Mechanistic study on a unique SN2′-type reaction of allylic alcohols with organolithium reagent accelerated by a proximal trifluoromethyl group

Article abstract of DOI:10.1016/j.jfluchem.2015.07.024

We previously found that treatment of (Z)-trifluoromethylated-2-aryl allylic alcohols with organolithium provided the S_N2′-type product through C-O bond cleavage. Interestingly, no additive was required to enhance the nucleophilicity of the organolithium, and the free hydroxyl group served as a leaving group. The mechanistic studies of the unique transformation indicated that chelation of alkoxide and fluorine of the trifluoromethyl group to the lithium ion play a crucial role in controlling the reactivity and selectivity. Furthermore, theoretical investigation supported this interpretation.

Full text of DOI:10.1016/j.jfluchem.2015.07.024

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Contents lists available at ScienceDirect
Journal of Fluorine Chemistry
journal homepage: www.elsevier.com/locate/fluor
Mechanistic study on a unique SN20-type reaction of allylic alcohols
with organolithium reagent accelerated by a proximal trifluoromethyl
group
Hiromichi Egami a,b,e, Yoshihiko Usui a,c, Shintaro Kawamura a,b,d, Ryo Shimizu a,c
,
Sayoko Nagashima c, Mikiko Sodeoka a,b,c,d,
*
a Synthetic Organic Chemistry Laboratory, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
b Sodeoka Live Cell Chemistry Project, ERATO, Japan Science and Technology Agency, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
c Graduate School of Science and Engineering, Saitama University, 255 Shimo-okubo, Sakura-ku, Saitama 338-8570, Japan
d RIKEN Center for Sustainable Resource Science, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
e School of Pharmaceutical Sciences, University of Shizuoka, 52-1 Yada, Suruga-ku, Shizuoka 422-8526, Japan
A R T I C L E I N F O
A B S T R A C T
Article history:
We previously found that treatment of (Z)-trifluoromethylated-2-aryl allylic alcohols with organo-
lithium provided the SN20-type product through C–O bond cleavage. Interestingly, no additive was
required to enhance the nucleophilicity of the organolithium, and the free hydroxyl group served as a
leaving group. The mechanistic studies of the unique transformation indicated that chelation of alkoxide
and fluorine of the trifluoromethyl group to the lithium ion play a crucial role in controlling the reactivity
and selectivity. Furthermore, theoretical investigation supported this interpretation.
ß 2015 Elsevier B.V. All rights reserved.
Received 23 April 2015
Received in revised form 22 July 2015
Accepted 22 July 2015
Available online xxx
Dedicated to Dr. Veronique Gouverneur on
the occasion of her receipt of the ACS Award
for Creative Work in Fluorine Chemistry
2015.
Keywords:
Trifluoromethyl
Organolithium reagent
Proximal effect
Allylic alcohol
1. Introduction
On the other hand, addition of an organolithium reagent to
alkenes is a well-established reaction known as carbolithiation
The SN20 reaction is
a
fundamental reaction in organic
[3]. Additives such as N,N,N0,N0-tetramethylethylenediamine
(TMEDA), N,N0-dimethylpropyleneurea (DMPU), or a directing
group that has a strong coordination ability to the lithium ion are
usually required to promote this reaction, except in the case of tert-
butyllithium [4]. Despite extensive studies on the carbolithiation
of alkenes, including allylic alcohols [5], very few examples of SN20-
type reaction of allylic alcohols are known [6]. Reported examples
are restricted to terminal alkene or cyclopent-2-en-1-ol, and
TMEDA is required as an additive to enhance the nucleophilicity of
the organolithium reagents by dissociating their aggregated state.
There is increasinginterestinintroducingatrifluoromethylgroup
into organic frameworks due to its metabolic stability, lipophilicity
and electronic character [7], and trifluoromethylation reactions, as
well as transformations of trifluoromethylated compounds, have
beenactivelystudied[8].Sincecarbolithiationexploitstheproperties
of the trifluoromethyl group, trifluoromethyl-substituted alkene
chemistry, and various types of SN20 reactions have long been
utilized in organic synthesis. In general, an allylic compound
bearing a leaving group, such as halide or sulfonate, is used as an
electrophile in SN20 reactions with soft nucleophiles, and transition
metal catalysis has recently enabled the use of allylic carboxylates
and allylic alcohols in this type of reaction [1]. However, the SN20
reaction of allylic alcohol with a main group metal reagent, such as
organolithium, is difficult without prior activation of the hydroxyl
group [2].
