Facile conversion of 4,4,4-trifluorobut-2-yn-1-ols to 4,4,4-trifluorobut-2-en-1-ones

Article abstract of DOI:10.1016/j.tet.2009.05.087

Smooth isomerization of 4,4,4-trifluorinated propargylic alcohols 1 opened a new and convenient route to readily get access to the corresponding α,β-unsaturated ketones 4 just by heating a THF solution in the presence of Et₃N.

Full text of DOI:10.1016/j.tet.2009.05.087

Tetrahedron 65 (2009) 5945–5948
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journal homepage: www.elsevier.com/locate/tet
Facile conversion of 4,4,4-trifluorobut-2-yn-1-ols to 4,4,4-
trifluorobut-2-en-1-ones
*
Takashi Yamazaki , Tomoko Kawasaki-Takasuka, Atsushi Furuta, Shogo Sakamoto
Department of Applied Chemistry, Graduate School of Engineering, Tokyo University of Agriculture and Technology, 2-24-16 Nakamachi, Koganei 184-8588, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Smooth isomerization of 4,4,4-trifluorinated propargylic alcohols 1 opened a new and convenient route
Received 25 April 2009
Received in revised form 28 May 2009
Accepted 28 May 2009
to readily get access to the corresponding
presence of Et3N.
a
,b
-unsaturated ketones 4 just by heating a THF solution in the
Ó 2009 Elsevier Ltd. All rights reserved.
Available online 6 June 2009
1. Introduction
HO
HO
Ph Et3Si
+
Ph
Fluorinated materials have been drawing considerable attention
of organic chemists due to their unique characteristics and wide
application to a variety of fields.1 Development of building units
with fluorine-containing groups as well as appropriate function-
alities is considered to be one of the most efficient ways for ready
construction of such useful materials. In this article, we would like
to report our recent results on the interesting conversion of tri-
F3C
F3C
SiEt3
F3C
Pt/C,
Et3SiH,
2
3
OH
Ph
F3C
Et3N
O
Ph
1a
4a
fluorinated propargylic alcohols 1 into the corresponding a,b-un-
saturated carbonyl compounds 4 just by treatment with mild
tertiary amines like triethylamine.
The present isomerization of 1a to 4a was encountered by
chance when the following platinum-catalyzed hydrosilylation of
alkynes was applied2 to our terminally trifluoromethylated prop-
argylic alcohols3 (Scheme 1). Exploration of suitable reaction con-
ditions eventually clarified that neither Pt/C nor Et3SiH was
PDC, Ac2O/CH2Cl2
reflux, 1 h
HO
HO
Ph
Ph
Red-Al/toluene
–78 °C, 3 h
+
F3C
F
F
5a
6a
Scheme 1.
required for the formation of the a,b-unsaturated ketone 4a and it
was Et3N, which actually affected this transformation.4 We have
previously disclosed the synthetic pathway to get access to such
ketones 4 by successive Red-Al reduction and PDC oxidation.5
However, the first step, conversion of the propargylic alcohol 1a to
the corresponding allylic counterpart 5a, was sometimes suffered
from overreduction to the difluorinated homoallylic alcohol 6a
(possibly as the result of SN20 type attack of hydride to the resultant
5a)6 whose separation from the desired 5a was quite troublesome
task. Considering such difficulty, the present process would offer
the significantly convenient direct alternative route to 4 from 1 if
we could find out appropriate conditions for this conversion, which
prompted us to start this study.
2. Results and discussions
First of all, 4,4,4-trifluoro-1-phenylbut-2-yn-1-ol 1a was se-
lected as the representative substrate for finding out the appro-
priate conditions (Table 1). As shown in entry 1, 40 equiv of Et3N
both as a solvent and as a base allowed the complete isomerization
of 1a to furnish 4a in 92% yield after 4 h reflux. Reduction of the
amount of Et3N to 4 equiv affected the reaction only slightly, and
DBU seemed inappropriate due to spontaneous dark colorization of
the solution at the addition as well as detection of a number of
byproduct peaks from the crude mixture by 19F NMR (entries 2 and
3). On the other hand, less basic pyridine did not promote the re-
action at all (entry 4). Different types of solvents were also used in
the presence of 4 equiv of Et3N, and THF was found to be the best
among the solvents tested (entries 5–8), and 4 equiv of Et3N was
appropriate (entries 8 and 10). Slow interconversion from (Z)-4a to
(E)-4a was observed whose energetic preference supposed to lead
* Corresponding author. Tel./fax: þ81 42 388 7038.
