5114 J . Org. Chem., Vol. 61, No. 15, 1996
Lindner and Lemal
of water. The residual bromine was quenched with 10 mL of
a saturated solution of sodium thiosulfate, and the product
was extracted with 3-15 mL portions of diethyl ether. The
solvents were removed first on a rotary evaporator and then
with a vacuum pump at 1 Torr. Analysis of the 1H NMR
spectrum revealed 0.6 equiv of acetonitrile complexed to the
hydroxyl groups. Otherwise, the compound was shown to be
pure by 19F NMR spectroscopy: 7.6 g (88% yield) of a light
yellow oil. 19F NMR (CD2Cl2): Φ -107.1 (d of d, J ) 245, 16
Hz, 1F); -121.2 (d of d, J ) 236, 17 Hz, 1F); -122.0, -125.6
(AB q, J ) 247 Hz, 2F); -131.2 (d, J ) 245, 1F); -132.0 (d, J
) 236 Hz, 1F); -132.9 (m, 1F). 1H NMR (CD2Cl2): δ 3.8 (bs,
2H); 2.01 (s, 2H). IR (thin film, cm-1): 3000-3600 (br), 1320,
1289, 1217, 1187, 1120, 1077, 1023, 958, 835, 805.
2-Br om op er flu or ocyclop en ta n on e (6). To an NMR tube
containing 50 mg of diol 5 and 0.5 mL of chloroform-d was
added 0.1 mL of concentrated sulfuric acid. The tube was
shaken vigorously for 20 min, and the 19F NMR spectrum
indicated that formation of ketone 6 was complete. 19F NMR
(CDCl3): Φ -119.9, -122.6 (AB q, J ) 296 Hz, 2F); -122.7
(d, J ) 258 Hz, 1F); -124.3, -128.9 (AB q, J ) 250 Hz, 2F);
-137.3 (d, J ) 258 Hz, 1F); -149.4 (m, 1F). IR (CDCl3, cm-1):
1805, 1338, 1313, 1259, 1189, 1100, 1033, 1009, 980, 834.
2 -B r o m o -1 , 1 -b i s ( t r i m e t h y l s i l o x y ) p e r f l u o r o -
cyclop en ta n e (8). To a dry 25 mL round-bottom flask
equipped with a Teflon stir bar were added 3 mL of N,O-bis-
(trimethylsilyl)acetamide (12 mmol) and 10 mL of methylene
chloride. At ambient temperature, 1.0 g (3.3 mmol) of diol 5
dissolved in 5 mL of methylene chloride was added dropwise
to the reaction vessel. After 15 min the reaction mixture was
washed with one 10 mL portion of water, and the methylene
chloride layer was dried over MgSO4. The solution was
concentrated, and the resulting liquid was passed through a
silica gel column to remove residual silating agent, with
methylene chloride as the eluting solvent. After removal of
the solvent in vacuo, the residue was distilled at 60-62 °C/
1.5 Torr to give 8 as a clear, colorless liquid (1.1 g, 74% yield).
19F NMR (CDCl3): Φ -106.3 (d, J ) 244 Hz, 1F); -118.0 (d, J
) 235 Hz, 1F); -121.2, -126.5 (AB q, J ) 250 Hz, 2F); -130.4
(d, J ) 244 Hz, 1F); -130.4 (m, 1F); -132.5 (d, J ) 235 Hz,
1F). 1H NMR (CDCl3): δ 0.30 (s, 9H); 0.24 (s, 9H). MS m/ e:
345, 343 (C8H10BrF6OSi+), 147 (C5H15OSi+); 73 (Me3Si+). Anal.
Calcd for C11H18F7Si2O2Br: C, 29.27; H, 4.01; F, 29.47.
Found: C, 29.18; H, 4.07; F, 29.53.
solvents by virtue of its strength as a hydrogen bond
donor, but is only present to the extent of 13% in carbon
tetrachloride. Quantum mechanical calculations suggest
that the difference in the two systems is attributable to
greater ketone destabilization of 1k than 2k relative to
cyclopentanone. We are currently in the process of
extending this study of keto-enol relationships to highly
fluorinated acyclic systems. The contrasting results will
be reported shortly.
Exp er im en ta l Section
19F NMR spectra were recorded at 282.2 MHz. Trichloro-
fluoromethane was used as an internal standard, and all
chemical shifts are reported on the Φ scale (ppm from internal
1
trichlorofluoromethane, upfield negative). The H NMR spec-
tra were recorded at 300 MHz. Tetramethylsilane was used
as an internal standard and chemical shifts are reported on
the δ scale.
Carbon tetrachloride was distilled from phosphorus pen-
toxide and acetonitrile from calcium hydride. Diethyl ether
and tetrahydrofuran were distilled from potassium benzophe-
none ketyl. Perfluorocyclopentene was prepared from oc-
tachlorocyclopentene according to literature methods.20 Where
noted, Pyrex reaction vessels and NMR tubes were silated with
refluxing N,O-bis(trimethylsilyl)acetamide, followed by several
acetone rinses. The glassware was then dried in an oven for
a minimum of 6 h at 140 °C.
Analytical gas chromatograms were obtained on a 25 m
methyl silicone capillary column with flame ionization detector.