*
Corresponding author at: Synthetic Organic Chemistry Laboratory, RIKEN, 2-1
Hirosawa, Wako, Saitama 351-0198, Japan.
E-mail address: sodeoka@riken.jp (M. Sodeoka).
http://dx.doi.org/10.1016/j.jfluchem.2015.07.024
0022-1139/ß 2015 Elsevier B.V. All rights reserved.
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(a)
species, such as
a-trifluoromethylstyrene, have been investigated as
substrates [9]. But, in these cases, the alkyl anion attacks the
position of the trifluoromethyl group and gem-difluoroalkene is
generated via elimination of the fluoride ion.
b
-
OH
CH3
n-BuLi (5 equiv.)
CH3
n-Bu
5: 3%
+
4: 86%
Ph
Ph
n-hexane, 23 °C, 3 h
Ph
We have been investigating trifluoromethylation reactions
and further transformations of the obtained trifluoromethylated
compounds [10]. During our work on the trifluoromethylation of
allylsilanes [11], we observed a unique transformation: treat-
ment of (Z)-trifluoromethylated 2-phenyl allylic alcohol 1 with
n-butyllithium (n-BuLi) provided the SN20-type reaction product
2 in excellent yield (Eq. (1)) [11a]. The substrate has a tri-
substituted alkene moiety and no additive was required for this
reaction. In addition, the hydroxyl group acts as a leaving group,
suggesting the generation of Li2O during the reaction [12]. Here-
in, we report a mechanistic study on this unique SN20-type
reaction of trifluoromethylated 2-aryl allylic alcohols with
alkyllithium reagent, together with a theoretical investigation
of the mechanism.
4
(b)
OH
n-BuLi (5 equiv.)
CF3
Ph
n-hexane, 23 °C, 3 h
n-Bu
CF3
6
2: 3%
Scheme 1. Effect of the trifluoromethyl group.
86% yield (Scheme 1a). This indicates that the trifluoromethyl
group profoundly accelerates the SN20-type reaction. The trifluor-
omethyl group was considered to work not only as an electron-
withdrawing group, which electronically enhances the reactivity of
the substrate, but also as a chelating group [14]. The reaction with
(E)-isomer 6 afforded a complex mixture, and the desired product 2
was obtained in only 3% yield under the same conditions as used in
the reaction of (Z)-isomer 1 (Scheme 1b). Thus, we concluded that
the trifluoromethyl group plays a crucial role in the reaction by
chelating to lithium alkoxide and fixing the conformation of the
substrate, and its orientation in (Z)-isomer 1 is geometrically more
favorable for chelation, compared with that in (E)-isomer 6.
We then examined the influence of the aryl group on the
substrate. It is well known that styrene derivatives are good
substrates for regioselective carbolithiation using the combination
of n-BuLi and TMEDA, due to the stability of the benzyl anion
[4]. Therefore, the regioisomer 7 was used for the reaction (Scheme
2). Here, the hydroxyl group, which was regarded as the leaving
group in our SN20-type reaction was not eliminated, and substrate 7
was converted to butyl-substituted fluoroalkene 8 in 14% yield. The
corresponding SN20-type reaction product was not detected. In this
n-BuLi (5 equiv.)
OH
CF3
CF3
n-Bu
2: 94%
Ph
(1)
Et2O, -10 °C, 1 h
Ph
1
2. Results and discussion
In general, organolithium reagents exhibit various aggregation
modes depending upon the conditions; for example, solvents and
additives are well known to affect the reactivity of organolithium
reagents [13]. Hence, we first examined the solvent effect in this
SN20 reaction using 1 as a substrate in n-hexane, which has no
ability to coordinate to lithium ion (Eq. (2)). Compound 2 was
isolated in 96% yield at ambient temperature, even though the
nucleophilicity is expected to be low. This result is inconsistent
with previously reported carbolithiations of styrene derivatives
and allylic alcohols [4,5]. We anticipated that the reason for this
difference might be that the lithium alkoxide moiety generated in
situ from substrate 1 works as a directing group. We hypothesized
that fluorine of the trifluoromethyl group would coordinate to the
lithium ion of lithium alkoxide to fix the conformation of the
intermediate [14], providing an energetically favorable carbo-
lithiation pathway via structural activation of the double bond.