E-mail address: tyamazak@cc.tuat.ac.jp (T. Yamazaki).
0040-4020/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2009.05.087

5946
T. Yamazaki et al. / Tetrahedron 65 (2009) 5945–5948
–
to the exclusive production of the latter (entries 8 and 9). On the
basis of these data, treatment of a THF solution of 1 in the presence
of 4 equiv of Et3N at reflux for 8 h has been eventually decided as
the best reaction condition which allowed us to isolate (E)-4a in
94% yield as the sole product.
O
OH
R
Et3N
F3C
F3C
R
+
Et3NH
H
H
1
Int-3
+
Et3N
Et3NH
Table 1
Investigation of the reaction conditionsa
OH
OH
R
O
–
F3C
F3C
•
Ph
OH
Ph
–
Amine/Solvent
reflux
R
F3C
Int-1
F3C
Int-2
1a
4a
+
Et3NH
Entry
Solvent
Amineb
Time (h)
Yield of 4ac (%)
E
c,d (%)
O
O
1
2
3
4
5
6
7
8
d
Et3N (40)
Et3N (4)
DBU (4)
4
4
4
92
77
44
0
88
73
79
68
72
R
Et3N
O
R
H
F3C
(Z)-4
R
H
F3C
d
•
d
F3C
d
Pyridine (4)
Et3N (4)
Et3N (4)
Et3N (4)
Et3N (4)
Et3N (4)
Et3N (1)
d
4
4
2
2
4
8
4
2
d
7
(E)-4
CH2Cl2
Toluene
Hexane
THF
THF
THF
THF
79
91
57
Scheme 2.
38 [24]e
87 (85)f
(94)f
72
78
9
10
11
>99
75
Thus, deprotonation from 1 would furnish two equilibrating an-
ionic species Int-1 and Int-3, and the former intermediate possesses
the allenyl anion resonance structure, Int-2. Reprotonation of Int-2
would lead to the allenol 7,8 which was then converted to a mixture of
0 [89]e
d
a
All reactions were carried out with 1 mmol of the substrate in 5 mL of a solvent
at reflux temperature.
b
In the parenthesis was shown the equivalent of an amine used.
b
-trifluoromethylated
the latter preferred as the kinetically controlled products due to fa-
vorable
pC]O orbital interaction.9 Eventually, slow isomeriza-
a,b-unsaturated ketones (E)- and (Z)-4, usually
c
Determined by 19F NMR unless otherwise noted.
d
Percentage of (E)-4a.
Recovery of the starting material.
Isolated yield.
p
*
–
CF3
e
tion (see entries 1 vs 2 and 3 vs 4 in Table 2) was occurred so as to
afford the sterically less crowded and thus, thermodynamically
preferable (E)-4 by way of reversible 1,4-addition of Et3N, resulting in
isolation of this stereoisomer as the exclusive or the sole products.
The key of this process would be 1) sufficient contribution to acidity
of 1 by an aromatic substituent, and 2) irreversibility of 7 to 1 due to
much lower acidity of the former proton attached to the sp2 carbon
atom of the allenyl framework than the one in the latter at the
propargylic position. Under these conditions, no defluorination was
noticed possibly because of the presence of protons like Et3NHþ as
well as OH in 1 possessing enough acidity to quickly quench the re-
sultant vinylic anion, Int-2.
