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more electron-rich carbene complexes provide higher yields of fur-
an. This may not be a reflection of faster reactivity, but may be due
to increased stability of the product to oxidation or hydrolysis. We
furthermore observed benzannulation upon reaction of hexa-
fluoro-butyne with a vinylketene iron complex.35,37 In future work,
unsymmetrical trifluoromethylacetylenes will be examined in both
processes to establish the regioselectivity that might be exhibited.
The process reported here has significant implications on the
mechanism of reaction of alkynes with iron(0) carbene complexes
as well as on the establishment of synthetically useful protocols for
the preparation of trifluoromethylated furans and phenols.
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Acknowledgments
We thank the office of the Vice-President of Academic Affairs of
Long Island University for a research grant that allowed prelimin-
ary results to be obtained during 2007. The project described was
partially supported by NIH Grant Number SC2GM082276 from the
National Institute of General Medical Sciences. The content is so-
lely the responsibility of the authors and does not necessarily rep-
resent the official views of the National Institute of General
Medical Sciences of the National Institutes of Health. We further
thank the Chemistry Department of Rutgers University at Newark
for allowing us to use the GC–MS and NMR facility. We thank J.
Sebeo, Y. Rosner, and C. Rivera (Project SEED student) for technical
assistance.
Lett. 2006, 47, 963–966.
A substructure search on Chemical Abstracts
SciFinderÒ revealed no hits for a 2,3-bis-trifluoromethylated phenol.
35. General procedure: A heavy-walled Schlenk tube equipped with a Young Valve
and small stir bar was cooled to À78 °C and evacuated and filled with argon. A
quantity of hexafluorobutyne (500–1300 mg; 3–8 mmol) was allowed to distill
into the tube and then weighed. The tube was recooled and a solution of
carbene or vinylketene complex (0.5–1.0 mmol) in anhydrous THF (5–6 mL)
was added slowly. The mixture was placed under argon and the tube sealed
tightly. The biphasic mixture was allowed to warm to room temperature
slowly and was gradually heated at 60 °C for 48 h. The tube was then cooled to
À78 °C, the Young valve opened, and then the solution was allowed to warm to
room temperature. The crude product was filtered through Celite and then
purified via flash chromatography on triethylamine-doped silica.
Supplementary data
Supplementary data associated with this article can be found, in
36. Spectroscopic
data
(2g):
From
tetracarbonyl[4-N,N-
References and notes
dimethylaminophenyl(ethoxy)methylene] iron (243 mg; 0.73 mmol) and
hexafluorobutyne (1.2 g; 7.4 mmol) in THF (5 mL) was obtained 2g (yield:
128 mg; 48%) 1H NMR (400 MHz, acetone-d6) d 7.40 (2H, d, J = 8.8 Hz), 6.78
(2H, d, J = 8.8 Hz), 4.50 (2H, q, J = 7.2 Hz, CH2CH3), 2.99 (6H, s, N(CH3)2), 1.40
(3H, t, J = 7.2 Hz, CH3). 13C NMR (100.57 MHz, acetone-d6) d: 157.0, 151.7,
147.0, 129.6, 121.0, 120.9, 119.0, 114.6, 111.6, 69.3, 39.4, 14.4. 19F NMR
(376.3 MHz, acetone-d6) d: À56.64, À56.99. GC–MS: m/z 367(79), 338(100),
310(47), 148(37).
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37. Spectroscopic data (4): From tricarbonyl[2-ethoxy-3-phenyl-butadiene-1-one]
iron (360 mg; 1.10 mmol) and hexafluorobutyne (1.17 g; 7.22 mmol) in THF
(6 mL) was obtained 2-ethoxy, 4,5-bis(trifluoromethyl)-biphenylol 4 (yield:
147 mg; 42%) 1H NMR (400 MHz, acetone-d6) d 9.56 (1H, s, OH), 7.65 (2H, d,
J = 7.2 Hz), 7.49 (2H, t, J = 7.6 Hz), 7.45 (1H, t, J = 7.2 Hz), 7.34 (1H, s) 3.64 (2H,
q, J = 7.2 Hz), 1.06 (3H, t, J = 7.2 Hz) 13C NMR (100.57 MHz, acetone-d6) d: 152.3,
147.9, 137.5, 136.2, 128.9, 128.7, 124.8, 124.4, 122.6, 122.1, 120.2,113.0, 69.5,
14.4. 19F NMR (376.3 MHz, acetone-d6) d: À58.04, À58.85. GC–MS: 350(98),
331(50), 322(70), 301(100), 233(96), 177(45).