particular reaction system, n-BuLi appeared to attack the
position of the trifluoromethyl group instead of the -position, to
b-
a
provide intermediate A. The regioselectivity of this step was
explained by a stability of benzylic anion, and a steric effect might
participate to some extent in determination the selectivity. The
lithium alkoxide form of product 8 could then be generated via
addition-elimination of gem-difluoroalkene A. It is noteworthy
that the geometry between the phenyl group and the fluorine atom
of product 8 is trans. This strongly suggested that the alkoxide and
the fluorine atom would both coordinate to the lithium ion.
n-BuLi (5 equiv.)
OH
CF3
CF3
n-Bu
2: 96%
Ph
n-hexane, 23 °C, 3 h
(2)
Ph
n-Bu
F
1
n-BuLi (5 equiv.)
CF3
+
7: 68%
To test this idea, we chose (Z)-
a
-methyl-b-trifluoromethyl-
Ph
OH
Ph
OH n-hexane, 23 °C, 3 h
styrene 3 as a substrate (Eq. (3)). No carbolithiated product was
detected and the starting material 3 was recovered in 88% yield,
suggesting that the hydroxyl group serves not only as a leaving
group, but also as a directing group.
n-Bu
7
n-Bu
F3C
Ph
not detected
8: 14%
n-BuLi
n-BuLi (5 equiv.)
Recovery of 3
CF3
(3)
88%
Ph
n-hexane, 23 °C, 3 h
Li
O
F
Li
O
Bu
F
Ph
3
F
F
n-BuLi
Next, substrates 4 and 6 were treated with n-BuLi under the
Ph
standard conditions in order to examine the influence of the
trifluoromethyl group (Scheme 1). The reaction of 4 bearing a
methyl group instead of a trifluoromethyl group afforded only 3%
yield of alkylated product 5, and allylic alcohol 4 was recovered in
n-Bu
A
n-Bu
B
Scheme 2. Effect of the aryl group.
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3
OH
OH
F
n-BuLi (5 equiv.)
9
+
CF3
Ph
Ph
n-Bu
10
H
12%
58%
n-hexane, 23 °C, 3 h, 12%
9
Et2O, -10 °C, 1 h, 16%
O
O
Li
F
Li
F
n-BuLi
Ph
Ph
F
F
n-Bu
C
D
Scheme 3. Reaction of alkyl substrate 9.
Substrate 9 bearing a phenethyl group in place of the phenyl
group was also used as a substrate to gain further information
regarding the influence of the aryl group in this reaction (Scheme
3). However, deprotonation at the allylic position was faster than
nucleophilic attack on the vinylic carbon. The resulting intermedi-
ate C reacted with n-BuLi to afford compound 10, albeit in low
Fig. 1. Starting intermediates IM1 generated from 1 with (MeLi)4.
Fig. 2. Intramolecular pathway in the case of IM1a.
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yield. The chelation effect was considered to be important for
controlling the stereochemistry in this reaction. The reaction in n-
hexane led to a complex mixture, and 9 was recovered in only 12%
yield after column chromatography. Fortunately, the crude
mixture became relatively clean when Et2O was used as a solvent,
and 10 was obtained in 16% yield together with 58% of starting
material 9.
We then focused on the reactivity of other organometallic
reagents, as chelation by the metal ion appeared to be essential for
this reaction. Several alkyl metal reagents were screened under the
standard conditions (Table 1). Considering the commercial
availability of alkyl metal species, we selected methyl metal
compounds for this screening. Since methyllithium reagent (MeLi)
did not dissolve in n-hexane, diethyl ether (Et2O) was used as a
solvent in the screening experiments. Compound 11 bearing a
naphthyl group was chosen as a substrate, due to the somewhat
volatile nature of the product formed from the substrate bearing a
phenyl group. The reaction of 11 with MeLi in Et2O efficiently
afforded the corresponding SN20 product in 83% yield (entry 1).
