Facile one-pot preparation of allylic alcohols with a fluorine-containing alkyl group at the γ-position

Article abstract of DOI:10.1016/j.jfluchem.2013.07.016

A useful one-pot preparation method of allylic alcohols with fluorinated alkyl groups at the γ position was developed from the corresponding enoates by way of the DIBAL-mediated half reduction, followed by nucleophilic attack of Grignard reagents to aldehydes equilibrating with aluminium acetals.

Full text of DOI:10.1016/j.jfluchem.2013.07.016

Journal of Fluorine Chemistry 155 (2013) 151–154
Contents lists available at ScienceDirect
Journal of Fluorine Chemistry
journal homepage: www.elsevier.com/locate/fluor
Facile one-pot preparation of allylic alcohols with a
fluorine-containing alkyl group at the g-position
*
Takashi Yamazaki , Masashi Ichikawa, Tomoko Kawasaki-Takasuka, Shigeyuki Yamada
Division 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:
A useful one-pot preparation method of allylic alcohols with fluorinated alkyl groups at the
g position
Received 16 March 2013
Accepted 25 July 2013
Available online 20 August 2013
was developed from the corresponding enoates by way of the DIBAL-mediated half reduction, followed
by nucleophilic attack of Grignard reagents to aldehydes equilibrating with aluminium acetals.
ß 2013 Elsevier B.V. All rights reserved.
Keywords:
Aluminium acetals
a,b-Unsaturated esters
Perfluoroalkyl groups
Allylic alcohols
1. Introduction
2. Results and discussion
In the field of synthetic chemistry, allylic alcohols have been
regarded as one of the most important class of compounds and
widely employed as versatile substrates for Claisen rearrangement
[1], Sharpless epoxidation [2], Diels–Alder reactions [3], and so
forth [4]. This is also the case for fluorine-containing counterparts,
and for example, redox isomerization [5], palladium-catalyzed SN20
reactions [6], osmium-catalyzed diol formation [7] have been
Our fundamental concept was based on the consideration that
the intermediary aluminium acetal Int-A obtained by the DIBAL
reduction of enoates 1 at ꢀ80 8C would afford, with release of an
aluminium alkoxide molecule, the corresponding aldehydes 3
which would be then conveniently trapped in situ by such
representative nucleophiles like Grignard or lithium reagents
(Scheme 1) [11]. This method should be superior to the previously
reported procedure due to no requirement of isolation of reactive
and tough-to-handle intermediary aldehydes 3 [12]. Following to
this scheme, a small excess amount of DIBAL (1.1 equiv.) was
subjected to a THF solution containing benzyl (E)-4,4,4-trifluor-
obut-2-enoate 1aa at ꢀ80 8C, and the whole mixture was stirred
for 1 h at the same temperature. At this point, disappearance of the
substrate 1aa was noticed by TLC analysis with observation of the
resultant benzyl alcohol, which was the clear proof of complete
consumption of 1aa and formation of Int-A. To this flask was added
PhMgBr, and the reaction was continued further 1 h with keeping
the temperature at ꢀ80 8C, but this protocol afforded only a small
amount of the desired product 4aa (Table 1, entry 1). Increase of
the amount of the Grignard reagent to 1.5 equiv. did not affect the
outcome at all (entry 2), and only a complex mixture was formed
by raising the reaction temperature from ꢀ80 to 0 8C after addition
of PhMgBr (entry 3). However, alteration of the solvent from THF to
Et2O apparently affected the present system and 1.5 equiv. loading
of PhMgBr led to isolation of 4aa in 59% yield, but unfortunately
with low reproducibility (entry 6). Interesting to note was the
deteriorating effect of THF, leading to failure of the reaction even in
published in this decade starting from allylic alcohols with a g-CF3
substituent [8]. In our hand, because of ready availability of 4,4,4-
trifluorobut-2-enoates by way of Horner–Wadsworth–Emmons
reactions using such commercially available aldehyde equivalents
as trifluoroacetaldehyde hydrate or hemiacetals [9], our initial plan
to construct such allylic alcohols were to synthesize
a,b-
unsaturated ketones by nucleophilic 1,2-addition of appropriate
Grignard reagents at low temperature [10], followed by NaBH4
reduction, but this route was found not to give any fruitful results.
Then we have started our investigation to develop a new and
efficient pathway to get access to the title compounds from
fluorinated enoates as substrates, whose results are reported
below.
*
Corresponding author. Tel.: +81 42 388 7038; fax: +81 42 388 7038.