Preparation of propargylic alcohols 1 as the substrates for the
present reaction was usually initiated by the action of 2 equiv of
LDA to 2-bromo-3,3,3-trifluoropropene, followed by trapping of the
resultant CF3-containing lithium acetylide by appropriate carbonyl
compounds.10 Although this method usually attained excellent
chemical yields for a variety of electrophiles,3b it is empirically
understood that aromatic aldehydes with an electron-withdrawing
moiety were not the substrate of choice: thus, although p-Br–C6H4–
CHO afforded the corresponding propargylic alcohol 1c in 85%
yield,11 a much stronger NO2 moiety at the same position only led to
a complex mixture. Considering that effective activation of the
carbonyl compounds was expected by this substituent, this prob-
lem would stem from the instability of the product 1d and we have
assumed that the strong activation by the p-NO2 group would
render the propargylic proton labile enough to be quickly ab-
stracted by the intermediary alkoxide (for example, Int-3 in
f
Since we have successfully determined suitable reaction condi-
tions for this facile Et3N-mediated transformation from propargylic
alcohols 1 to a,b-unsaturated ketones 4, our interest was turned to
prove scope and limitation of this intriguing process. The results
were summarized in Table 2. All substrates 1 were found to work
well except for 1h with a 2-phenylethyl substituent at the prop-
argylic position, which was intact under these conditions (entry
10).7 Detailed analysis of this data also furnished the information
that an electron-withdrawing moiety on the benzene ring effi-
ciently accelerated the conversion (entries 5 and 6) but retardation
was noticed for substrates with an electron-releasing group (entries
3 and 4). These results allowed us to depict the possible mechanism
for the present transformation as shown in Scheme 2.
Table 2
Isomerization of various propargylic alcohols 1a
O
R
OH
R
Et3N/THF
reflux
F3C
F3C
1
4
Entry
R
Time (h)
Yieldb (%)
E
c (%)
1
2
3
4
5
6
7
8
9
10
Ph–
Ph–
4-MeO–C6H4–
4-MeO–C6H4–
4-Br–C6H4–
4
8
1
12
0.5
0d
9
9
8
85
94
(a)
(a)
(b)
(b)
(c)
(d)
(e)
(f)
78
>99
70
>99
77
74
>99
>99
94
34c
95
>99
95
80
Scheme 2). The isomerized a,b-unsaturated ketones (E)- and (Z)-4d
4-O2N–C6H4–
thus obtained would be sufficiently reactive toward co-existing
nucleophiles by a strongly electron-withdrawing CF3 group to re-
sult in formation of a complex mixture. The experimental result
that p-O2N–C6H4–C(O)CH3 cleanly afforded the desired product 1i
without the propargylic proton in 92% yield (Scheme 3) apparently
supported this idea and anticipated us that in situ capture of the
resultant lithium alkoxide would remove or, at least, reduce
a chance for isomerization to 4d, rendering 1d more easily acces-
sible. Then, brief investigation of appropriate reaction conditions
(E)-PhCH]CH–
1-Naphthyl–
2-Furyl–
90
93
0
(g)
(h)
PhCH2CH2–
8
d
a
All reactions were carried out with 1 mmol of the substrate and 4 mmol of Et3N
in 5 mL of THF at reflux temperature.
b
Isolated yield unless otherwise noted.
c
Percentage of E-4 and yield determined by 19F NMR.
d
Spontaneous reaction at rt was occurred.

T. Yamazaki et al. / Tetrahedron 65 (2009) 5945–5948
5947
1) 2 equiv LDA,
–80 °C, 5 min
3.1.1. 4,4,4-Trifluoro-1-(4-nitrophenyl)but-2-yn-1-ol (1d)
F3C
Br
OH
To a solution of LDA (2.6 mmol) in THF (5 mL) was added
dropwise 2-bromo-3,3,3-trifluoropropene (0.13 mL, 1.3 mmol) at
ꢀ80 ꢁC and after stirring for 5 min at that temperature, a THF so-
lution (2 mL) of tert-butyldimethylsilyl chloride (0.588 g,
3.90 mmol) and 4-nitrobenzaldehyde (0.151 g, 1.00 mmol) was in-
troduced to a reaction mixture. The whole solution was stirred for
10 min at ꢀ80 ꢁC, and the solution was extracted with AcOEt three
times after quenched with satd NH4Cl aq. The organic layer was
dried over MgSO4 and concentrated. 19F NMR for this crude mixture
indicated production of 1d (24%) and 4d as the E,Z mixture (10 and
21%, respectively). The residue was chromatographed on silica gel
to afford 0.049 g (0.200 mmol) of propargylic alcohol,1d. Yield 20%,
Rf¼0.37 (CH2Cl2) or 0.16 (Hexane:CH2Cl2¼1:1). Mp 92 ꢁC. 1H NMR
F3C
O
Me
2)
NO2
O2N
1i 92% yield
–80 °C, 1 h
1) 2 equiv LDA,
OH
+
–80 °C, 5 min
O
F3C
H
2)
O2N
NO2
3 equiv TBDMS,
–80 °C, 10 min
1d 20% yield
d
2.67 (1H, d, J¼5.7 Hz), 5.71 (1H, br s), 7.69–7.74 (2H, m), 8.26–8.33
(2H, m). 13C NMR
d
62.8, 74.0 (q, J¼53.3 Hz), 85.1 (q, J¼6.9 Hz), 113.8
(q, J¼258.0 Hz), 124.1, 127.3, 144.6, 148.1. 19F NMR
d
ꢀ52.07 (s). IR
O
NO2
(KBr)
n 862, 993, 1062, 1132, 1289, 1348, 1516, 1601, 2279, 2879,
3080, 3118, 3452 cmꢀ1. Anal. Calcd for C10H6F3NO3: C, 48.99; H,
2.47; N, 5.71. Found C, 48.99; H, 2.75; N, 5.61.