However, treatment of 11 with other methyl metal species was not
effective (entries 2–4). In the case of MeMgBr, a complex mixture
was obtained (entry 2), and Me3Al and Me2Zn lead to recovery of
large amounts of starting material (entries 3 and 4). These results
indicate that the nucleophilicity of the organometallic reagent, and
Fig. 3. Carbolithiation step of (a) IM1a and (b) IM1n with (MeLi)4.
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Table 1
bridged by Li–F interaction can adopt two types of conformer
(IM1a, and IM1e). The free energies (kcal/mol) of the conformers
and IM1n without Li–F interaction were compared (Fig. 1). As
anticipated from the experimental results, intermediate IM1a was
found to be the most stable conformer, and its C–O bond lies in a
nearly perpendicular position with respect to the C55C double
bond. The conformer with Li–F interaction (IM1e), in which the
hydroxyl group is directed inwards toward the double bond to
generate allylic strain, was less stable than IM1n. The slight
energetic difference (0.2 kcal/mol) between IM1a and IM1n
indicates that Li–F interaction does not significantly affect the
thermal stability of these conformers. Bridging did not influence
Reaction with organometallic reagentsa.
OH
Me-[M]
CF3
CF3
.
Et2O, 23 °C, 9 h
Me
11
12
Entry
Nucleophile
Yield of 12 [%]b
Recovery of 11 [%]b
1
2
3
4
MeLi
83
0
43
MeMgBr
Me3Al
Me2Zn
Trace
NDc
NDc
93
˚
100
the length of the double bond (1.34 A).
a
We then examined the intramolecular reaction pathway in the
case of IM1a (Fig. 2) [17]. Based on our experimental results and
literature data [3–6], we assumed that the reaction proceeds via
The reactions were carried out with methyl metal species (5 equiv.) in Et2O on a
0.2 mmol scale.
b
Determined by 1H NMR analysis.
Not detected.
c
carbolithiation (IM1a to IM2intra) [18], followed by oxygen
elimination (IM2intra to PD). The calculation results showed that
the highest activation energy was located between IM1a and
TS1intra, which is the carbolithiation step. The activation energy of
this step was +31.7 kcal/mol, which seems to be too large for the
reaction proceeding at room temperature. Next, we focused on the
intermolecular reaction of IM1a with an extra MeLi tetramer
(MeLi)4 (Figs. 3 and 4). Carbolithiation of the double bond with
(MeLi)4 may occur from either the same (TS1) or the opposite
(TS10) side with respect to the lithium alkoxide substituent of IM1a.
TS1 was obtained via formation of intermediate IM1a2, in which
the unique chelation and aggregation modes of the lithium ion, are
important.
In order to further examine the reaction mechanism, we
conducted DFT calculations at the M06-2X/6-31+G(d,p) level of
theory [15]. In this study, the starting material was modeled as IM1
generated from allylic alcohol 1 and MeLi tetramer [16]. We first
examined an influence of the Li–F interaction to the stability of the
intermediate. The intermediate containing seven-membered ring
Fig. 4. Intermolecular pathway.
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the lithium aggregates of IM1a and (MeLi)4 were combined, whilst
TS10 was directly generated from IM1a. Comparison of the energy
levels of the transition states showed that the pathway through
TS1 (+14.7 kcal/mol from IM1a, +19.0 kcal/mol from IM1a2) is
much more favorable than the pathway through TS10 (+32.1 kcal/
mol) (Fig. 3a). In TS1, protruding MeLi of IM1a2 reacts with the
double bond. Moreover, carbolithiation of IM1n was also examined
(Fig. 3b). The transition state of the carbolithiation of IM1n with
(MeLi)4 (TS1n) was obtained without formation of an intermediate
and showed a higher energy barrier compared to TS1. We conclude
that the lithium aggregate of IM1a facilitates the desired reaction
by serving as a directing group, which leads to the larger aggregate
and generates reactive MeLi in close proximity to the double bond.
The calculated activation energy of TS1 from IM1a2 appears to be
reasonable for the reaction to occur at room temperature.
was carried out using a JIA recycling preparative HPLC system [LC-
918R; column, JAIGEL-H; chloroform]. TLC analysis was performed
on Silica gel 60 F254-coated glass plates (Merck). Visualization was
accomplished by means of ultraviolet (UV) irradiation at 254 nm or
by spraying 12-molybdo(VI)phosphoric acid ethanol solution as
the developing agent.