E-mail address: tyamazak@cc.tuat.ac.jp (T. Yamazaki).
0022-1139/$ – see front matter ß 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jfluchem.2013.07.016

152
T. Yamazaki et al. / Journal of Fluorine Chemistry 155 (2013) 151–154
Table 1
O
O
PhMgBr
Investigation of reaction conditions
F3C
OR
F3C
Ph
1) DIBAL (1.1 equiv),
OH
Ph
C, 1 h
CO2Bn
1aa (R=Bn)
1ab (R=Et)
2aa
F3C
F3C
2) PhMgBr, Temp., 1 h
1ab
4aa
DIBAL,
–80 °C
Entry
Solvent
PhMgBr (equiv.)
Temp. (8C)
Yield of 4aaa (%)
–i-Bu2Al-OR
OAl-i-Bu2
OR
O
1
2
THF
1.1
1.5
1.1
1.1
1.1
1.5
2.0
3.0
1.5
1.5
1.5
ꢀ80
ꢀ80
(5)
THF
(5)
3
THF
ꢀ80 to 0
ꢀ80
Complex
Trace
(14)
H
F3C
F3C
4b
5
Et2O
Et2O
Et2O
Et2O
Et2O
Et2O
Et2O
Et2O
H
3a
ꢀ80
Int-A
6
ꢀ80
59 (66)
(12)
7
ꢀ80
1) PhMgBr
2) H3O+
8
ꢀ80
(17)
9
ꢀ80 to 0
ꢀ80 to rt
ꢀ80 to rt
56 (59)
60 (64)
72
10
11c
OH
Ph
Isolated yields, and in the parenthesis were shown the yields determined by 19
F
a
NMR.
F3C
b
PhMgBr prepared in THF was used.
c
The corresponding ethyl ester 1aa was employed as the substrate.
4aa
Scheme 1.
an Et2O solvent as long as the Grignard reagent was prepared in
THF (entry 4). Further increase of the quantity of this nucleophile
was ineffective and the yields decreased significantly. Warming up
the reaction mixture either to 0 8C or rt after addition of PhMgBr at
ꢀ80 8C resulted in better consequence, and the desired allylic
alcohol 4aa was isolated in an acceptable level of 56 and 60% yields
(entries 9 and 10, respectively). Because of easy preparation and
handling in terms of its boiling point, the benzyl ester 1ab was used
as the starting material, while the resultant benzyl alcohol was
found to cause troublesome situation at the chromatographic
isolation step due to its close polarity to the product 4aa.
Eventually, this problem was solved by employment of the
corresponding ethyl ester 1ab, and this protocol in 10 mmol scale
was found to attain 72% isolated yield.
affording a complex mixture (entry 2). This would be understood
on the basis of the instability of the corresponding intermediary
aluminium acetal, smoothly giving crotonaldehyde which would
further reacted with PhMgBr. On the other hand, the present
protocol was applicable to other fluorine-containing enoates 1ba
to 1ea, allowing to construct the corresponding allylic alcohols 4ba
to 4ea in good to excellent yields (entries 3–6). However, switch of
the nucleophile from PhMgBr to PhCH2CH2MgBr gave the
disappointing result (entry 7), but the low yield of 4ab was nicely
improved to an acceptable level just by alteration of the solvent
from Et2O to CH2Cl2 which attained 51% isolated yield (entry 8).
This nucleophile was also subjected to a solution of enoates 1da
and 1ea with C2F5 as well as C6F13 groups, respectively, and the
desired product was obtained in good yield in the case of 1 da
(entry 10), while only 26% yield was recorded by 1ea probably due
to lower solubility of this substrate in CH2Cl2 (entry 11). Steric
bulkiness of nucleophiles seemed to affect the reaction severely,
and 26% yield was obtained by the action of c-C6H11MgBr (entry 9).
At the next stage, optimized reaction conditions thus deter-
mined were applied to a variety of
a,b-unsaturated esters 1
(Table 2). As described in entry 11 in Table 1, trifluorinated
a,b-
unsaturated ester 1aa afforded 4aa in 72% yield, which was in
sharp contrast to the case of non-fluorinated crotonate 1fa, only
3. Conclusion
Table 2
Reactions of various enoates 1 with Grignard reagents
As mentioned above, we have successfully developed a useful
one-pot preparation method of allylic alcohols 4 with fluorinated
1) DIBAL (1.1 equiv),
OH
Et2O
C, 1 h
CO2Et
alkyl groups at the
g position, starting from the corresponding
Rf
Rf
R
2) RMgBr (1.1 equiv),
C to rt, 1 h
fluorinated -unsaturated esters 1 by way of the DIBAL-
a,b
1
4
mediated half reduction, followed by nucleophilic attack of
Grignard reagents to aldehydes equilibrating with aluminium
acetals. Further improvement of this method is in progress in this
laboratory.