F3C
4d 31% yield (E:Z=32:68)
Scheme 3.
3.1.2. 4,4,4-Trifluoro-1-(2-furanyl)but-2-yn-1-ol (1g)
To a solution of LDA (2.6 mmol) inTHF (5 mL) was added dropwise
2-bromo-3,3,3-trifluoropropene (0.13 mL, 1.30 mmol) at ꢀ80 ꢁC. Af-
ter stirring for 5 min at that temperature, a THF solution (1 mL) of
furfural (0.096 g, 1.00 mmol) was added and stirring was continued
for 2 h at ꢀ80 ꢁC. Usual work-up and isolation by chromatography
afforded 0.141 g (0.742 mmol) of propargylic alcohol,1g. Yield 74%, bp
clarified that introduction of a mixture of p-O2N–C6H4–CHO and
TBDMSCl was effective for suppression of formation of a variety of
byproducts. Actually, although improvement are still required, this
modification enabled the cleaner reaction to form basically 1d and
4d with the former obtained in 20% yield along with 31% of the
latter in an E:Z ratio of 32:68.12
70 ꢁC (0.4 kPa). 1H NMR
(1H, dd, J¼1.8, 3.3 Hz), 6.49 (1H, d, J¼3.6 Hz), 7.46 (1H, d, J¼1.8 Hz).
d
2.49 (1H, d, J¼7.2 Hz), 5.58 (1H, br s), 6.40
In summary, we have successfully demonstrated the present
isomerization from propargylic alcohols 1 to the corresponding a,b-
13C NMR
d
57.3, 72.2 (q, J¼53.3 Hz), 84.3 (q, J¼6.2 Hz), 108.8, 110.6,
113.9 (q, J¼257.4 Hz), 143.6, 150.2. 19F NMR
d
ꢀ51.61 (s). IR (neat)
n
unsaturated ketones 4, which proceeded simply by refluxing the
THF solution in the presence of Et3N. Success of this process is
highly dependent on the acidity of the propargylic proton in 1 and
because an electron-withdrawing aromatic substituent effectively
activate this proton, isomerization was occurred more smoothly.
Although this method was applicable only to materials with an
aromatic substituent at the propargylic position, advantage of this
process is quite apparent when the tedious previous two-step route
as shown in Scheme 1 was considered.
730, 910, 970,1000,1120,1250,1490, 2200, 3250 cmꢀ1. Anal. Calcd for
C8H5F3O2: C, 50.54; H, 2.65. Found C, 50.64; H, 2.89.
3.1.3. 4,4,4-Trifluoro-1-methyl-1-(4-nitrophenyl)but-2-yn-1-ol (1i)
Yield 92%, Rf¼0.38 (n-hexane:AcOEt¼4:1). 1H NMR
d
1.87 (3H, s),
32.4,
3.37 (1H, br s), 7.74–7.83 (2H, m), 8.24–8.28 (2H, m). 13C NMR
d
69.2, 72.6 (q, J¼53.3 Hz), 85.5 (q, J¼6.2 Hz), 113.9 (q, J¼258.0 Hz),
123.8, 125.8, 147.6, 150.0. 19F NMR
d
ꢀ51.95 (s). IR (neat)
n 856, 1100,
1147, 1277, 1350, 1525, 1604, 2274, 2993, 3423 cmꢀ1. Anal. Calcd
for C11H8F3NO3: C, 50.98; H, 3.11; N, 5.40. Found C, 50.40; H, 3.20;
N, 5.35.