Dehydrated n-hexane, tetrahydrofuran (THF) and diethyl ether
(Et2O) werepurchased from Kanto Chemical Co., Inc. Other reagents
were purified by usual methods. Compounds 1 [11], 4 [19] and 7
[20] wereprepared according to literature procedures. Compound3
was obtained as a by-product in the oxy-trifuoromethylation of
methylstyrene with copper-Togni reagent system [10i].
a-
4.2. Preparation of (E)-4,4,4-trifluoro-2-phenyl-2-buten-1-ol (6)
We then calculated the entire reaction pathway for the
intermolecular reaction of IM1a with (MeLi)4 (Fig. 4). In line with
the intramolecular pathway in Fig. 2, the carbolithiation step
requires the highest activation energy in the intermolecular
reaction. Carbolithiated intermediate IM2 and the transition state
of the oxygen elimination step TS2 were also energetically
stabilized due to aggregate formation (ꢀ18.6, and ꢀ10.6 kcal/
mol, respectively). The activation energy of the oxygen elimination
Preparation of compound 6 was previously reported [11]. Col-
orless oil; 1H NMR (400 MHz, CDCl3):
= 1.86 (t, J = 6.2 Hz, 1H),
4.34–4.38 (m, 2H), 6.04 (qt, J = 8.3, 1.8 Hz, 1H), 7.19–7.22 (m, 2H),
7.36–7.40 (m, 3H); 13C NMR (100 MHz, CDCl3):
= 66.6, 114.2 (q,
J = 33.7 Hz), 123.6 (q, J = 270.7 Hz), 127.8, 128.6, 128.9, 135.6,
152.78 (q, J = 5.8 Hz); 19F NMR (376 MHz, CDCl3):
= ꢀ56.0 (d,
d
d
d
J = 8.3 Hz); IR (neat): 3343, 3060, 2915, 1682, 1276, 1214 cmꢀ1
;
HRMS (ESI+): Calcd. for [C10H9F3O+H]+: m/z = 203.0678, Found:
step was +8.0 kcal/mol. In TS2, electrons of the
p
-orbital on the
203.0677.
trigonal benzylic carbon move into the *-orbital of C–O bond
s
(nPh–C–C–O: 87.2 deg.); this could induce C–O bond cleavage,
where the Li2Oꢁ6MeLi cluster acts as a good leaving group due to
stabilization of the formal oxygen dianion by lithium aggregates.
4.3. Synthesis of (Z)-4,4,4-trifluoro-2-phenethyl-2-buten-1-ol (9)
To a solution of 4,4,4-trifluoro-2-phenethyl-1-butene [11]
(364 mg, 1.7 mmol) in CH2Cl2/phosphate buffer (pH = 7.0)
(11 mL/11 mL) was added m-CPBA (2.2 g, 9.7 mmol) at 0 8C. After
stirring for 4 h, the reaction was quenched with Na2S2O3 and the
mixture was extracted with CH2Cl2. The combined organic layer
was dried over MgSO4, and filtered. The filtrate was evaporated
under reduced pressure. Flash column chromatography (SiO2; n-
hexane/ethyl acetate = 20/1) of the residue afforded 2-phenethyl-
2-(2,2,2-trifluoroethyl)oxirane as a colorless oil (183 mg, 47%). 1H
3. Conclusion
We present the mechanistic insight into a SN20-type reaction of
(Z)-trifluoromethylated allylic alcohol with alkyl lithium reagent
in n-hexane in the absence of any additive. The stereochemistry of
the substrate is important for the reaction, in order to accelerate
the reaction and to control product formation through chelation of
the alkoxide and a fluorine atom of the trifluoromethyl group to the
lithium ion. The aryl group plays a role in controlling the
regioselectivity and also accelerates the reaction. Computational
studies were consistent with these pathways, and the lowest
energy profile was obtained when two MeLi-tetramers were
involved in the transition state. Overall, our results indicate that
the hydroxyl group becomes a good leaving group for the SN20-type
reaction through coordination to the lithium cluster. We believe
that the basic understanding of the mechanism obtained in this
work will be helpful to develop new molecular transformations
with trifluoromethylated compounds in future.
