A General Method for the Synthesis of 2,2-[60]Fullerenoalkanals: The Reaction of [60]Fullerene with 2-Bromoenol Silyl Ethers

Abstract

Five kinds of 2,2-[60]fullerenoalkanals were synthesized by the fluoride ion-mediated reaction of [60]fullerene with 2-bromoenol silyl ethers, which were easily prepared by 2-bromination of the corresponding enol silyl ethers. The reactivity differed significantly depending on the stability of the 2-bromoenol silyl ethers. High yield and selectivity were achieved for the reaction of 2-bromoenol trimethylsilyl ethers under mild conditions (KF/18-crown-6-ether). The reaction of stable 2-bromoenol tert-butyldimethylsilyl ethers, on the other hand, required the use of more reactive tetra­butylammonium fluoride as a fluoride ion source.

Key words

fullerenes - cyclopropanation - silyl enol ethers - aldehydes - bromine

References and Notes

• 2a Guldi D. Martin N. Fullerenes: From Synthesis to Optoelectronic Properties   1st ed.:  Springer; Berlin: 2002. 
• 2b Hirsch A. Brettreich M. Fullerenes: Chemistry and Reactions   1st ed.:  Wiley-VCH; Weinheim: 2005. 
• 3a Wudl F. Acc. Chem. Res.  1992,  25:  157 
• 3b Bingel C. Chem. Ber.  1993,  126:  1957 
• 3c Maggini M. Scorrano G. Prato M. J. Am. Chem. Soc.  1993,  115:  9798 
• 3d Ganapathi PS. Rubin Y. J. Org. Chem.  1995,  60:  2954 
• 3e Sawamura M., Iikura H., Nakamura E.; J. Am. Chem. Soc.; 1996, 118: 12850
• For selected examples of recent methods for the preparation of functionalized [60]fullerenes, see:
• 4a Chen Z. Wang G. J. Org. Chem.  2005,  70:  2380 
• 4b Wang G. Li F. Zhang T. Org. Lett.  2006,  8:  1355 
• 4c Li F. Liu T. Wang G.
  J. Org. Chem.  2008,  73:  6417 
• 4d Tzirakis MD. Orfanopoulos M. J. Am. Chem. Soc.  2009,  131:  4063 
• 5 Hamada M. Hino T. Kinbara K. Saigo K. Tetrahedron Lett.  2001,  42:  5069 
• 6a Ito H. Ishida Y. Saigo K. Tetrahedron Lett.  2005,  46:  8757 
• 6b Ito H. Ishida Y. Saigo K. Tetrahedron Lett.  2006,  47:  3095 
• 6c Ito H. Ishida Y. Saigo K. J. Org. Chem.  2006,  71:  4759 
• 7 Wang G. Lu Y. Chen Z. Wu S. J. Org. Chem.  2009,  74:  4841 
• 8 Hino T. Kinbara K. Saigo K. Tetrahedron Lett.  2001,  42:  5065 
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• 16 Jung ME. Nishimura N. Org. Lett.  2001,  3:  2113 

1

Present address: School of Environmental Science and Technology, Koch University of Technology, Miyanokuchi, Tosayamada-cho, Kami-shi, Kochi 782-8502, Japan