Entry
Rf
R
Product
Yielda (%)
1
2
CF3 (1aa)
CH3 (1fa)
CHF2 (1ba)
CClF2 (1ca)
C2F5 (1da)
C6F13 (1ea)
CF3 (1aa)
CF3 (1aa)
CF3 (1aa)
C2F5 (1da)
C6F13 (1ea)
Phꢀ
4aa
–
72
Ph–
Complex
62
4. Experimental
3
Ph–
4ba
4ca
4da
4ea
4ab
4ab
4ac
4db
4eb
4
Ph–
85
5
Ph–
81
4.1. General
6
Ph–
89
7
PhCH2CH2–
PhCH2CH2–
17
All reactions were carried out under an atmosphere of argon in
dried glassware with magnetic stirring. Anhydrous Et2O, THF and
CH2Cl2 were purchased and were used without further purifica-
tion. Analytical thin-layer chromatography (TLC) was routinely
used for monitoring reactions by generally using a mixture of
8b
9b
10b
11b
51
c-C6H11
–
26
PhCH2CH2–
PhCH2CH2–
58
26
a
Isolated yields.
b
CH2Cl2 was used as a solvent instead of Et2O.
hexane and AcOEt (v/v). Spherical neutral silica gel (63–210
mm)

T. Yamazaki et al. / Journal of Fluorine Chemistry 155 (2013) 151–154
153
was employed for column chromatography. 1H (300.40 MHz), 13
C
700 cmꢀ1. Anal. Calcd for C10H9ClF2O: C,54.94; H, 4.15. Found C,
54.85; H, 4.17.
(75.45 Hz), and 19F (282.65 Hz) NMR spectra were recorded on a
JEOL AL 300 spectrometer in CDCl3 and chemical shifts were
recorded in parts per million (ppm), downfield from internal
4.2.6. (E)-4,4,5,5,5-Pentafluoro-1-phenylpent-2-en-1-ol ((E)-4 da)
tetramethylsilane (Me4Si:
d
0.00, for 1H and 13C) or hexafluor-
Yield 81%, Rf = 0.54 (hexane:AcOEt = 3:1). 1H NMR
d
2.09 (1H, d,
J = 3.6 Hz), 5.37 (1H, q, J = 13.3 Hz), 6.07 (1H, d, J = 15.6 Hz), 6.57
(1H, ddt, J = 15.6, 4.2, 2.2 Hz), 7.12–7.38 (5H, m). 13C NMR
72.9,
obenzene (C6F6:
d
ꢀ163.00 for 19F). Data were tabulated in the
following order: number of protons, multiplicity (s, singlet; d,
doublet; t, triplet; q, quartet; quint, quintet; sex, sextet; m,
multiplet; b, broad peak), coupling constants in Hertz. Infrared (IR)
spectra were obtained on a JASCO A-302 spectrometer and
reported in wave numbers (cmꢀ1).
d
112.4 (tq, J = 249.3, 38.5 Hz), 116.0 (t, J = 23.5 Hz), 119.2 (qt,
J = 284.7, 37.8 Hz), 126.7, 128.7, 129.0, 140.3, 143.2 (t, J = 8.1 Hz).
19F NMR
d
ꢀ116.72 (2F, d, J = 11.4 Hz), ꢀ86.46 (3F, s). IR
n (neat)
3360, 2360, 2341, 1683, 1342, 1203, 1039, 979, 764, 700 cmꢀ1
.
Anal. Calcd for C11H9F5O: C, 52.39; H, 3.60. Found C, 52.42; H, 3.53.
4.2. General procedure for the preparation of 4
4.2.7. (E)-6,6,7,7,7-Pentafluoro-1-phenylhept-4-en-3-ol ((E)-4db)
4.2.1. (E)-4,4,4-Trifluoro-1-phenylbut-2-en-1-ol ((E)-4aa) [13]
To a solution of ethyl (E)-4,4,4-trifluorobut-2-enoate 1aa
1.690 g (10.1 mmol) in Et2O (20 mL) was added a hexane solution
(1.02 M) of DIBAL 10.3 mL (10.5 mmol) at ꢀ80 8C and after 1 h
stirring at that temperature, PhMgBr 12.0 mL (1.21 M in Et2O,
14.5 mmol) was added. The whole mixture was stirred at ꢀ80 8C
for 15 min, then rt for 1 h where 1 M HCl (15 mL) was added.