NMR (400 MHz, CDCl3):
7.17–7.22 (m, 3H), 7.27–7.31 (m, 2H); 13C NMR (100 MHz, CDCl3):
= 30.6, 36.0, 39.8 (q, J = 28.9 Hz), 52.0, 54.3 (q, J = 2.9 Hz), 125.8
(q, J = 277.4 Hz), 126.3, 128.4, 128.7, 140.9; 19F NMR (376 MHz,
d = 1.91–2.25 (m, 3H), 2.59–2.75 (m, 5H),
d
CDCl3):
d
= ꢀ62.5 (t, J = 10.4 Hz); IR (neat): 3060, 3029, 2940, 1497,
1370, 1263 cmꢀ1; HRMS (ESI+): Calcd. for [C12H13F3O+Na]+: m/
z = 253.0811, Found: 253.0813.
To a solution of 2-phenethyl-2-(2,2,2-trifluoroethyl)oxirane
(183 mg, 0.8 mmol) in THF (8 mL) was added a THF solution of
NHMDS (1.9 mL, 1 M, 1.9 mmol) at ꢀ78 8C. After stirring for 2 h at
the same temperature, the reaction was quenched with aqueous
NH4Cl. The mixture was extracted with ethyl acetate, dried over
MgSO4, and filtered. The filtrate was evaporated under reduced
pressure. Flash column chromatography (SiO2; n-hexane/ethyl
actate = 5/1) of the residue afforded the title compound 9 as a
4. Experimental
4.1. General
colorless oil (61.4 mg, 33%). 1H NMR (400 MHz, CDCl3):
d = 1.45 (t,
All reactions and manipulations were performed under an
atmosphere of dry nitrogen.
J = 6.3 Hz, 1H), 2.60 (t, J = 7.9 Hz, 2H), 2.82 (t, J = 7.9 Hz, 2H), 4.36 (d,
J = 6.3 Hz, 2H), 5.52 (q, J = 8.7 Hz, 1H), 7.18–7.24 (m, 3H), 7.29–7.32
1H, 19F NMR spectra were measured on a JEOL JNM-ECS-400
spectrometer at 400 and 376 MHz, respectively. 13C NMR spectra
were recorded on a JEOL JNM-ECS-400 spectrometer at 100 MHz.
Chemical shifts are reported downfield from TMS (=0) or CDCl3 for
1H NMR. For 13C NMR, chemical shifts are reported in the scale
relative to CDCl3. For 19F NMR, chemical shifts are reported in the
scale relative to a CFCl3 external standard (0 ppm). Infrared spectra
were measured on a Thermo Nicolet iS5, and only diagnostic
absorptions are listed below. ESI-MS was taken on Bruker
micrOTOF-QII-RSL. EI-MS was taken on a JEOL JMS-700V. Column
(m, 2H); 13C NMR (100 MHz, CDCl3):
d
= 34.1, 36.0, 60.4, 116.0 (q,
J = 33.7 Hz), 123.2 (q, J = 271.6 Hz), 126.4, 128.5, 128.7, 140.8, 153.1
(q, J = 5.8 Hz); 19F NMR (376 MHz, CDCl3):
d
= ꢀ56.1 (t, J = 8.7 Hz);
IR (neat): 3384, 3029, 2929, 1673, 1451, 1272 cmꢀ1; HRMS (ESI+):
Calcd. for [C12H13F3O+Na]+: m/z = 253.0811, Found: 253.0813.
4.4. Synthesis of (Z)-4,4,4-trifluoro-2-(2-naphthyl)-2-buten-1-ol
(11)
To a solution of 4,4,4-trifluoro-2-(2-naphthyl)-1-butene [11]
(2.3 g, 9.6 mmol) in CH2Cl2/phosphate buffer (pH = 7.0) (64 mL/
64 mL) was added m-CPBA (11 g, 4.8 mmol) at 0 8C. After stirring
chromatography was performed with silica gel N-60 (40–100
mm)
purchased from Kanto Chemical Co., Inc. In some cases, purification
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for 4 h, the reaction was quenched with Na2S2O3 and the mixture
was extracted with CH2Cl2. The combined organic layer was dried
over MgSO4, and filtered. The filtrate was evaporated under
reduced pressure. Flash column chromatography (SiO2; n-hexane/
ethyl acetate = 20/1) of the residue afforded 2-(2-naphthyl)-2-
(2,2,2-trifluoroethyl)oxirane as a colorless oil (1.1 g, 46%). 1H NMR
2930, 1684, 1467 cmꢀ1; HRMS (ESI+): Calcd. for [C18H27FO+Na]+:
m/z = 301.1938, Found: 301.1934.