3. Experimental section
3.1. General methods
3.1.4. (E)-4,4,4-Trifluoro-1-phenylbut-2-en-1-one3b (4a)
To a THF (5 mL) solution of 4,4,4-trifluoro-1-phenylbut-2-yn-1-
ol (1a) (0.200 g, 1.00 mmol) was added triethylamine (0.56 mL,
4 mmol) and the mixture was heated at the reflux temperature
under argon atmosphere for 8 h. Addition of 5 mL of 1 M HCl aq and
extraction with ethyl acetate three times furnished an organic layer,
which was dried over anhydrous magnesium sulfate, filtered, and
concentrated in vacuo. The resultant crude material was purified by
column chromatography on silica gel. Yield 94%, Rf¼0.73
Most of reactions where an organic solvent was employed were
performed under argon with magnetic stirring using flame-dried
glassware. Anhydrous THF, Et2O, and CH2Cl2 were purchased and
used without further purification. Unless otherwise noted, mate-
rials were obtained from commercial suppliers and were used
without further purification. Analytical thin-layer chromatography
(TLC) was routinely used for monitoring reactions by generally
using a mixture of n-hexane and ethyl acetate (v/v). Spherical
(Hexane:AcOEt¼4:1). 1H NMR
d
6.83 (1H, qd, J¼8.7, 15.6 Hz), 7.26–
neutral silica gel (63–210
mm or 40–50
mm) was employed for col-
7.57 (3H, m), 7.22 (1H, qd, J¼2.0, 15.5 Hz), 7.96–7.99 (2H, m). 19F
umn chromatography and flush chromatography, respectively. 1H,
13C, and 19F NMR spectra were recorded (1H: 300 MHz; 13C:
75 MHz; 19F: 283 MHz) at room temperature whose data were
NMR
d
ꢀ66.36 (d, J¼6.8 Hz).
3.1.5. (E)-4,4,4-Trifluoro-1-(4-methoxyphenyl)but-2-en-1-one (4b)
Recrystallized from petroleum ether. Yield 95%, Rf¼0.49
reported as follows: chemical shift (
d scale) in parts per million
(ppm) downfield from Me4Si (
d
0.00 for 1H and 13C NMR) or C6F6 (
d
(Hexane:AcOEt¼4:1). Mp 36 ꢁC. 1H NMR
d 3.90 (s, 3H), 6.80 (1H, qd,
J¼6.8, 15.6 Hz), 6.99 (2H, d, J¼8.4 Hz), 7.54 (1H, qd, J¼1.8, 16.5 Hz),
ꢀ162.2) used as internal standards, number of protons or fluorines,
multiplicity (singlet, s; doublet, d; triplet, t; quartet, q; multiplet,
m; broad peak, br; etc.), and coupling constant (J in Hz). Infrared
(IR) spectra were reported in wave number (cmꢀ1).
7.98 (2H, d, J¼8.7 Hz). 13C NMR
d
55.4, 114.1, 122.7 (q, J¼269.8 Hz),
129.0,129.3 (q, J¼34.7 Hz),131.0 (q, J¼5.6 Hz),131.2,164.4,185.9. 19F
NMR
d
ꢀ66.26 (d, J¼4.5 Hz). IR (KBr)
n 650, 830, 970, 1030, 1130,
Substrates 1a,3b 1b–1c,11 1e,3b 1f,11 and 1h3b were prepared as
described in the literature.
1180, 1260, 1310, 1420, 1450, 1520, 1590, 1640, 1670, 2950 cmꢀ1
Anal. Calcd for C11H9F3O2: C, 57.40; H, 3.94. Found C, 57.41; H, 3.94.
.

5948
T. Yamazaki et al. / Tetrahedron 65 (2009) 5945–5948
3.1.6. 1-(4-Bromophenyl)-4,4,4-trifluorobut-2-en-1-one (4c)
3.1.10. (E)-4,4,4-Trifluoro-1-(2-furanyl)but-2-en-1-one14 (4h)
Yield quant, IR (KBr)
n
651, 729, 907, 1008, 1142, 1274, 1297, 1306,
Yield 93%, Rf¼0.68 (Hexane:AcOEt¼4:1). 1H NMR
d 6.62 (1H, dd,
1390, 1472, 1587, 1687, 2253 cmꢀ1. Anal. Calcd for C8H5F3O2: C,
50.54; H, 2.65. Found C, 50.64; H, 2.89.
