Iron-Catalyzed Cross-Coupling between Alkenyl and Dienyl Sulfonates and Functionalized Arylcopper Reagents

Abstract

Functionalized arylcopper reagents react readily with alkenyl sulfonates in the presence of catalytic amounts of Fe(acac)₃ (10 mol%) providing the expected cross-coupling products in good yields. Ester or cyano group are tolerated. This cross-coupling can be performed with dienyl sulfonates leading to the corresponding substituted dienes.

Key words

catalysis - cross-coupling - organomagnesium reagents - triflates - nonaflates

References

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• 5a

  Alkenyl sulfonates 1a and 1b were prepared by treating the corresponding aldehyde with 1.4 equiv of t-BuOK in refluxing THF for 4 h and quenching of the resulting enolate with N-phenyl-bis(trifluoromethanesulfonimide) and nonafluorobutanesulfonyl fluoride (NfF), respectively. Compounds 1c and 1f were prepared following a literature procedure, see ref. 5b. Nonaflate 1d was obtained from the corresponding ketone via treatment with LDA and NfF. Dienyl nonaflate 1g was prepared from the corresponding commercially available trimethylsilyl enol ether upon treatment with MeLi, followed by NfF.

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7

Typical Procedure - Preparation of Ethyl 4-(2,2-Di-phenylvinyl)benzoate ( 4b).
A 25 mL flame-dried Schlenk tube flushed with argon was charged with ethyl 4-iodobenzoate (2.9 mmol, 773 mg), DME (5 mL) and cooled to -20 °C. Isopropylmagnesium chloride (2.9 mmol, 1.33 mL of a 2.1 M solution in THF) was then slowly added and the reaction mixture was stirred at -20 °C until GC analysis of reaction aliquots indicated complete exchange. Subsequently, a solution of CuCN·2LiCl (2.8 mmol, 2.8 mL of a 1 M solution in THF) was added and the reaction mixture was stirred for 20 min. A solution of (2,2-diphenylvinyl)trifluoromethanesulfonate (330 mg, 1 mmol) and Fe(acac)₃ (38 mg, 0.1 mmol) in DME (3 mL) was added at once at -20 °C and the reaction mixture was stirred at r.t. for 1 h. The reaction was quenched with sat. NH₄Cl (aq), and extracted several times with Et₂O. The combined organic phases were washed with a 2:1 mixture of NH₃ (aq) and NH₄Cl (aq), sat. brine, dried over MgSO₄ and concentrated under reduced pressure. Purification via column chromatography (elution with a 99:1 pentane-Et₂O mixture) afforded the stilbene (4b) as a yellow oil (254 mg, 77%). ¹H NMR (300 MHz, CDCl₃): δ = 7.72 (unresolved d, J = 8.4 Hz, 2 H), 7.21-7.28 (m, 8 H), 7.08-7.13 (m, 2 H), 6.99 (unresolved d, J = 8.6 Hz, 2 H), 6.91 (s, 1 H), 4.25 (q, J = 7.1 Hz, 2 H), 1.27 (t, J = 7.1 Hz, 3 H). ¹³C NMR (75 MHz, CDCl₃): δ = 166.8, 145.3, 143.3, 142.4, 140.2, 130.7, 129.7, 129.6, 129.1, 128.7, 128.7, 128.3, 128.1, 128.1, 127.5, 61.2, 14.7. HRMS: m/z calcd: 328.1463; found: 328.1455. MS (EI, 70 eV): m/z (%) = 328 (100), 283 (18), 255 (48), 239 (14).