4.5.3. (2Z,3Z)-4-Fluoro-2-(2-phenylethylidene)-3-octen-1-ol (10)
Colorless oil; 1H NMR (400 MHz, CDCl3):
d = 0.94 (t, J = 7.4 Hz,
3H), 1.39 (sext, J = 7.4 Hz, 2H), 1.51–1.62 (m, 2H), 1.75–1.79 (m,
1H), 2.29 (dt, J = 17.9, 7.4 Hz, 2H), 3.44 (d, J = 7.4 Hz, 2H), 4.29 (d,
J = 6.0 Hz, 2H), 5.38 (d, J = 43.2 Hz, 1H), 5.69 (t, J = 7.4 Hz, 1H), 7.18–
7.22 (m, 3H), 7.27–7.31 (m, 2H); 13C NMR (100 MHz, CDCl3):
(400 MHz, CDCl3):
7.48–7.51 (m, 3H), 7.83–7.88 (m, 4H); 13C NMR (100 MHz, CDCl3):
= 41.0 (q, J = 28.9 Hz), 54.5, 55.8 (q, J = 2.9 Hz), 123.7, 125.5, 125.6
(q, J = 277.4 Hz), 126.6, 126.6, 127.8, 128.2, 128.5, 133.1, 135.5; 19
d = 2.77–3.02 (m, 3H), 3.18 (d, J = 5.1 Hz, 1H),
d
F
d = 13.9, 22.2, 28.6, 32.8 (d, J = 27.9 Hz), 34.6, 66.9 (d, J = 5.78 Hz),
NMR (376 MHz, CDCl3):
d
= ꢀ61.6 (t, J = 10.4 Hz); IR (neat): 3059,
100.6 (d, J = 11.6 Hz), 126.3, 128.6, 128.6, 129.1, 133.6 (d,
J = 2.9 Hz), 140.4, 161.2 (d, J = 264.9 Hz); 19F NMR (376 MHz,
1768, 1575, 1425, 1366, 1131 cmꢀ1; HRMS (ESI+): Calcd. for
[C14H11F3O+H]+: m/z = 253.0835, Found: 253.0835.
CDCl3):
d
= ꢀ99.2 (dt, J = 43.2, 17.9 Hz); IR (neat): 3421, 2958,
To a solution of 2-(2-naphthyl)-2-(2,2,2-trifluoroethyl)oxirane
(1.1 g, 4.4 mmol) in THF (44 mL) was added to a THF solution of
NHMDS (5.3 mL, 1 M, 5.3 mmol) at ꢀ78 8C. After stirring for 2 h at
the same temperature, the reaction was quenched with aqueous
NH4Cl. The mixture was extracted with ethyl acetate, dried over
MgSO4, and filtered. The filtrate was evaporated under reduced
pressure. Flash column chromatography (SiO2; n-hexane/diethyl
ether = 5/1) of the residue afforded the title compound 11 as a
colorless oil (818 mg, 74%). 1H NMR (400 MHz, CDCl3):
J = 6.8 Hz, 1H), 4.84 (d, J = 6.8 Hz, 2H), 6.08 (q, J = 8.7 Hz, 1H), 7.51–
7.55 (m, 2H), 7.59 (dd, J = 8.5, 1.8 Hz, 1H), 7.84–7.90 (m, 3H), 8.01
(d, J = 1.4 Hz, 1H); 13C NMR (100 MHz, CDCl3):
2930, 1683, 1454 cmꢀ1; HRMS (ESI+): Calcd. for [C16H21FO+Na]+:
m/z = 271.1469, Found: 271.1471.