J¼1.7, 3.5 Hz), 6.85 (1H, qd, J¼6.6, 15.6 Hz), 7.36 (1H, dd, J¼0.8,
3.6 Hz), 7.39 (1H, qd, J¼2.3, 15.6 Hz), 7.71 (1H, dd, J¼0.8, 1.6 Hz). 19F
NMR
d
ꢀ66.33 (d, J¼6.8 Hz).
3.1.6.1. (E)-Isomer. Rf¼0.78 (Hexane:AcOEt¼4:1). Mp 51–52 ꢁC. 1H
NMR
d
6.84 (1H, qd, J¼6.6, 15.6 Hz), 7.49 (1H, qd, J¼2.1, 15.6 Hz),
Acknowledgements
7.68 (2H, m), 7.85 (2H, m). 13C NMR
d
122.4 (q, J¼270.0 Hz), 130.1,
130.4 (q, J¼5.6 Hz), 130.6 (q, J¼34.7 Hz), 132.3, 134.8, 186.8. 19F NMR
The generous gift of 2-bromo-3,3,3-trifluoropropene by F-Tech,
Inc. is greatly acknowledged.
(CDCl3)
d
ꢀ62.09 (d, J¼6.8 Hz).
3.1.6.2. (Z)-Isomer. Rf¼0.47 (Hexane:AcOEt¼4:1). 1H NMR
d 6.11
(1H, qd, J¼4.8, 12.9 Hz), 6.82 (1H, d, J¼12.6 Hz), 7.65 (2H, m), 7.79
References and notes
(2H, m). 19F NMR (CDCl3)
d
ꢀ62.12 (d, J¼9.3 Hz).
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New York, NY, 2009; (b) Uneyama, K. Organofluorine Chemistry; Blackwell:
Oxford, 2006.
3.1.7. 4,4,4-Trifluoro-1-(4-nitrophenyl)but-2-en-1-one (4d)
Yield 95%, IR (neat)
n 648, 716, 723, 908, 1144, 1275, 1289, 1310,
2. Chauhan, M.; Hauck, B. J.; Keller, L. P.; Boudjouk, P. J. Organomet. Chem. 2002,
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1996, 80, 145–147.
4. It has been reported that Sonogashira coupling reactions with propargylic al-
cohols promoted this type of transformation. See, for example: (a) Mu¨ ller, T. J.
J.; Ansorge, M.; Aktah, D. Angew. Chem., Int. Ed. 2000, 39, 1253–1256; (b) Coelho,
A.; Sotelo, E.; Ravin˜a, E. Tetrahedron 2003, 59, 2477–2484; See also: Sonye, J. P.;
Koide, K. Org. Lett. 2006, 8, 199–202.
5. Yamazaki, T.; Ichige, T.; Kitazume, T. Org. Lett. 2004, 6, 4073–4076.
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2027–2035.
7. Peaks of a CF3 group were observed in the same area as the other 4 after
reaction in the presence of a Wilkinson catalyst, but no further investigation
was tried because of only a moderate level of conversion as well as low product
selectivity. See: Saı¨ah, M. K. E.; Pellicciari, R. Tetrahedron Lett. 1995, 36,
4497–4500.
8. THP-protected allenol was in fact isolated by triton-B-mediated isomerization
of THP ether of propargyl alcohol Ishikawa, T.; Mizuta, T.; Hagiwara, K.; Aikawa,
T.; Kudo, T.; Saito, S. J. Org. Chem. 2003, 68, 3702–3705.
9. (a) Bumgardner, C. L.; Bunch, J. E.; Whangbo, M.-H. Tetrahedron Lett. 1986, 27,
1883–1886; (b) Bumgardner, C. L.; Bunch, J. E.; Whangbo, M.-H. J. Org. Chem.
1986, 51, 4082–4083.
10. As an alternative route, it was reported that addition of 3 equiv of BuLi to HFC-
245fa (CF3CH2CHF2) also furnished the same lithium acetylide. See: Brisdon, A.
