LETTER
2-(Perfluoroalkyl)ethyl Triflates
687
(12) Preparation of 2-(perfluorooctyl)ethyl triflate (11b): The flask
was charged with dry CH2Cl2, cooled to -10 °C and triflic
anhydride (3.04 g, 10.7 mmol) was added to it. After 5 min, a
mixture of 2-(perfluorooctyl)ethanol (10b, 5.00 g, 10.7
mmol), dry pyridine (0.79 g, 10 mmol), dry CH2Cl2 (50 mL)
and dry hexane (50 mL) was slowly (40 min) introduced into
the mixture while cooled and stirred. Stirring and cooling were
maintained for another 40 min, followed by removal of salts
by filtration and purification of the crude triflate through short
column of silica (eluent: CH2Cl2). Removal of solvents in
vacuo afforded 4.60 g of solid fluorotriflate 11b (yield
71.6%), which was recrystallized from hexane (white crystals,
m.p. 40-42 °C).
(13) Fife, W. K.; Ranganathan, P.; Zeldin, M. J. Org. Chem. 1990,
55, 5610.
(14) Iwahara, M. JP 07179384 1996; Chem. Abstr. 1996, 124,
8394.
(15) Preparation of bis[(2-perfluorohexyl)ethyl]cyclopentadiene
(9a): The flask was charged with dry THF (50 mL) and [(2-
perfluoro-hexyl)ethyl]cyclopentadiene (8a, 1.50 g, 3.63
mmol). The mixture was cooled while stirred to -80 °C and
BuLi (2.2 mL, 3.9 mmol) was syringed to it. Stirring was
continued for 15 min at -80 °C to r.t. and the mixture was
cooled back to -80 °C, followed by addition of 2-(perfluoro-
hexyl)ethyl triflate (11a, 2.30 g, 4.63 mmol). The mixture was
then refluxed for 16 h. After removing the solvents in vacuo,
bis(polyfluoroalkylated) cyclopentadiene 9a (1.59 g, 57.7%)
was obtained by column chromatography (eluent: hexane, RF
0.9) as a yellowish oil.
Scheme 5
(16) NMR of 1,2-bis[2-(perfluorohexyl)ethyl]cyclopenta-1,3-
diene (9aA): 1H NMR 2.23 (m, 4H), 2.56 (m, 4H), 2.88 (t,
2H, J = 1.2 Hz), 6.26 (d, 1H, 3JHH = 5.5 Hz), 6.28 (d, 1H,
3JHH = 5.5 Hz, J = 1.2 Hz); 13C NMR 17.9 (s, 1C), 21.3 (s,
1C), 30.4 (m, 2C), 43.2 (s, 1C), 108.3-121.5 (m, 12C), 131.7
(s, 1C), 133.7 (s, 1C), 138.1 (s, 1C), 143.9 (s, 1C); 19F NMR
-81.5 (t, 6F, 3JFF = 10 Hz); -115.2 (m, 4F); -122.4 (m, 4F); -
123.4 (m, 4F); -124.0 (m, 4F); -126.7 (m, 4F).
(17) NMR of 1,3-bis[2-(perfluorohexyl)ethyl]cyclopenta-1,3-
diene (9aB): 1H NMR 2.23 (m, 4H), 2.56 (m, 4H), 2.84
(quintet, 2H, J = 1.8 Hz), 5.87 (sextet, 1H, J = 1.6 Hz), 6.04
(m, 1H); 13C NMR 20.6 (s, 1C), 21.3 (s, 1C), 30.4 (m, 2C),
42.9 (s, 1C), 108.3-121.5 (m, 12C), 125.0 (s, 1C), 129.0 (s,
1C), 143.9 (s, 1C), 147.2 (s, 1C); 19F NMR -81.5 (t, 6F,
3JFF = 10 Hz); -115.2 (m, 4F); -122.4 (m, 4F); -123.4 (m, 4F);
-124.0 (m, 4F); -126.7 (m, 4F).