Extraction with Et2O three times, and the obtained organic layer
was dried over anhydrous MgSO4. Filtration and evaporation of the
volatiles furnished oily materials which was chromatographed on
silica gel (hexane:AcOEt = 4:1) to afford 1.463 g (7.24 mmol) of (E)-
4,4,4-trifluoro-1-phenylbut-2-en-1-ol (E)-4aa as a colourless oil in
CH2Cl2 was employed as a solvent instead of Et2O. Yield 45%,
Rf = 0.32 (hexane:AcOEt = 4:1). 1H NMR
d
1.71 (1H, d, J = 4.8 Hz),
1.91 (2H, m), 2.76 (2H, m), 4.33 (1H, m), 5.90 (1H, dt, J = 15.3,
12.0 Hz), 6.47 (1H, ddt, J = 15.3, 4.5, 2.4 Hz), 7.19–7.33 (5H, m). 13
NMR 31.3, 37.9, 69.8, 112.3 (tq, J = 250.0, 38.5 Hz), 116.2 (t,
J = 23.5 Hz), 118.9 (qt, J = 285.4, 37.8 Hz), 126.5, 128.4, 128.6,
140.9, 144.4 (t, J = 8.1 Hz). 19F NMR
–116.73 (2F, d, J = 13.8 Hz), –
C
d
d
86.56 (3F, s). Anal. Calcd for C13H13F5O: C, 55.72; H, 4.68. Found C,
55.82; H, 4.70.
4.2.8. (E)-4,4,5,5,6,6,7,7,8,8,9,9,9-Tridecafluoro-1-phenylnon-2-en-
1-ol ((E)-4ea)
72% yield. Rf = 0.41 (hexane:AcOEt = 4:1). 1H NMR
d
2.09 (1H, dd,
Yield 89%, Rf = 0.49 (hexane:AcOEt = 3:1). 1H NMR
d
1.62 (1H,
bs), 5.39 (1H, m), 6.10 (1H, dt, J = 15.8, 10.2 Hz), 6.56 (1H, ddt,
J = 15.8, 4.2, 2.2 Hz), 7.30–7.43 (5H, m). 13C NMR
73.1, 116.3 (t,
J = 23.5 Hz), 126.6, 128.7, 129.0, 140.4, 143.2 (t, J = 8.7 Hz). 19F NMR
ꢀ127.41 (2F, m), ꢀ124.55 (2F, m), ꢀ124.14 (2F, brs), ꢀ122.88 (2F,
brs), ꢀ112.90 (2F, quint, J = 15.0 Hz), ꢀ82.1 (3F, t, J = 10.3 Hz). IR
(neat) 3351, 2360, 2342, 1683, 1240, 1202, 1145, 980, 700 cmꢀ1
J = 3.9, 0.6 Hz), 5.34 (1H, m), 6.05 (1H, dqd, J = 15.5, 6.6, 2.0 Hz),
6.53 (1H, ddq, J = 15.6, 3.7, 1.5 Hz), 7.28–7.44 (5H, m). 19F NMR
ꢀ65.28 (d, J = 6.0 Hz).
d
d
d
4.2.2. (E)-6,6,6-Trifluoro-1-phenylhex-4-en-3-ol ((E)-4ab) [8b]
n
.
CH2Cl2 was employed as a solvent instead of Et2O. Yield 51%,
Rf = 0.44 (hexane:AcOEt = 4:1). 1H NMR
1.67 (1H, d, J = 4.8 Hz),
1.90 (2H, m), 2.76 (2H, m), 4.29 (1H, m), 5.90 (1H, dqd, J = 15.6, 6.6,
1.8 Hz), 6.42 (1H, ddq, J = 15.6, 4.2, 2.1 Hz), 7.14–7.33 (5H, m). 13
d
Anal. Calcd for C15H9F13O: C, 39.84; H, 2.01. Found C, 39.82; H, 2.01.