K.; Crossley, I. R. Chem. Commun. 2002, 2420–2421.
1388, 1532, 1653, 1687, 2257 cmꢀ1. Anal. Calcd for C10H6F3NO3: C,
48.99; H, 2.47; N, 5.71. Found C, 49.27; H, 2.60; N, 5.59.
3.1.7.1. (E)-Isomer. Rf¼0.63 (Hexane:AcOEt¼4:1). 1H NMR
d 6.90
(1H, qd, J¼6.6, 15.3 Hz), 7.53 (1H, qd, J¼2.1, 15.6 Hz), 8.15 (2H, m),
8.39 (2H, m). 13C NMR
d
122.2 (q, J¼270.0 Hz), 124.1, 129.8, 130.2 (q,
J¼5.6 Hz), 131.7 (q, J¼35.4 Hz), 140.5, 150.7, 186.7. 19F NMR
(d, J¼6.8 Hz).
d
ꢀ66.55
3.1.7.2. (Z)-Isomer. Rf¼0.33 (Hexane:AcOEt¼4:1). 1H NMR
d 6.21
(1H, qd, J¼7.8, 12.6 Hz), 6.88 (1H, d, J¼12.6 Hz), 8.10 (2H, m), 8.37
(2H, m). 19F NMR (CDCl3)
d
ꢀ62.05 (d, J¼6.8 Hz).
3.1.8. (1E,4E)-6,6,6-Trifluoro-1-phenylhexa-1,4-dien-3-one13 (4e)
Yield 80%, Rf¼0.65 (Hexane:AcOEt¼4:1). 1H NMR (CDCl3)
d 6.76
(1H, qd, J¼6.6, 15.3 Hz), 6.95 (1H, d, J¼16.2 Hz), 7.13 (1H, qd, J¼1.8,
15.6 Hz), 7.44–7.46 (3H, m), 7.60–7.62 (2H, m), 7.73 (1H, d,
J¼15.9 Hz). 19F NMR (CDCl3)
d
ꢀ66.34 (d, J¼6.8 Hz).
3.1.9. (E)-4,4,4-Trifluoro-1-(1-naphthyl)but-2-en-1-one (4f)
Yield 90%, Rf¼0.70 (Hexane:AcOEt¼4:1). 1H NMR
d 6.76 (1H, qd,
J¼6.6, 15.6 Hz), 7.42 (1H, qd, J¼2.1, 15.6 Hz), 7.53–7.67 (4H, m), 7.86
11. Yamazaki, T.; Yamamoto, T.; Ichihara, R. J. Org. Chem. 2006, 71, 6251–6253.
12. Previously, the same isomerization of 1a to (E)-4a was reported to be oc-
curred in the presence of Na2CO3, LiCl, and a catalytic amount of Pd(OAc)2 in
a DMF solvent at 100 ꢁC (72% yield), while on the basis of our result, this
reaction would proceed only by the action of Na2CO3. See: Jiang, Z.-X.; Qing,
F.-L. J. Fluorine Chem. 2003, 123, 57–60.
13. (a) Pashkevich, K. I.; Khomutov, O. G. Izv. Akad. Nauk, Ser. Khim. 1996, 2285–
2287; (b) Ates, C.; Janouse, Z.; Viehe, H. G. Tetrahedron Lett. 1993, 34, 5711–5714.
14. Christophe, C.; Billard, T.; Langlois, B. R. Eur. J. Org. Chem. 2005, 3745–3748.
(1H, dd, J¼1.1, 7.4 Hz), 7.93 (1H, dd, J¼1.8, 7.5 Hz), 8.54 (1H, d,
J¼8.4 Hz). 13C NMR
d
122.6 (q, J¼266.2 Hz), 124.2, 125.4, 126.8,
128.3, 128.6, 129.2, 130.0 (q, J¼35.3 Hz), 130.3, 133.8, 133.8, 133.9,
134.7 (q, J¼5.6 Hz), 191.2. 19F NMR
d
ꢀ66.24 (d, J¼6.8 Hz). IR (neat)
n
650, 800, 830, 990, 1150, 1280, 1300, 1320, 1530, 1600, 1660,
3150 cmꢀ1. Anal. Calcd for C14H9F3O: C, 67.20; H, 3.63. Found C,
67.02; H, 3.78.