The standard program was as follows: carrier pressure 25
p.s.i.; injector 150 °C; detector 200 °C; column temperature is
noted in text. Isolation of pure compounds was done by
preparative GC using a thermal conductivity detector. The
column used was 25 ft × 1/4 in., 20% QF-1 on 80/100 mesh
Chromosorb-W HP. The standard program was as follows:
injector 190 °C; detector 210 °C; column temperature is noted
in text. Elemental analyses were performed by Schwarzkopf
Microanalytical Laboratory, Woodside, NY 11377. Isolated
yields were corrected for purity.
The quantum mechanical calculations were performed on
Gaussian 92, Revision C.3.21 Vibrational frequencies were
calculated at the HF/6-31G** level of theory and were scaled
by 0.893.22 The electrostatic point charges were calculated
with the Spartan package of programs.23
2H-P er flu or ocyclop en ta n e-1,1-d iol (10). Enol 1e (4.3 g,
0.020 mol) was statically transferred at 25 °C/30 mTorr to a
100 mL round-bottom flask containing 50 mL of acetonitrile.
The contents of the reaction vessel were thawed, and then 10
mL of concentrated hydrochloric acid was added. After 2 h of
stirring at 25 °C, the reaction mixture was diluted with 20
mL of distilled water. The organic layer was extracted with
3-25 mL portions of diethyl ether and dried over magnesium
sulfate. Diethyl ether was removed on a rotary evaporator at
20 Torr to leave a milky white liquid. The reaction mixture
contained 35% of 10, 5% of 1e, and 60% of acetonitrile by 19F
and 1H NMR spectroscopy. To remove acetonitrile, 50 mL of
1,2-dichloroethane was added, and the mixture was distilled
at 10 Torr to yield 2.7 g (50% yield) of residual liquid
containing 85% of 10, 5% of 1e, and 10% of acetonitrile. 19F
NMR (CD2Cl2): Φ -116.2 (d, J ) 263 Hz, 1F); -127.2 (d, J )
263 Hz, 1F); -127.3, -129.8 (AB q, J ) 255 Hz, 2F); -131.0,
P er flu or ocyclop en ten -1-ol (1e). To a dry 50 mL round-
bottom flask containing 15 mL of 1,2,4-trichlorobenzene and
a stir bar was added 3.2 g (0.01 mol) of 1-benzoxyperfluoro-
cyclopentene.10 The reaction vessel was attached to the
vacuum line, and two U-traps cooled to -13 °C (ethylene glycol/
CO2(s)) and -78 °C (2-propanol/CO2(s)) were attached in series.
Concentrated sulfuric acid (10 mL, 0.1 mol) was added, and
the heterogeneous liquids were stirred vigorously for 15 min.
All volatile products were removed under reduced pressure
(30 mTorr) and collected in the U-traps. The -13 °C U-trap
contained only 1,2,4-trichlorobenzene, and the -78 °C U-trap
contained 1.7 g (77% yield) of enol 1e (95%) and enone 4 (5%).
The 19F and 1H NMR spectra of both compounds were
consistent with those reported elsewhere.10
2-Br om op er flu or ocyclop en ta n e-1,1-d iol (5). Freshly
prepared enol 1e (5.5 g, 26 mmol) was statically transferred
at 15 mTorr to a 25 mL round-bottom flask containing 10 mL
of dry acetonitrile. With the vessel cooled in an ice bath,
bromine (2 mL, 39 mmol) was added at once followed by 5 mL
1
-133.0 (AB q, J ) 251 Hz, 2F); -214.1 (d, J ) 45 Hz, 1F). H
NMR (CD2Cl2): δ 3.7 (s, 1H); 3.9 (s, 1H); 4.9 (d of multiplet, J
) 45.2 Hz, 1H).
2H-1,1-Bis(tr im eth ylsiloxy)p er flu or ocyclop en ta n e (9).
F r om 10. A dry 25 mL three-neck round-bottom flask
equipped with a magnetic stir bar and dropping funnel was
charged with 1.0 g (5 mmol) of N,O-bis(trimethylsilyl)aceta-
mide and 10 mL of dry methylene chloride. A solution of 85%
pure diol 10 (0.5 g, 2 mmol) in methylene chloride was added
dropwise with stirring at ambient temperature. After an
additional 30 min of stirring, the reaction mixture was passed
through a silica gel column with methylene chloride as the
eluting solvent to remove unreacted silating agent. The
methylene chloride was removed on a rotary evaporator to
leave 0.6 g of 95% pure 9 (77% yield) as a clear, colorless liquid.
(20) Maynard, J . T. J . Org. Chem. 1962, 218, 112.
(21) Gaussian 92, Revision C.3: Frisch, M. J .; Trucks, G. W.; Head-
Gordon, M.; Gill, P. M. W.; Wong, M. W.; Foresman, J . B.; J ohnson, B.
G.; Schelegel, H. B.; Robb, M. A.; Replogle, E. S.; Gomperts, R.; Andres,
J . L.; Raghavachari, K.; Binkley J . S.; Gonzalez, C.; Martin, R. L.; Fox,
D. J .; Defrees, D. J .; Baker, J .; Stewart, J . J . P.; Pople, J . A. Gaussian,
Inc.; Pittsburgh, PA, 1992.
(22) Hehre, W. J .; Radom, L.; Schleyer, P.v.R.; Pople, J . S. Ab Initio
Molecular Orbital Theory; Wiley: New York, 1986.
(23) Spartan: Hehre, W., Wavefunction, Inc., 18401 Von Karman,
Suite 370, Irvine, CA 92717.