Unusual reaction course of styrenes to 2-arylethyltriphenylphosphonium salts

Article abstract of DOI:10.1246/bcsj.80.1785

1-Arylethyltriphenylphosphonium bromides thermally rearranged to 2-arylethyltriphenylphosphonium bromides. Direct formation of 2-arylethylphosphonium bromides was achieved by reacting styrene, HBr, and triphenylphosphine. On the other hand, thermolysis of

Full text of DOI:10.1246/bcsj.80.1785

Ó 2007 The Chemical Society of Japan
Bull. Chem. Soc. Jpn. Vol. 80, No. 9, 1785–1790 (2007) 1785
Unusual Reaction Course of Styrenes
to 2-Arylethyltriphenylphosphonium Salts
ꢀ
Kentaro Okuma, Koichiro Yoshitake, Toshiharu Izaki, Keiko Yoshida, and Kosei Shioji
Department of Chemistry, Faculty of Science, Fukuoka University, Jonan-ku, Fukuoka 814-0180
Received February 13, 2007; E-mail: kokuma@fukuoka-u.ac.jp
1-Arylethyltriphenylphosphonium bromides thermally rearranged to 2-arylethyltriphenylphosphonium bromides.
Direct formation of 2-arylethylphosphonium bromides was achieved by reacting styrene, HBr, and triphenylphosphine.
On the other hand, thermolysis of 1-indanyltriphenylphosphonium bromide gave indene and triphenylphosphonium bro-
mide. From deuterium and 13C-labeled experiments, the interconversion of primary and secondary cation intermediates
was suggested. No neighboring phenyl group (phenonium cation intermediate) interaction was observed.
From the original work of Wittig and Geissler, Wittig re-
agents have played an important role in the synthesis of ole-
fins.1 Substituted 2-arylethyltriphenylphosphonium salts 1 are
21.9 kJ/mol
very important precursors for the synthesis of benzo[j]fluo-
ranthene,2 (Z)-penta-1,3-dienes,3 quinuclidines, which are anti-
arrhythmic agents,4 and aryl-substituted alkenes.5 Methods
for the preparation of phenethyltriphenylphosphonium salts 1
include the reaction of phenethyl halides with triphenylphos-
phine,6 the reaction of 2-phenylethanol with triphenylphos-
phine and acids,7 and the reaction of methylenetriphenylphos-
phorane with substituted benzyl halides.3 However, these
methods are limited due to the availability of substituted 2-
arylethyl halides and 2-arylethanols. We have reported a novel
synthesis of substituted 1-arylethyltriphenylphosphonium salts
2 by the reaction of styrenes 3 with triphenylphosphine in the
presence of acid.8 Recent reports on the palladium-catalyzed
synthesis of alkylphosphonium salts9 and deuterium-labeled
synthesis of primary phosphonium salts10 prompted us to
investigate the thermal transformation of 2 to 1. We report
herein a new synthesis of 1 from 1-arylethylphosphonium salts
2 and one-pot synthesis of salts 1 from substituted styrenes 3.
1a
2a
H2
C
H3C
PPh3
CH PPh3
C
H2
Br
Br
Fig. 1.
H3C
HC
CH2
PPh3
CH PPh3
Br
+
Br
2b
1b
3b
H3C
CH Br
+
+
Ph3PH Br
Results and Discussion
5
4b
Generally, secondary carbocations are more stable than
primary carbocations, whereas, at higher temperature, steric
hindrance is more important for the stability of carbocations.
Thus, it should be possible to synthesize primary phosphonium
salts by rearrangement of secondary phosphonium salts. We
first tried DFT calculations on 1-phenylethyltriphenylphospho-
nium bromide (2a) and phenylethyltriphenylphosphonium
bromide (1a). As 1a is an isomer of 2a, the stabilities of 1a and
2a were compared. By means of geometry optimization and
frequency calculation at the B3LYP/6-31G(d,p) level,11 1a
was calculated to be 21.9 kJ molꢁ1 more stable than 2a in the
ground state (S0) (Fig. 1). Thus, at elevated temperatures, it is
possible that 1-arylethylphosphonium salts 2 will rearrange to
2-arylethylphosphonium salts 1.