10

General procedure for the synthesis 2-bromoenol trimethyl-silyl ethers 1a-e. Bromine (1.9 mL, 37 mmol) and triethyl-amine (7.7 mL, 55 mmol) were successively added dropwise to a solution of 1-trimethylsiloxy-1-alkene (37 mmol) in CH₂Cl₂ (28 mL) at -78 ˚C, and the mixture was stirred at r.t. for 3 h. Then, hexane (30 mL) was added to the mixture, and the resultant white precipitates were filtered off. The filtrate was washed with saturated NaHCO₃ (100 mL), H₂O (100 mL) and brine (100 mL), successively. The organic layer was dried over sodium sulfonate and filtered, and the solvent was removed under reduced pressure. The residue was purified by distillation under reduced pressure to afford the corresponding 2-BrESE (E/Z mixture) as a clear liquid.
2-Bromo-1-trimethylsiloxy-1-butene (1a): Ratio major/minor = 89:11 (determined by ^¹H NMR). Bp 63-73 ˚C/15 mmHg. IR (neat): 2969, 2937, 2917, 2876, 2804, 1656, 1457, 1336, 1317, 1255, 1191, 1129, 1106, 1068, 1041, 942, 924, 867, 846, 754 cm^-¹. ^¹H NMR (300 MHz, CDCl₃):
δ (major) = 6.47 (t, J = 0.6 Hz, 1 H), 2.5-2.4 (m, 2 H), 1.1-1.0 (m, 3 H), 0.3-0.2 (m, 9 H); δ (minor) = 6.15 (t, J = 0.6 Hz, 1 H), 2.5-2.4 (m, 2 H), 1.1-1.0 (m, 3 H), 0.3-0.2 (m, 9 H). ^¹³C NMR (75 MHz, CDCl₃): δ = 135.28, 111.51, 29.24, 14.38, -0.02. MS (EI): m/z (%) = 222 (100), 224 (100). 2-Bromo-1-trimethylsiloxy-1-dodecene (1b): Ratio major/minor = 92:8 (determined by ^¹H NMR). Bp ˜124 ˚C/1 mmHg. IR (neat): 2956, 2925, 2854, 1730, 1657, 1465, 1254, 1195, 870, 848, 756 cm^-¹. ^¹H NMR (300 MHz, CDCl₃): δ (major) = 6.44 (s, 1 H), 2.43 (t, J = 6.9 Hz, 2 H), 1.89 (br, 2 H), 1.26 (br, 16 H), 0.3-0.2 (m, 9 H); δ (minor) = 6.50 (s, 1 H), 2.43 (t, J = 6.9 Hz, 2 H), 1.89 (br, 2 H), 1.26 (br, 16 H), 0.3-0.2 (m, 9 H). ^¹³C NMR (75 MHz, CDCl₃):
δ = 135.84, 35.49, 32.25, 29.94, 29.88, 29.81, 29.67, 29.63, 28.68, 28.56, 23.03, 14.47, -0.02. MS (EI): m/z (%) = 334 (100), 336 (100).
2-Bromo-3-phenyl-1-trimethylsiloxy-1-propene (1c): Ratio major/minor = 89:11 (determined by ^¹H NMR). Bp ˜112 ˚C/1.5 mmHg. IR (neat): 3029, 2958, 2900, 1731, 1659, 1603, 1495, 1454, 1419, 1333, 1254, 1210, 1172, 868, 849, 748, 698 cm^-¹. ^¹H NMR (300 MHz, CDCl₃): δ (major) = 7.3-7.2 (m, 5 H), 6.59 (t, J = 0.9 Hz, 1 H), 3.64 (s, 2 H), 0.3-0.2 (m, 9 H); δ (minor) = 7.3-7.2 (m, 5 H), 6.64 (t, J = 0.9 Hz, 1 H), 3.80 (s, 2 H), 0.3-0.2 (m, 9 H). ^¹³C NMR (75 Hz, CDCl₃): δ = 138.31, 137.19, 128.62, 128.36, 126.63, 107.44, 41.49, -0.34. MS (EI): m/z (%) = 284 (100), 226 (100).
2-Bromo-2-phenyl-1-(trimethylsiloxy)ethene (1d): Ratio major/minor = 90:10 (determined by ^¹H NMR). Bp ˜78 ˚C/1 mmHg. IR (neat): 3060, 3031, 2958, 1727, 1636, 1491, 1443, 1255, 1167, 935, 758, 694 cm^-¹. ^¹H NMR (300 MHz, CDCl₃): δ (major) = 7.5-7.2 (m, 4 H), 6.96 (s, 1 H), 0.30 (s, 9 H); δ (minor) = 6.50, 7.5-7.2 (m, 4 H), 6.90 (s, 1 H), 0.24 (s, 9 H). ^¹³C NMR (75 MHz, CDCl₃): δ = 138.50, 129.25, 129.04, 128.32, 127.62, 127.37, -0.27. MS (EI): m/z (%) = 270 (100), 272 (100).
2-Bromo-1-trimethylsiloxyethene (1e): Bp ˜74 ˚C/52 mmHg. IR (neat): 3106, 3010, 2960, 2901, 1636, 1329, 1255, 1241, 1166, 1094, 878, 849, 757, 708, 655, 605 cm^-¹. ^¹H NMR (300 MHz, CDCl₃): δ = 6.73 (d, J = 3.9 Hz, 1 H), 5.24 (d, J = 3.9 Hz, 1 H), 0.24 (s, 9 H). ^¹³C NMR (75 MHz, CDCl₃): δ = 141.41, 87.37, -0.43. MS (EI): m/z (%) = 194 (100), 196 (100)