4.5.4. 4,4,4-Trifluoro-3-methyl-2-(2-naphthyl)-1-butene (12)
Colorless oil; 1H NMR (400 MHz, CDCl3):
d
= 1.44 (d, J = 7.4 Hz,
3H), 3.49–3.61 (m, 1H), 5.51 (s, 1H), 5.63 (s, 1H), 7.45–7.51 (m, 3H),
7.78–7.85 (m, 4H); 13C NMR (100 MHz, CDCl3):
= 15.0 (q,
d
J = 2.89 Hz), 42.7 (q, J = 27.0 Hz), 117.4, 124.9, 125.4, 126.3,
126.5, 127.4 (q, J = 280.3 Hz), 127.7, 128.2, 128.3, 132.9, 133.4,
d = 1.64 (t,
139.2, 145.0; 19F NMR (376 MHz, CDCl3):
d
= ꢀ70.4 (d, J = 8.7 Hz);
IR (neat): 3059, 2991, 1626, 1641, 1382, 1167, 1137, 1091 cmꢀ1
;
d
= 59.8, 118.0 (q,
HRMS (ESI+): Calcd. for [C15H13F3O+H]+: m/z = 251.1042, Found:
J = 34.7 Hz), 123.3 (q, J = 270.7 Hz), 124.2, 126.8, 126.9, 127.1,
127.8, 128.6, 128.8 133.3, 133.7, 134.8, 151.4 (q, J = 5.8 Hz); 19F
251.1042.
NMR (376 MHz, CDCl3):
d
= ꢀ55.6 (t, J = 8.7 Hz); IR (neat): 3370,
4.6. DFT study
3061, 1647, 1436, 1326, 1195 cmꢀ1; HRMS (ESI+): Calcd. for
[C14H11F3O+H]+: m/z = 253.0835, Found: 253.0835.
All calculations were carried out with the Gaussian 09 program
package. Structural optimization and vibrational analyses were
performed using M06-2X with the 6-31+G(d,p) basis set. Gibbs
energies (kcal/mol) obtained by vibrational analyses are presented
in the text. No imaginary frequency for intermediates and one
imaginary frequency for each transition state were observed.
Reaction pathways from the transition states were confirmed by
IRC calculation and the vibration modes of their imaginary
frequencies.
4.5. Typical experimental procedure for SN20-type reaction of 1 in n-
hexane
To a solution of 1 (21.0 mg, 0.1 mmol) in n-hexane (1 mL) was
added an n-hexane solution of n-butyl lithium reagent (1.6 M,
0.33 mL, 0.5 mmol) at 0 8C. The reaction mixture was stirred for 3 h
at 23 8C, and then the reaction was quenched with 1 N HCl on an ice
bath. The mixture was extracted with ethyl acetate, and the
combined organic layer was dried over MgSO4, and filtered. The
filtrate was evaporated under reduced pressure. Flash column
chromatography (SiO2; n-hexane) of the residue afforded com-
pound 2 as a colorless oil (24.1 mg, 96%). 1H NMR (400 MHz,
Acknowledgements
This work was supported by RIKEN and Japan Science and
Technology Agency. All calculations were conducted on the RIKEN
Integrated Cluster of Clusters (RICC). We are grateful to Dr. Ryo
Takita (Tokyo University, RIKEN CSRS) and Prof. Teiji Chihara
(Saitama University) for helpful discussions.
CDCl3):
1H), 1.87–1.95 (m, 1H), 3.16–3.27 (m, 1H), 5.40 (s, 1H), 5.55 (s, 1H),
7.27–7.37 (m, 5H); 13C NMR (100 MHz, CDCl3):
= 13.8, 22.5, 28.9,
29.2, 48.2 (q, J = 26.0 Hz), 117.1 126.4, 127.0 (q, J = 279.4 Hz),
127.6, 128.4, 142.5, 143.8; 19F NMR (376 MHz, CDCl3):
= ꢀ69.2 (d,
J = 8.7 Hz); IR (neat): 3060, 3026, 2958, 2933, 2874, 1631, 1600,
d = 0.85–0.89 (m, 3H), 1.23–1.46 (m, 4H), 1.69–1.79 (m,
d
d
Appendix A. Supplementary data
1262, 1163, 1131, 777, 699 cmꢀ1
;
HRMS (EI+): Calcd. for
[C14H17F3+H]+: m/z = 242.1282, Found: 242.1286.
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.jfluchem.2015.
07.024.
4.5.1. 2-Phenyl-3-methyl-1-heptene (5)
Compound 5 was obtained using the same procedure as
described for 2 in 3% yield. The spectra were consistent with
reported data [21].
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