Scheme 1.
of the products was calculated by integral ratio (NMR) of
the products, and they are shown in Table 1. Thermolysis of
2b under several temperature (220–300 ꢂC) led to 1b in low
yields (Entries 1–6). Only 25% of 2-p-tolylethyltriphenylphos-
phonium bromide (1b) formed (Entry 5). However, when salt
2b was heated at 230–270 ꢂC in the presence of triphenylphos-
phine (0.1 molar amount), as much as 52% of 2b was convert-
ed into 1b along with 1-p-tolylethyl bromide (4b) and p-meth-
ylstyrene (3b) (Entries 7–9). When the reaction was carried
out in the presence of 0.3 molar amount of triphenylphosphine,
the conversion of 1b was up to 75% (Entry 11). Further addi-
tion of triphenylphosphine did not change the yield of 1b
(Entry 12). Thus, on a preparative scale, the rearrangement
was carried out at 260–270 ꢂC in the presence of 0.3 molar
amount of triphenylphosphine (Scheme 2). The corresponding
First, we tried the thermal rearrangement of 1-p-tolylethyl-
triphenylphosphonium bromide (2b) under several conditions
in an NMR tube (0.05 mmol scale) (Scheme 1). The yields
Published on the web September 13, 2007; doi:10.1246/bcsj.80.1785

1786 Bull. Chem. Soc. Jpn. Vol. 80, No. 9 (2007)
Table 1. Thermal Rearrangement of 2b to 1b
From Styrene to 2-Arylethylphosphonium Salts
Conditions
Time/min
Products (Yield/%)
Entry
Temp/ꢂC
Ph3P/mol amt.
2b
1b
4b
3b
1
2
3
4
5
6
7
8
9
220
230
240
240
260
300
230
250
270
270
270
270
35
25
25
15
25
15
25
30
15
30
60
60
0
0
0
0
0
0
0.1
0.1
0.1
0.3
0.3
0.5
95
75
50
45
45
7
25
21
26
8
0
5
5
0
5
15
15
15
3
0
0
5
10
15
42
0
3
5
5
6
12
25
10
15
52
43
72
75
76
5
12
10
5
5
4
10
11
12
3
4
5
Ph
H3C
H
P
CH PPh3
Br
Ph
Ph
HC
PPh3
PPh3
BPh4
PPh3
265-280 °C
NaBPh4
Br
CH2
NaBPh4
+
R
R
R
BPh4
R
Br
Ar
2a, R = H
1a, R = H
7a: Ar = C6H5
7a, R = H
3a: Ar = C6H5
2b, R = CH3
2c, R = Cl
2d, R = Br
2e, R = CF3
1b, R = CH3
1c, R = Cl
1d, R = Br
1e, R = CF3
7b: Ar = p-MeC6H4
7c: Ar = p-ClC6H4
7d: Ar = p-BrC6H4
7b, R = CH3
7c, R = Cl
7d, R = Br
7e, R = CF3
3b
: Ar = p-MeC6H4
3c
: Ar = p-ClC6H4
3d: Ar = p-BrC6H4
3e: Ar = p-CF3C6H4
7e
: Ar = p-CF3C6H4
Scheme 3.
Scheme 2.
Table 2. Thermal Rearrangement of 2
PPh3
CH2
CH
R
Ph
Ph
Ph
NaBPh4
270 °C
Salt 2
Temp/ꢂC
Time/min
7
Yield/%
+
H P
2a
2b
2c
2d
2e
270
270
265
260
270
50
50
45
45
40
7a
7b
7c
7d
7e
60
61
62
62
61
R
BPh4
7f, R = CH3 62%
7g, R = Cl 61%
Br
3f, R = CH3
3g, R = Cl
5
Scheme 4.
2-arylethylphosphonium bromides (1a–1e) were obtained in
moderate yields. Since 1a–1e are hygroscopic glassy solids,
elemental analyses were carried out by changing them into
their tetraphenylborates (7a–7e). The result are shown in
Table 2.
2-arylethyltriphenylphosphonium bromides (1f and 1g) in
moderate yields (Scheme 4).
