture. After evaporation of THF, the reaction mixture was extracted with methylene chloride (3×20 mL) and washed with 10% NH4OH/sat. NH4Cl (30 mL). The combined organic phases were dried over anhydrous MgSO4, filtered, and evaporated to dryness in vacuo. The crude product was purified by short pathway silica gel column chromatography using 20% EtOAc/n-hexane as an eluant to afford 4,4'-dimethoxybiphenyl (244.3 mg, 95%). M.p. 174-175 ℃(lit.10 175-176 ℃); 1H NMR (300 MHz, CDCl3) δ 7.47 (d, J=9.0 Hz, 4H), 6.95 (d, J=9.0 Hz, 4H), 3.84 (s, 6H); FT-IR (KBr) 3056, 2957, 1608, 1510, 1455, 1251, 1041, 824 cm−1; Ms m/z(%) 214(M+, 100), 199(92), 171(34), 128(18). Spectral data, Hexadecane: B.p. 105-110 ℃/0.8 mm Hg(lit.13 149 ℃/10 mm Hg); 1H NMR (300 MHz, CDCl3) δ 0.88 (t, J=6.0 Hz, 6H), 1.22-1.30 (m, 28H); FT-IR (film) 2923, 2854, 1466, 1378, 721 cm−1; Ms m/z(%) 226(M+, 9), 113(10), 99(20), 85(63), 71(81), 57(100). 1,2-Diphenylethane: M.p. 51-52 ℃(lit.13 52.2 ℃); 1H NMR (300 MHz, CDCl3) δ 7.25-7.30 (m, 4H), 7.16-7.21 (m, 6H), 2.92 (s, 4H); FT-IR (KBr) 3059, 3026, 2942, 2856, 1601, 1493, 1452, 1064, 752, 698 cm−1; Ms m/z(%) 182(M+, 48), 92(10), 91(100), 65(16). Bicyclohexyl: B.p. 68-73 ℃/0.6 mm Hg(lit.13 238 ℃/760 mm Hg); 1H NMR (300 MHz, CDCl3) δ 1.57-1.72 (m, 10H), 0.88-1.24 (m, 12H); FT-IR (film) 2922, 2861, 1448, 895 cm−1; Ms m/z(%) 166(M+, 41), 83(47), 82(100), 67(49), 55(42). 1,4-Diphenyl-1,3-butadiyne: M.p. 83-85 ℃; 1H NMR (300 MHz, CDCl3) δ 7.52-7.55 (m, 4H), 7.29-7.38 (m, 6H); FT-IR (KBr) 3049, 2150, 1593, 1485, 916, 756, 687 cm−1; Ms m/z(%) 202(M+, 100), 201(17), 200(33), 150(9), 101(8). Biphenyl: M.p. 69-70 ℃(lit.10 69-70 ℃); 1H NMR (300 MHz, CDCl3) δ 7.50-7.54 (m, 4H), 7.33-7.39 (m, 4H), 7.24-7.30 (m, 2H); FT-IR (KBr) 3034, 1597, 1481, 1429, 1091, 729, 697 cm−1; Ms m/z(%) 154(M+, 100), 153(47), 152(33), 76(11). 2,2'-Dimethylbiphenyl: B.p. 85-90 ℃/0.8 mm Hg (lit.13 256 ℃/760 mm Hg); 1H NMR (300 MHz, CDCl3) δ 7.25-7.32 (m, 6H), 7.16 (d, J=6.3 Hz, 2H), 2.11 (s, 6H); FT-IR (film) 3060, 3017, 2922, 1600, 1478, 1453, 1379, 1008, 754 cm−1; Ms m/z(%) 182(M+, 68), 167(100), 166(23), 165(48), 152(22). 4,4'-Dimethylbiphenyl: M.p. 120-121 ℃(lit.9 119-121 ℃); 1H NMR (300 MHz, CDCl3) δ 7.51-7.54 (m, 4H), 7.27-7.29 (m, 4H), 2.44 (s, 6H); FT-IR (KBr) 3025, 2919, 1501, 1449, 1265, 804 cm−1; Ms m/z(%) 182(M+, 100), 181(31), 167(52), 166(17), 165(39), 152(15). 4,4'-Dichlorobiphenyl: M.p. 145- 147 ℃(lit.9 146-148 ℃); 1H NMR (300 MHz, CDCl3) δ 7.40 (d, J=8.7 Hz, 4H), 7.33 (d, J=8.7 Hz, 4H); FT-IR (KBr) 3051, 1647, 1388, 1090, 814 cm−1; Ms m/z(%) 226(M++4, 11), 224(M++2, 65), 222(M+, 100), 152(56), 151(16), 111(9). 2,2',4,4',6,6'-Hexamethylbiphenyl: M.p. 96-97 ℃; 1H NMR (300 MHz, CDCl3) δ 6.93 (s, 4H), 2.32 (s, 6H), 1.86 (s, 12H); FT-IR (KBr) 3025, 2915, 1609, 1471, 1375, 1003, 852 cm−1; Ms m/z(%) 238(M+, 79), 224(20), 223(100), 208(46), 193(33), 178(11). 1,1'-Binaphthyl: M.p. 158-160 ℃(lit.10 158-160 ℃); 1H NMR (300 MHz, CDCl3) δ 7.90-7.97 (m, 4H), 7.53-7.60 (m, 2H), 7.40-7.51 (m, 4H), 7.35-7.40 (m, 2H), 7.20-7.29 (m, 2H); FT-IR (KBr) 3049, 1589, 1504, 1383, 802, 778 cm−1; Ms m/z(%) 254(M+, 89), 253(100), 252(84), 239(27), 126(31). 2,2'-Bithiophene: B.p. 87-92 ℃/0.9 mm Hg(lit.13 103 ℃/3.0 mm Hg); 1H NMR (300 MHz, CDCl3) δ 7.14-7.19 (m, 4H), 6.98 (dd, J1=5.0 Hz, J2=3.7 Hz, 2H); FT-IR (film) 3075, 1500, 1415, 1049, 827, 816 cm−1; Ms m/z(%) 167(M++1, 12), 166(M+, 100), 165(10), 134(15), 121(27).