11

The enol tert-butyldimethylsilyl ethers 4c′ and 4d′ were synthesized according to a method in the literature,^¹6 and was purified by silica gel column chromatography.
1- tert -Butyldimethylsilyloxy-3-phenylpropene (4c′): IR(neat): 3029, 2955, 2929, 2858, 1655, 1255, 1115, 838 cm^-¹. ^¹H NMR (300 MHz, CDCl₃): δ = 7.4-7.1 (m, 5 H), 6.30 (dt, J = 5.7, 1.5 Hz, 1 H), 4.67 (dt, J = 5.7, 7.2 Hz, 1 H), 3.45 (dd, J = 1.5, 7.2 Hz, 2 H), 0.94 (s, 9 H), 0.15 (s, 6 H). ^¹³C NMR (75 MHz, CDCl₃): δ = 141.97, 139.10, 128.32, 128.25, 125.58, 109.08, 29.92, 25.63, 18.26, -5.33. MS (EI): m/z = 248. 1- tert -Butyldimethylsilyloxy-2-phenylethene (4d′): Ratio major/minor = 52:48 (determined by ^¹H NMR). IR (neat): 3030, 2955, 2930, 2885, 2858, 1645, 1471, 889, 838, 783, 692 cm^-¹. ^¹H NMR (300 MHz, CDCl₃): δ (major) = 7.3-7.1 (m, 5 H), 7.00 (d, J = 12.3 Hz, 1 H), 6.03 (d, J = 12.3 Hz, 1 H), 0.96 (s, 9 H), 0.21 (s, 6 H); δ (minor) = 7.7-7.6 (m, 2 H), 7.3-7.1 (m, 3 H), 6.42 (d, J = 6.6 Hz, 1 H), 5.30 (d, J = 6.6 Hz, 1 H), 0.98 (s, 9 H), 0.22 (s, 6 H). ^¹³C NMR (75 MHz, CDCl₃): δ = 142.23, 140.51, 136.47, 136.19, 128.49, 128.18, 128.07, 125.73, 125.63, 125.12, 112.82, 108.84, 25.68, 25.62, 18.32, 18.21, -5.18, -5.38. MS (EI): m/z = 234

12

The 2-bromoenol tert-butyldimethylsilyl ethers 1c′ and 1d′ were synthesized in a similar manner to that used for the preparation of the 2-boromoenol trimethylsilyl ethers. The crude products were purified by column chromatography [SiO₂; hexane-CH₂Cl₂, 10:0 to 8:2 (v/v)].
2-Bromo-1- tert -butyldimethylsilyloxy-3-phenylpropene (1c′): IR(neat): 3029, 2954, 2929, 2858, 1659, 1254, 1211, 1171, 838 cm^-¹. ^¹H NMR (300 MHz, CDCl₃): δ = 7.4-7.2 (m, 5 H), 6.61 (s, 1 H), 3.64 (s, 2 H), 0.96 (s, 1 H), 0.19 (s, 1 H). ^¹³C NMR (75 MHz, CDCl₃): δ = 138.38, 137.72, 128.63, 128.34, 126.61, 106.92, 441.42, 25.51, 18.27, -5.17. MS (EI): m/z (%) = 326 (100), 328 (100). 2-Bromo-1- tert -butyldimethylsilyloxy-2-phenylethene (1d′): Ratio major/minor = 65:35 (determined by ^¹H NMR). Major isomer: IR (neat): 2954, 2929, 2858, 1635, 1261, 1168, 828 cm^-¹. ^¹H NMR (300 MHz, CDCl₃): δ = 7.5-7.4 (m, 2 H), 7.4-7.2 (m, 3 H), 6.98 (s, 1 H), 0.99 (s, 1 H), 0.24 (s, 1 H). ^¹³C NMR (75 MHz, CDCl₃): δ = 138.91, 137.11, 128.31, 127.53, 127.32, 106.74, 25.50, 18.26, -5.11. MS (EI): m/z (%) = 312(100), 314(100). Minor isomer: IR(neat): 2955, 2929, 2858, 1617, 1259, 1228, 1136, 827 cm^-¹. ^¹H NMR (300 MHz, CDCl₃): δ = 7.8-7.7 (m, 2 H), 7.4-7.1 (m, 3 H), 6.91 (s, 1 H), 0.91 (s, 9 H), 0.19 (s, 6 H). ^¹³C NMR (75 MHz, CDCl₃): δ = 140.24, 135.50, 128.99, 127.74, 127.31, 106.93, 25.44, 18.07, -5.30. MS (EI): m/z (%) = 312 (100), 314 (100)