We next tried the reaction of other primary phosphonium
salts. Heating of sec-butyltriphenylphosphonium bromide
(2h) at 275 ꢂC for 20 min led to triphenylphosphonium bro-
mide. Heating of 1-indanyltriphenylphosphonium bromide
(2i) at 275 ꢂC for 20 min led to indene and triphenylphospho-
nium bromide. These results are similar to that of Bestmann et
al.13 They have reported the thermolysis of 2i under reduced
pressure at 300 ꢂC, which results in the formation of indene
and triphenylphosphonium bromide (Scheme 5), suggesting
that aromatic groups in 2a–2g play an important role in the
formation of phosphonium salts 1a–1g.
Thus, there are two reaction pathways for the present reac-
tion. Heating of phosphonium salt 2 gives a secondary carbo-
cation. If hydrogen abstraction occurs, styrene 3 is afforded,
other hand, if the carbocation reacts with a bromide anion,
1-aryl-1-bromoethane 4 is produced. Quite a few secondary
carbocation rearranged to give primary carbocation, which
was attacked by triphenylphosphine to give 1 (Route A). In
Since 1-arylethyltriphenylphosphonium bromides 2 were
synthesized by the reaction of styrenes 3 with triphenylphos-
phonium bromide,8 an one-pot synthesis of 2-arylethyltriphen-
ylphosphonium bromides 1 from styrenes 3 was carried out. As
shown in Scheme 3, 2-(p-chlorophenyl)ethyltriphenylphos-
phonium bromide (1c) (then 7c) was readily obtained from
p-chlorostyrene (3c) by treatment with triphenylphosphine
hydrobromide. This transformation constitutes an extremely
practical one-pot synthesis of 2-arylethyltriphenylphospho-
nium salts. Unreacted styrene and by-products, such as hydro-
gen bromide and 1-p-chlorophenyl-1-bromoethane, were easi-
ly separated by treating with a base and washing with ether. It
should be noted that this salt has previously been synthesized
from p-chlorostyrene by a multi-step procedure.12
Other o-substituted styrenes (3f and 3g) also rearranged to

K. Okuma et al.
Bull. Chem. Soc. Jpn. Vol. 80, No. 9 (2007) 1787
H3C
H3C
275 °C
H3C
5
LiAlD4
CDPPh3
CD OH
Ph3PH Br
C
O
THF
reflux
PPh3
170 °C
no solvent
5
Br
Br
Br
2h
2i
Cl
Cl
Cl
1-D-2c
275 °C
Cl
(D)
270 °C
30 min
C
no solvent
C
PPh3
PPh3
(D)
+ 5
Br
1,2-D-1c
Scheme 5.
Methylene proton ratio
C1 : C2 = 42:58
Scheme 7.
H
C
H
Route A
H
H
DBU
CH2
H3C
C
H
C
O
C
13CH2
13CH3 PPh3
I
+
Ph3P
2
1
R
2-13C-3c
R
Cl
Cl
13CH3
Cl
H
H
Ph3PH Br
Route B
Ph3P
+
C
3 and 4
C
H
13CH2
CH PPh3
H
170 °C
then 260 °C
CH2
1-13C-1c
1
PPh3
Br
Cl
Br
2-13C-2c
R
Scheme 6.
Scheme 8.
the second route, interconversion of the primary and secondary
carbocation is stabilized by a neighboring aromatic group (an-
chimeric assistance).14,15 The intermediate cation (phenonium
ion) is attacked by triphenylphosphine to produce 1-arylethyl-
phosphonium bromide 1 (Route B) (Scheme 6).
In conclusion, we developed a general synthesis of 2-aryl-
ethyltriphenylphosphonium bromides from the corresponding
1-arylethylphosphonium bromides, styrenes, or 1-arylethanols.
The reaction might proceed through interconversion of secon-
dary to primary cation intermediates.
To confirm the reaction mechanism, the following deu-
terium-labeled experiment was carried out (Scheme 7). 1-(p-
Chlorophenyl)-1-deuteroethyltriphenylphosphonium bromide
(1-D-2c) was synthesized by the reaction of 5 with 1-(p-chloro-
phenyl)-1-deuteroethanol, prepared from p-chloroacetophe-
none and lithium aluminum-d4-hydride. Thermolysis of 1-D-
2c in the presence of triphenylphosphine (0.3 molar amount)
gave a mixture of 2-p-chlorophenyl-1-deuterioethyltriphenyl-
phosphonium bromide (1-D-1c) and 2-(p-chlorophenylethyl)-
1,2-d2-triphenylphosphonium bromide (1,2-D-1c) (42:58 ratio),
suggesting that the rearrangement proceeds through intercon-
version of primary and secondary carbocation.