1-[2-(4-Methoxyphenyl)-1-phenylvinyl]benzene ( 4c): ¹H NMR (300 MHz, CDCl₃): δ = 7.21-7.29 (m, 7 H), 7.18-7.20 (m, 1 H), 7.12-7.16 (m, 2 H), 6.88 (unresolved d, J = 8.6 Hz, 2 H), 6.84 (s, 1 H), 6.59 (unresolved d, J = 8.8 Hz, 2 H), 3.67 (s, 3 H). ¹³C NMR (75 MHz, CDCl₃): δ = 158.8, 144.0, 141.0, 141.0, 131.2, 130.8, 130.5, 129.1, 128.5, 128.0, 127.8, 127.7, 127.6, 113.8, 55.5. HRMS: m/z calcd: 286.1358; found: 286.1341. MS (EI, 70 eV): m/z (%) = 286 (100), 165 (15).
1-{(2-[3-(Trifluoromethyl)phenyl]-1-phenyl-vinyl}benzene ( 4d): ¹H NMR (300 MHz, CDCl₃): δ = 7.21-730 (m, 9 H), 7.16-7.19 (m, 2 H), 7.08-7.13 (m, 3 H), 6.90 (s, 1 H). ¹³C NMR (75 MHz, CDCl₃): δ = 145.0, 143.1, 140.0, 138.5, 132.9, 130.5, 129.2, 128.7, 128.3, 128.2, 128.0, 126.8, 126.7, 126.6, 123.6, 123.3. HRMS: m/z calcd: 324.1126; found: 324.1118. MS (EI, 70 eV): m/z (%) = 324 (100), 283 (10), 255 (13), 178 (11).
3-(2,2-Diphenylvinyl)benzonitrile ( 4f): ¹H NMR (300 MHz, CDCl₃): δ = 7.22-7.32 (m, 9 H), 7.19-7.21 (m, 1 H), 7.11-7.16 (m, 2 H), 7.05-7.11 (m, 2 H), 6.83 (s, 1 H). ¹³C (75 MHz, CDCl₃): δ = 145.8, 142.9, 139.7, 139.1, 134.0, 133.3, 132.6, 130.5, 130.4, 129.5, 129.3, 129.1, 128.7, 128.6, 128.5, 128.1, 125.9, 112.6. HRMS: m/z calcd: 281.1204; found: 281.1186. IR (KBr): 3435 (w), 3056, 2228, 1616, 1491, 1444, 796, 765, 701 cm^-1.
Ethyl 4-(Cyclohexa-1,5-dienyl)benzoate ( 4j): ¹H NMR (300 MHz, CDCl₃): δ = 7.92 (unresolved d, J = 8.4 Hz, 2 H), 7.36 (unresolved d, J = 8.4 Hz, 2 H), 6.26 (dq, J = 9.7 Hz, J = 1.8 Hz, 1 H), 6.11 (unresolved t, J = 4.4 Hz, 1 H), 5.93-6.01 (m, 1 H), 4.30 (q, J = 7.1 Hz, 2 H), 2.23-2.33 (m, 2 H), 2.09-2.19 (m, 2 H), 1.32 (t, J = 7.1 Hz, 3 H). ¹³C (75 MHz, CDCl₃): δ = 166.9, 145.3, 135.6, 130.1, 129.2, 128.6, 125.5, 125.4, 125.3, 61.2, 23.3, 22.2; 14.7. HRMS: m/z calcd: 228.1150; found: 228.1135. MS (EI, 70 eV): m/z (%) = 228 (100), 200 (10), 183 (32), 155 (87), 153 (19), 128 (10).
1-(Cyclohexa-1,5-dienyl)-3-(trifluoromethyl)benzene ( 4k): ¹H NMR (300 MHz, CDCl₃): δ = 7.54 (s, 1 H), 7.30-7.52 (m, 3 H), 6.22 (dq, J = 9.7 Hz, J = 1.8 Hz, 1 H), 6.06 (tt, J = 4.6 Hz, J = 1.3 Hz, 1 H), 5.98 (dtd, J = 9.7 Hz, J = 4.3 Hz, J = 0.9 Hz, 1 H), 2.23-2.33 (m, 2 H), 2.09-2.19 (m, 2 H). ¹³C NMR (75 MHz, CDCl₃): δ = 141.8, 135.3, 129.2, 129.0, 128.8, 125.4, 124.8, 123.8, 122.6, 23.2, 22.2. HRMS: m/z calcd: 224.0813; found: 224.0839. MS (EI, 70 eV): m/z (%) = 224 (82), 223 (32), 209 (58), 183 (87), 155 (100).
1-(Cyclohexa-1,5-dienyl)naphthalene ( 4l): ¹H NMR (300 MHz, CDCl₃): δ = 7.90-7.98 (m, 1 H), 7.73-7.79 (m, 1 H), 7.68 (d, J = 8.0 Hz, 1 H), 7.32-7.43 (m, 3 H), 7.24 (dd, J = 7.1 Hz, J = 1.3 Hz, 1 H), 6.1 (dq, J = 9.7 Hz, J = 1.8 Hz, 1 H), 5.82-5.93 (m, 2 H), 2.29-2.39 (m, 2 H), 2.18-2.29 (m, 2 H). ¹³C NMR (75 MHz, CDCl₃): δ = 140.8, 136.7, 134.1, 131.8, 128.8, 128.7, 127.7, 126.4, 126.4, 126.0, 126.05, 125.98, 125.9, 125.8, 23.2, 22.4. HRMS: m/z calcd: 206.1096; found: 206.1078. MS (EI, 70 eV): m/z (%) = 207 (15), 206 (100), 205(90), 178 (53), 165 (49).