C
4.2.9. (E)-6,6,7,7,8,8,9,9,10,10,11,11,11-Tridecafluoro-1-
phenylundec-4-en-3-ol ((E)-4eb)
NMR d 31.2, 37.7, 69.4, 117.8 (q, J = 34.1 Hz), 123.1 (q, J = 268.6 Hz),
126.1, 128.3, 128.5, 141.0, 142.1 (q, J = 6.2 Hz). 19F NMR
(d, J = 6.9 Hz).
d
ꢀ65.36
CH2Cl2 was employed as a solvent instead of Et2O. Yield 26%,
Rf = 0.38 (hexane:AcOEt = 4:1). 1H NMR
d
1.70 (1H, d, J = 4.8 Hz),
1.91 (2H, m), 2.76 (2H, m), 4.35 (1H, br), 5.93 (1H, dt, J = 15.3,
12.9 Hz), 6.46 (1H, ddt, J = 15.3, 4.2, 2.4 Hz), 7.19–7.33 (5H, m). 13
NMR 31.3, 38.0, 69.9, 116.5 (t, J = 23.5 Hz), 126.2, 128.4, 128.6,
140.9, 144.5 (t, J = 8.0 Hz). 19F NMR
ꢀ127.46 (2F, m), ꢀ124.70 (2F,
m), ꢀ124.21 (2F, m), ꢀ122.92 (2F, m), ꢀ112.85 (q, J = 13.8 Hz),
4.2.3. (E)-1-Cyclohexyl-4,4,4-trifluorobut-2-en-1-ol ((E)-4ac) [14]
C
CH2Cl2 was employed as a solvent instead of Et2O. Yield 26%,
d
Rf = 0.43 (hexane:AcOEt = 4:1). 1H NMR
d
1.00–1.27 (5H, m), 1.46–
d
1.50 (1H, m), 1.60 (1H, d, J = 4.8 Hz), 1.61–1.80 (5H, m), 4.06 (1H,
m), 5.88 (1H, dqd, J = 15.8, 6.4, 1.8 Hz), 6.41 (1H, ddq, 15.8, 5.0,
ꢀ82.07 (3F, t, J = 9.0 Hz). IR
n (neat) 3368, 2931, 2349, 1675, 1364,
2.0 Hz). 13C NMR
d
25.9, 26.0, 26.2, 27.8, 28.7, 43.4, 74.7, 118.5 (q,
1240, 1203, 1145, 700 cmꢀ1. Anal. Calcd for C17H13F13O: C, 42.51;
H, 2.73. Found C, 42.68; H, 2.65.
J = 33.6 Hz), 123.2 (q, J = 268.5 Hz), 141.1 (q, J = 6.2 Hz). 19F NMR
ꢀ65.15 (d, J = 6.8 Hz).
d
References
4.2.4. (E)-4,4-Difluoro-1-phenylbut-2-en-1-ol ((E)-4ba)
Yield 62%, Rf = 0.17 (hexane:AcOEt = 4:1). 1H NMR
d
2.10 (1H,
bs), 5.31 (1H, m), 6.00 (1H, m), 6.12 (1H, m), 6.25 (1H, ddt, J = 15.6,
4.5, 3.3 Hz), 7.26–7.41 (5H, m). 13C NMR
73.2, 114.5 (t,
J = 234.5 Hz), 122.6 (t, J = 24.2 Hz), 125.4, 126.4, 128.3, 128.5,
128.8, 140.2 (t, J = 11.2 Hz), 141.1. 19F NMR
ꢀ112.47 (1F, m),
(neat) 3360, 3032, 2881, 2327, 1737, 1682,
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d
d
ꢀ112.67 (1F, m). IR
n
1494, 1455, 1387, 1295, 1143, 1019, 972, 764, 701 cmꢀ1. Anal.
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Yield 85%, Rf = 0.56 (hexane:AcOEt = 5:1). 1H NMR
d
2.06 (1H, d,
J = 3.9 Hz), 5.35 (1H, m), 6.22 (1H, dtd, J = 15.6, 8.7, 1.5 Hz), 6.42
(1H, ddt, J = 15.6, 4.2, 2.1 Hz), 7.32–7.42 (5H, m). 13C NMR
72.7,
123.9 (t, J = 27.2 Hz), 125.0 (t, J = 286.3 Hz), 126.6, 128.6, 129.0,
138.0 (t, J = 6.8 Hz), 140.6. 19F NMR
ꢀ51.44 (d, J = 9.3 Hz). IR
(neat) 3350, 2360, 2341, 1674, 1494, 1456, 1233, 1069, 964, 764,
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d
n
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154
T. Yamazaki et al. / Journal of Fluorine Chemistry 155 (2013) 151–154
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