Experimental
General. All solvents were distilled before use, and no further
treatment was carried out. NMR spectra were measured on a
Varian Innova-400 (400 MHz for 1H, 100 MHz for 13C). The
melting points were uncorrected. The reagents were purchased
from TCI and used without purification.
Material. 1-Arylethyltriphenylphosphonium bromides 2a–2d
were synthesized by the reaction of styrenes with triphenylphos-
phonium bromide.8 2-Arylethyltriphenylphosphonium bromides
(1a–1d) were already reported in the literature.5,16,17 However,
there are no spectroscopic and melting points’ data due to their
hygroscopic nature.
Since this result cannot confirm the existence of phenonium
cation, we then carried out the 13C-labeled experiment as
follows. Treatment of (p-chlorophenyl)ethene-2-13C (2-13C-
3c), prepared from methyl-13C-triphenylphosphonium iodide,
DBU, and p-chlorobenzaldehyde, with triphenylphosphonium
bromide in the presence of triphenylphosphine (0.3 molar
amount) resulted in the formation of a mixture of 1-(p-chloro-
phenyl)-2-13C-ethyltriphenylphosphonium bromide (2-13C-2c)
and 2-(p-chlorophenyl)ethyl-1-13C-triphenylphosphonium bro-
mide (1-13C-1c) (1:4 ratio) (Scheme 8). This result clearly
shows that the reaction does not proceed through phenonium
ion intermediates (Route B) but through interconversion of
secondary and primary cation intermediates (Route A).
Synthesis of 1-(p-Trifluoromethylphenyl)ethyltriphenyl-
phosphonium Bromide 2e. A mixture of p-trifluoromethylsty-
rene (0.947 g, 5.5 mmol) and triphenylphosphonium bromide pre-
pared from triphenylphosphine (1.31 g, 5.0 mmol) and hydrobro-
mic acid (48% aqueous solution, 0.57 mL, 5.0 mmol) was heated
at 170 ꢂC for 20 min and then cooled to rt. The resulting solid
was recrystallized from ethanol to give salt 2e (1.96 g, 3.8 mmol).
colorless crystals; mp 226–228 ꢂC, 1H NMR (400 MHz, CDCl3): ꢀ
1.82 (dd, 3H, J ¼ 7:6 Hz, JPH ¼ 18:8 Hz, CH3), 7.29 (dq, 1H, J ¼
6:8 Hz, JPH ¼ 13:6 Hz, CH), 7.43 (s, 4H, Ar), 7.62–7.71 (m, 6H,
Ph), 7.70–7.83 (m, 3H, Ph), 7.87–7.96 (m, 6H, Ph). 13C NMR
(100 MHz, CDCl3): ꢀ 17.11 (CH3), 34.20 (d, JPC ¼ 44 Hz, CH),
117.52 (JPC ¼ 83 Hz, PPh3), 123.86 (q, JCF ¼ 270 Hz, CF3),

1788 Bull. Chem. Soc. Jpn. Vol. 80, No. 9 (2007)
From Styrene to 2-Arylethylphosphonium Salts
125.66 (Ar), 130.40 (Ar), 130.55 (d, JPC ¼ 12 Hz, PPh3), 131.15
(Ar), 134.75 (d, JPC ¼ 9 Hz, PPh3), 135.25 (d, JPC ¼ 12 Hz,
PPh3), 138.30 (d, Jpc ¼ 13 Hz, Ar). Anal. Calcd for C27H23BrF3P:
C, 62.93; H, 4.50%. Found: C, 62.72; H, 4.64%.
PPh3), 129.06 (ClC6H4), 130.46 (ClC6H4), 130.76 (d, JPC ¼ 13
Hz, PPh3), 133.02 (ClC6H4), 134.01 (d, JPC ¼ 10 Hz, PPh3),
135.35 (d, JPC ¼ 3 Hz, PPh3), 136.92 (d, JPC ¼ 14 Hz, ClC6H4).