(18) NMR of 1,4-bis[2-(perfluorohexyl)ethyl]cyclopenta-1,3-
diene (9aC): 1H NMR 2.23 (m, 4H), 2.56 (m, 4H), 2.83
(sextet, 2H, J = 1.8 Hz), 6.04 (m, 2H); 13C NMR 18.5 (s, 2C),
30.4 (m, 2C), 39.5 (s, 1C), 108.3-121.5 (m, 12C), 127.9 (s,
2C), 143.8 (s, 2C); 19F NMR -81.5 (t, 6F, 3JFF = 10 Hz); -
115.2 (m, 4F); -122.4 (m, 4F); -123.4 (m, 4F); -124.0 (m, 4F);
-126.7 (m, 4F).
(19) NMR of 2,3-bis[2-(perfluorohexyl)ethyl]cyclopenta-1,3-
diene (9aD): 1H NMR 2.23 (m, 4H), 2.56 (m, 4H), 2.79 (t,
2H, J = 1.1 Hz), 6.02 (quintet, 2H, J = 0.9 Hz); 13C NMR
21.3 (s, 2C), 30.4 (m, 2C), 44.7 (s, 1C), 108.3-121.5 (m, 12C),
127.3 (s, 2C), 143.9 (s, 2C); 19F NMR -81.5 (t, 6F, 3JFF = 10
Hz); -115.2 (m, 4F); -122.4 (m, 4F); -123.4 (m, 4F); -124.0
(m, 4F); -126.7 (m, 4F).
References and Notes
(1) Horváth, I. T.; Rábai, J. Science 1994, 266, 72.
(2) Horváth, I. T. Acc. Chem. Res. 1998, 31, 641; Hope, E. G.;
Stuart, A. M. J. Fluorine Chem. 1999, 100, 75; Fish, R. H.
Chem.-Eur. J. 1999, 5, 1677
(3) Kainz, S.; Koch, D.; Baumann, W.; Leitner, W. Angew. Chem.
Int. Ed. Engl. 1997, 36, 15.
(4) Barthel-Rosa, L. P.; Gladysz, J. A. Coord. Chem. Rev. 1999,
190-192, 587; Szlavik, Z.; Tarkanyi, G.; Tarczay, G.;
Gomory, A.; Rabai, J. J. Fluorine Chem. 1999, 98, 83.
(5) Horváth, I. T.; Le Husebo, T.; Hughes, R. P. Inorg. Chem.
Commun. 1998, 1, 197.
(6) Hughes, R. P.; Trujillo, H. A. Organometallics 1996, 15, 286.
(7) The details of this strategy will be reported: Bríza T.; Kvícala
J.; Paleta O.; Cermák J J. Fluorine Chem., in preparation.
(8) Formation of bis(polyfluoroalkylated) cyclopentadienes 9 in
small amounts as side-products in the preparation of
mono(polyfluoroalkylated) cyclopentadienes 8 by the PTC
method has been reported in the literature.6
(9) NMR of 2-(perfluorohexyl)ethyl triflate (11a): 1H NMR
2.67 (m, 2H), 4.78 (m, 2H); 19F NMR -75.4 (s, 3F), -81.6 (t,
2F, J = 10 Hz), -114.0 (m, 2F), -122.1 (m, 2F), -123.2 (m, 2F),
-123.9 (m, 2F), -126.2 (m, 2F).
(10) NMR of 2-(perfluorooctyl)ethyl triflate (11b): 1H NMR 2.68
(m, 2H), 4.79 (m, 2H); 19F NMR -75.1 (s, 3F), -81.3 (t, 2F,
J = 10 Hz), -114.0 (m, 2F), -122.1 (m, 2F), -123.2 (m, 4F), -
123.9 (m, 2F), -126.6 (m, 2F).
(11) We thank Elf Atochem Co. for generous gift of fluorinated
iodides and alcohols.
(20) Kví ala, J.; Mysík, P., Paleta, O. Synlett, 2001, 547.
Article Identifier:
1437-2096,E;2001,0,05,0685,0687,ftx,en;G00601ST.pdf
Synlett 2001, No. 5, 685–687 ISSN 0936-5214 © Thieme Stuttgart · New York