 

RESULTS AND DISCUSSION

To investigate the relative effectiveness of copper (II) salts for the oxidative coupling of Grignard reagents we added p-methylphenylmagnesium bromide to a solution of copper(II) bromide, copper(II) chloride, and copper(II) nitrate in THF at -78 ℃. 4,4'-Dimethylbiphenyl was obtained in 67%, 47%, and 32% yield, respectively, after 1 h between -78 ℃ and 0 ℃. However, the reaction of copper(II) triflate with p-methylphenylmagnesium bromide in THF proceeded well to give 4,4'-dimethylbiphenyl in 81% yield after 1 h between -78 ℃ and 0 ℃ (Scheme 1). The addition of Grignard reagents to a solution of copper(II) triflate in THF at -78 ℃ resulted in color changes starting with brownish yellow and proceeding through deep brown at 0 ℃. Aqueous work-up with 10% NH4OH/ sat. NH4Cl and purification by short pathway silica gel column chromatography or vacuum distillation with a Kugelrohr apparatus gave only the symmetrical coupling products without side products.

Scheme 1

Table 1.Preparation of bialkyls and biaryls from Grignard reagents and copper(II) triflate

The catalytic effect of copper(II) triflate for the oxidative coupling of p-methylphenylmagnesium bromide was also briefly studied. The addition of p-methylphenylmagnesium bromide to a THF solution of 0.5 equiv and 0.75 equiv of copper(II) triflate afforded 4,4'-dimethylbiphenyl in 60% and 71% yield, respectively, after 1 h between -78 ℃ and 0 ℃. Thus, copper(II) triflate did not nearly play a catalytic effect and, therefore, 1 equiv of copper(II) triflate was requisite for the high yield formation of the dimeric products.

Table 1 summarized the results of the oxidative coupling reaction of alkyl, alkynyl, and aryl Grignard reagents with an equimolar amount of copper (II) triflate in THF. The reaction worked well both for aliphatic and aromatic Grignard reagents and thus it showed somewhat wider applicability than the reported methods. The treatment of copper(II) triflate with primary and secondary alkyl Grignard reagents (entry 1-3) afforded the corresponding bialkyls in high yields (73-94%). Furthermore, the reaction of phenylethynylmagnesium bromide (entry 4) with copper(II) triflate proceeded smoothly to give 1,4-diphenyl-1,3-butadiyne in 70% yield. Similarly, aryl Grignard reagents (entry 5-12) gave the coupled biaryls in high yields (75-95%). The reaction of aryl Grignard reagents having electron donating group (entry 7, 8) in 4-position gave somewhat higher yield than that of aryl Grignard reagent having electron withdrawing group (entry 9) in 4-position. This reaction was also applicable to the coupling of 2-methylphenylmagnesium chloride (entry 6) and 2,4,6-trimethylphenylmagnesium bromide (entry 10) with copper(II) triflate, producing the corresponding biaryls in 77% and 79% yield, respectively. The presence of o-methyl substituent in aryl Grignard reagents did not affect the efficiency of the oxidative coupling with copper(II) triflate under the present reaction conditions.

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