Salt 7c: colorless crystals. mp 203–205 ꢂC, 1H NMR (400 MHz,
CDCl3): ꢀ 2.52–2.61 (m, 2H, CH2), 2.62–2.76 (m, 2H, CH2),
6.71 (d, 2H, J ¼ 8:0 Hz, ClC6H4), 6.79–6.84 (m, 4H, BPh4),
6.90–6.96 (m, 8H, BPh4), 7.11 (d, 2H, J ¼ 8:0 Hz, ClC6H4),
7.20–7.28 (m, 6H, PPh3), 7.41 (br, 8H, BPh4), 7.50–7.80 (m,
6H, PPh3), 7.72–7.80 (m, 3H, PPh3). 13C NMR (100 MHz, CD3-
SOCD3): ꢀ 22.20 (d, JPC ¼ 48 Hz, CH2), 27.45 (CH2), 118.71
(d, JPC ¼ 86 Hz, PPh3), 122.23 (BPh4), 125.98 (BPh4), 129.05
(ClC6H4), 130.86 (ClC6H4), 130.92 (d, JPC ¼ 13 Hz, PPh3),
132.12 (ClC6H4), 134.22 (d, JPC ¼ 10 Hz, PPh3), 135.64 (PPh3),
136.17 (BPh4), 138.38 (d, JPC ¼ 17 Hz, ClC6H4), 163.97 (q,
JBC ¼ 49 Hz, BPh4). Anal. Calcd for C50H43BClP: C, 83.28; H,
6.01%. Found: C, 83.24; H, 6.30%.
Salt 1d: hygroscopic glassy solid: 1H NMR (400 MHz, CDCl3):
ꢀ 2.95–3.09 (m, 2H, CH2), 4.22–4.34 (m, 2H, CH2), 7.23–7.30 (m,
4H, BrC6H4), 7.60–7.95 (m, 15H, PPh3). 13C NMR (100 MHz,
CDCl3): ꢀ 24.11 (d, JPC ¼ 48 Hz, CH2), 27.70 (CH2), 117.66 (d,
JPC ¼ 86 Hz, PPh3), 120.60 (BrC6H4), 130.59 (d, JPC ¼ 12 Hz,
PPh3), 130.70 (BrC6H4), 131.59 (BrC6H4), 133.65 (d, JPC ¼ 11
Hz, PPh3), 135.20 (d, JPC ¼ 2 Hz, PPh3), 137.28 (d, JPC ¼ 15
Hz, BrC6H4). Salt 7d: colorless crystals, mp 211–212 ꢂC, 1H NMR
(400 MHz, CD3SOCD3): ꢀ 2.70–2.86 (m, 2H, CH2), 3.80–3.90
(m, 2H, CH2), 6.70–6.78 (m, 4H, BPh4), 6.80–6.90 (m, 8H, BPh4),
7.14 (br, 8H, BPh4), 7.21 (d, 2H, J ¼ 8:0 Hz, BrC6H4), 7.45 (d,
2H, J ¼ 8:0 Hz, BrC6H4), 7.65–7.90 (m, 15H, PPh3). 13C NMR
(100 MHz, CD3SOCD3): ꢀ 22.12 (d, JPC ¼ 49 Hz, CH2), 27.55
(CH2), 118.77 (d, JPC ¼ 86 Hz, PPh3), 120.60 (BrC6H4), 122.26
(BPh4), 126.02 (BPh4), 130.97 (d, JPC ¼ 12 Hz, PPh3), 131.31
(BrC6H4), 132.02 (BrC6H4), 134.29 (d, JPC ¼ 10 Hz, PPh3),
135.66 (PPh3), 136.20 (BPh4), 138.90 (d, JPC ¼ 17 Hz, BrC6H4),
164.00 (q, JBC ¼ 49 Hz, BPh4). Anal. Calcd for C50H43BBrP: C,
78.44; H, 5.66%. Found: C, 78.40; H, 5.87%.
Salt 1e: hygroscopic glassy solid. 1H NMR (400 MHz, CDCl3):
ꢀ 3.09–3.22 (m, 2H, CH2), 4.31–4.42 (m, 2H, CH2), 7.48–7.59 (m,
4H, CF3C6H4), 7.60–7.95 (m, 15H, PPh3). 13C NMR (100 MHz,
CDCl3): ꢀ 24.30 (d, JPC ¼ 50 Hz, CH2), 28.20 (d, JPC ¼ 3 Hz,
CH2), 117.79 (d, JPC ¼ 86 Hz, PPh3), 124.18 (q, JCF ¼ 270 Hz,
CF3), 125.63 (d, JPC ¼ 4 Hz, CF3C6H4), 129.02 (d, JCF ¼ 32 Hz,
CF3C6H4), 129.42 (CF3C6H4), 130.72 (d, JPC ¼ 13 Hz, PPh3),
133.80 (d, JPC ¼ 11 Hz, PPh3), 135.36 (d, JPC ¼ 3 Hz, PPh3),
142.41 (d, JPC ¼ 14 Hz, CF3C6H4). Salt 7e: colorless solid; mp
188–190 ꢂC. 1H NMR (400 MHz, CDCl3): ꢀ 2.48–2.58 (m, 2H,
CH2), 2.65–2.80 (m, 2H, CH2), 6.75–6.97 (m, 14H, BPh4),
7.20–7.28 (m, 6H, PPh3 and CF3C6H4), 7.34–7.43 (m, 10H, BPh4
and CF3C6H4), 7.48–7.58 (m, 6H, PPh3), 7.70–7.79 (m, 3H,
PPh3). 13C NMR (100 MHz, CD3SOCD3): ꢀ 22.01 (d, JPC ¼ 49
Hz, CH2), 27.90 (CH2), 118.64 (d, JPC ¼ 85 Hz, PPh3), 122.27
(BPh4), 124.92 (q, JCF ¼ 270 Hz, CF3), 125.99 (CF3C6H4),
126.02 (BPh4), 128.23 (q, JCF ¼ 32 Hz, CF3C6H4), 129.90 (CF3-
C6H4), 130.97 (d, JPC ¼ 12 Hz, PPh3), 134.23 (d, JPC ¼ 10 Hz,
PPh3), 135.68 (PPh3), 136.20 (BPh4), 144.24 (d, JPC ¼ 17 Hz,
CF3C6H4), 164.00 (q, JBC ¼ 49 Hz, BPh4). Anal. Calcd for
C51H43BF3P: C, 81.17; H, 5.74%. Found: C, 80.92; H, 6.01%.
Synthesis of 1c from p-Chlorostyrene. A mixture of triphen-
ylphosphine (0.68 g, 2.6 mmol) and hydrobromic acid (48% in
water, 0.34 mL, 2.0 mmol) was heated to 130 ꢂC for 5 min. p-
Chlorostyrene (3c) (0.31 g, 2.2 mmol) was added to the mixture
and heated to 270 ꢂC for 50 min. The reaction mixture was cooled
to rt. The obtained pale brown glassy solid was dissolved in di-
Thermal Rearrangement of 1-Phenethyltriphenylphospho-
nium Bromide (2a) to Phenylethyltriphenylphosphonium Bro-
mide (1a). A mixture of phosphonium bromide 2a (0.67 g, 1.5
mmol) and triphenylphosphine (0.12 g, 0.45 mmol) was heated
to 270 ꢂC for 50 min and cooled to rt. The obtained pale brown
glassy solid was dissolved in dichloromethane (30 mL), washed
with aq. sodium carbonate (5%, 10 mL ꢃ 3), dried over magne-
sium sulfate, and filtered, and the solvent was evaporated to give
a mixture of 1a, triphenylphosphine, and small amount of triphen-
ylphosphine oxide. The glassy solid was crushed, washed with
ether (10 mL ꢃ 3) to give pale brown glassy solid of 1a. The solid
was dissolved in acetone and was added to a solution of sodium
tetraphenylborate (0.41 g, 1.2 mmol) in acetone (10 mL). The sus-
pension was filtered and evaporated to give colorless solid, which
was recrystallized from dichloromethane–ether to afford colorless
crystals of 7a (0.61 g, 0.92 mmol). Salt 1a: hygroscopic glassy
solid, 1H NMR (400 MHz, CDCl3): ꢀ 3.03–3.13 (m, 2H, CH2),
4.20–4.29 (m, 2H, CH2), 7.36–7.56 (m, 4H, Ar), 7.60–7.95 (m,
15H, PPh3). 13C NMR (100 MHz, CDCl3): ꢀ 24.89 (d, JPC ¼ 47
Hz, CH2), 28.58 (CH2), 118.37 (d, JPC ¼ 86 Hz, PPh3), 127.28
(Ph), 129.08 (Ph), 130.72 (d, JPC ¼ 13 Hz, PPh3), 133.28 (Ph),
134.01 (d, JPC ¼ 10 Hz, PPh3), 135.81 (PPh3), 138.41 (d, JPC
¼
13 Hz, Ph). Salt 7a: colorless crystals. mp 196–198 ꢂC. H NMR
(400 MHz, CDCl3): ꢀ 2.68–2.80 (m, 4H, CH2CH2), 6.76–6.82
(m, 4H, BPh4), 6.88–6.93 (m, 8H, BPh4), 7.20–7.26 (m, 13H,
Ph and BPh4), 7.39 (br, 6H, PPh3), 7.46–7.54 (m, 6H, PPh3),
7.69–7.76 (m, 3H, PPh3). 13C NMR (100 MHz, CD3SOCD3): ꢀ
22.12 (d, JPC ¼ 48 Hz, CH2), 28.11 (CH2), 118.86 (d, JPC ¼ 86
Hz, PPh3), 122.22 (BPh4), 125.95 (BPh4), 127.50 (Ph), 128.93
(Ph), 129.22 (Ph), 130.92 (d, JPC ¼ 12 Hz, PPh3), 134.27 (d,
JPC ¼ 10 Hz, PPh3), 135.64 (PPh3), 136.18 (BPh4), 139.53 (d,
JPC ¼ 17 Hz, Ph), 163.99 (q, JBC ¼ 49 Hz, BPh4). Anal. Calcd
for C50H44BP: C, 87.46; H, 6.46%. Found: C, 87.08; H, 6.64%.
Other reaction was carried out in a similar manner.
1
Salt 1b: hygroscopic glassy solid, 1H NMR (400 MHz, CDCl3):
ꢀ 2.27 (s, 3H, TolMe), 2.96–3.07 (m, CH2), 4.09–4.19 (m, CH2),
7.03 (d, 2H, J ¼ 8:0 Hz, Tol), 7.15 (d, 2H, J ¼ 8:0 Hz, Tol), 7.60–
7.89 (m, 15H, PPh3). 13C NMR (100 MHz, CDCl3): ꢀ 21.22 (Me),
25.02 (d, JPC ¼ 48 Hz, CH2), 28.15 (CH2), 117.26 (d, JPC ¼ 85
Hz, PPh3), 128.78 (Tol), 129.74 (Tol), 130.75 (d, JPC ¼ 12 Hz,
PPh3), 133.92 (d, JPC ¼ 10 Hz, PPh3), 134.90 (Tol), 135.31 (d,
JPC ¼ 32 Hz, PPh3), 136.93 (Tol). Salt 7b: mp 176–178 ꢂC,
1H NMR (400 MHz, CDCl3): ꢀ 2.29 (s, 3H, CH3), 2.65–2.78 (m,
4H, CH2), 6.75–6.83 (m, 6H, Tol + BPh4), 6.90–6.96 (m, 8H,
BPh4), 7.01 (d, 2H, J ¼ 8:0 Hz, Tol), 7.20–7.28 (m, 8H, BPh4),
7.39 (br, 6H, PPh3), 7.49–7.58 (m, 6H, PPh3), 7.70–7.78 (m, 3H,
PPh3). 13C NMR (100 MHz, CD3SOCD3): ꢀ 21.22 (Me), 22.53 (d,
JPC ¼ 51 Hz, CH2), 27.70 (CH2), 118.82 (d, JPC ¼ 86 Hz, PPh3),
122.20 (BPh4), 125.96 (BPh4), 128.78 (Tol), 129.72 (Tol), 130.88
(d, JPC ¼ 12 Hz, PPh3), 134.20 (d, JPC ¼ 10 Hz, PPh3), 134.82
(Tol), 135.57 (PPh3), 136.15 (BPh4), 136.49 (d, JPC ