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D. A. Flosser, R. A. Olofson / Tetrahedron Letters 43 (2002) 4275–4279
dibromides, the sample of pure 2-fluorooctane was
isolated by vacuum distillation. The published [h]2D0 (c,
3–20, CHCl3) for pure R-(−)-2-fluorooctane is –14.8.25
In the present experiment, the found value for the
2-fluorooctane was –12.7 (c 10.0, CHCl3), which trans-
lates to an optical purity of 88% (94% R,6% S) if the
literature is correct.26
York, 1991; Vol. 6, pp. 216–217.
4. DAST=Diethylaminosulfur trifluoride. Middleton, W. J.
J. Org. Chem. 1975, 40, 574–578. FAR=2-chloro-1,1,2-
trifluoroethylamine.1
5. Nakanishi, S.; Myers, T. C.; Jensen, E. V. J. Am. Chem.
Soc. 1955, 77, 3099–3100, 5033–5034.
6. Olofson, R. A.; Dang, V. A.; Morrison, D. S.; De Cusati,
P. F. J. Org. Chem. 1990, 55, 1–3.
7. (a) Dang, V. A. Ph.D. Thesis, The Pennsylvania State
University, 1986; (b) Dang, V. A.; Olofson, R. A.; Wolf,
P. R.; Piteau, M. D.; Senet, J.-P. G. J. Org. Chem. 1990,
55, 1847–1851; (c) Dang, V. A.; Olofson, R. A. J. Org.
Chem. 1990, 55, 1851–1854.
Thus, at least 88% of 25 would seem to be formed by
an SN2 displacement with inversion of configuration at
the chiral center. The remaining 12% of reaction proba-
bly occurs by an SN1 process (less if the departing
fluoroformate releases fluoride as an ion pair). Whether
the alkene side products are the result of diversion of
the SN1 cation to an E1 elimination or are formed by a
competing E2 elimination cannot be discerned. It is
noteworthy that, while DAST gives 2-fluorooctane in
97.6% optical purity, this is overshadowed by the 50%
elimination seen in that reaction.25 The stereochemical
result in the same FAR process is 88%,25 identical to
our value.
8. Fawcett, F. S.; Tullock, C. W. US Pat. 3,088,975 (May 7,
1963); Chem. Abstr. 1963, 59, 4821b.
9. Roestamadji, J.; Mobashery, S. In Encyclopedia of Reagents
for Organic Synthesis; Paquette, L. A., Ed.; John Wiley and
Sons: Chichester, 1995; Vol. 1, pp. 575–576.
10. Cotarca, L.; Delogu, P.; Nardelli, A.; Sunjic, V. Synthesis
1996, 553–576.
11. Damle, S. B. Chem. Eng. News 1993, 71 (6), 4.
12. Goren, Z.; Heeg, M. J.; Mobashery, S. J. Org. Chem. 1991,
56, 7186–7188.
A useful new process for converting alcohols to the
corresponding fluorides via fluoroformate intermediates
has been described. An attractive feature is the initial
fluoroformate synthesis which is essentially quantitative
and affords undistilled product pure enough to use in
subsequent reactions. Since fluoroformates have uses in
synthesis beyond the methodology outlined here,6,7,17
this step has value in itself. Finally, the introduction of
HBGF, a highly active and potentially low cost ‘naked
fluoride’ catalyst, is worth highlighting. A major advan-
tage of HBGF is its substantially greater thermal stabil-
ity than tetraalkylammonium fluoride catalysts, a
feature which should encourage the exploration of its
further applications.
13. Senet, J.-P. The Recent Advance in Phosgene Chemistry 1;
L’Imprimerie GPA a` Nanterre: France, 1997; 2;
L’Imprimerie SIO a` Paris: France, 1999.
14. (a) Olofson, R. A.; Lawson, A. P.; Rayle, H. L. Eur. Pat.
Appl. EP 546,930 (Jun. 16, 1993); Chem. Abstr. 1993, 119,
225691b; US Pat. 5,283,358 (Feb. 1, 1994); (b)
Kreutzberger, C. B.; Olofson, R. A.; Senet, J.-P. Fr.
Demande FR 2,703,046 (Sep. 30, 1994); Chem. Abstr. 1995,
122, 105435m; (c) Lawson, A. P. Ph.D. Thesis, The
Pennsylvania State University, 1991; (d) Blasser, J. E. Ph.D.
Thesis, The Pennsylvania State University, 1993.
15. Harmon, K. M.; Southworth, B. A.; Wilson, K. E.; Keefer,
P. K. J. Org. Chem. 1993, 58, 7294–7295.
16. A solution of 18-crown 6 (3.0 mmol) in CH3CN (20 mL)
was dripped into a stirred mixture of 1 (0.027 mol) and
spray-dried KF (0.20 mol) in CH3CN (30 mL) (ice bath).
The flask was topped by a dry ice/acetone condenser. As
it formed, the COF2 passed via the condenser to the bottom
of a stirred 0°C collector containing 1-octanol (0.0408 mol)
and dried KF (0.078 mol) in 10 mL of ether. After 2–3 h,
no alcohol remained (1H NMR) and remaining gases were
flushed away with N2. The KHF2 and excess KF were
filtered off through a silica gel plug which then was washed
with 3×10 mL ether. Rotary evaporation of the filtrate (30
min at rt) afforded 3 in 100% yield (plus trace, 1.6%, ether)
which was used in the next step without further purification.
17. (a) Cuomo, J.; Olofson, R. A. J. Org. Chem. 1979, 44,
1016–1017; (b) Olofson, R. A.; Cuomo, J. Tetrahedron Lett.
1980, 21, 819–822.
18. A reaction flask charged with HBGF (7 mol% versus 3)
attached to a small distillation apparatus topped with a
septum was stirred overnight at 80°C (oil bath) under a
vacuum of <1 mm of Hg. Dried N2 was released into the
system to exclude moisture and neat 3 (undistilled) was
syringed in through the septum. Next, water was run
through the condenser, the receiver was immersed in a dry
ice/acetone bath at –50°C, and the temperature of the oil
bath increased to 125°C. A little 1-fluorooctane19 (17)
distilledasitformed. Afteranhour, theoilbathtemperature
was increased and the remaining 17 distilled into the chilled
receiver (89% yield from 1-octanol).
Acknowledgements
We thank Dr. J.-P. Senet of SNPE for the HBGCl and
Dr. C. Kreutzberger of PPG Industries for 1.
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