13

General procedure for the synthesis of 2,2-[60]fullereno-alkanals. The KF/18-crown-6 method: KF (5.8 mg, 0.10 mmol) and an 18-crown-6 solution in toluene (0.10 M, 0.20 mL, 0.020 mmol) were added to a solution of [60]fullerene (72 mg, 0.10 mmol) and 2-BrESE (0.10 mmol) in toluene (72 mL). After the mixture was stirred at r.t. for 72 h, the solvent was evaporated to dryness. The residue was purified by preparative thin layer chromatography (SiO₂, CS₂) to afford the corresponding 2,2-[60]fullerenoalkanal as a dark-brown solid.
The TBAF method: A TBAF solution (1 M in THF, 0.30 mL, 0.30 mmol) was added to a solution of [60]fullerene (72 mg, 0.10 mmol) and 2-BrESE (0.10 mmol) in toluene (72 mL). After the mixture was stirred at r.t. for 3 h, the solvent was evaporated to dryness. The residue was purified by column chromatography [SiO₂; hexane-toluene, 9:1 to 2:1 (v/v)] to afford the corresponding 2,2-[60]fullerenoalkanal as a dark-brown solid.
2,2-[60]Fullerenobutanal (2a): See ref. 5.
2,2-[60]Fullerenododecanal (2b): IR (KBr): 2921, 2849, 1719, 1461, 1428, 1186, 578, 555, 526 cm^-¹. ^¹H NMR (300 MHz, CDCl₃): δ = 10.57 (s, 1 H), 2.79 (t, J = 8.1 Hz, 2 H), 2.02-1.85 (m, 2 H), 1.66-1.18 (m, 14 H), 0.89 (t, J = 6.6 Hz, 3 H). ^¹³C NMR [125 MHz, CDCl₃/CS₂, 1:1 (v/v)]: δ = 194.24, 146.84, 145.79, 145.26, 145.25, 145.23, 145.16, 145.13, 144.97, 144.70, 144.64, 144.62, 144.60, 144.40, 143.76, 143.69, 143.19, 143.08, 143.01, 142.94, 142.92, 142.91, 142.05, 141.98, 141.97, 141.57, 141.10, 141.04, 137.96, 137.83, 75.17, 50.23, 31.99, 30.05, 29.71, 29.69, 29.55, 29.46, 27.70, 25.87, 22.84, 14.23. MS (MALDI-TOF): m/z [M] ^{˙ +} calcd for C₇₂H₂₂O: 902.17; found: 902.11.
2,2-[60]Fullereno-3-phenylpropanal (2c): IR (KBr): 2922, 2850, 1718, 1494, 1427, 1260, 1186, 1073, 1030, 732, 706, 576, 555, 526 cm^-¹. ^¹H NMR (300 MHz, CDCl₃): δ = 10.55 (s, 1 H), 7.58 (d, J = 7.4 Hz, 2 H), 7.38 (dd, J = 7.4, 7.4 Hz, 2 H), 7.30 (d, J = 7.4 Hz, 1 H), 4.23 (s, 2 H). ^¹³C NMR [125 MHz, CDCl₃/CS₂, 1:1 (v/v)]: δ = 193.83, 146.85, 145.61, 145.38, 145.35, 145.28, 145.27, 144.98, 144.82, 144.81, 144.80, 144.78, 144.76, 144.58, 143.88, 143.78, 143.20, 143.18, 143.06, 143.01, 142.17, 142.10, 142.07, 141.62, 141.24, 138.15, 138.12, 136.77, 129.40, 128.95, 127.25, 74.98, 50.15, 31.56; three peaks are overlapped. MS (MALDI-TOF): m/z [M] ^{˙ +} calcd for C₆₉H₈O: 852.06; found: 851.80.
2,2-[60]Fullereno-2-phenylethanal (2d): See ref. 7.
2,2-[60]Fullerenoethanal (2e): See ref. 7.

14

[60]Fullerene derivatives having two or more alkanal moieties were obtained as by-products.

15

Br₂ (0.40 M in CH₂Cl₂, 1.25 mL, 0.50 mmol) and Et₃N (1.5 M in CH₂Cl₂, 0.50 mL, 0.75 mmol) were successively added dropwise to a solution of 1-trimethylsilyloxy-1-butene (4a; 72 mg, 0.50 mmol) in CH₂Cl₂ (7.5 mL) at -78 ˚C, and the mixture was stirred at r.t. for 3 h. A solution of [60]fullerene (0.10 mM in toluene, 72 mL), KF (29 mg, 0.50 mmol), and 18-crown-6 (26 mg, 0.10 mmol) were successively added to the mixture. After the mixture was stirred at r.t. for 42 h, the solvent was evaporated to dryness. The residue was purified by preparative thin layer chromatography (SiO₂, CS₂) to afford 2,2-[60]fullerenobutanal 1a (36 mg, 0.46 mmol, 46% yield) as a dark-brown solid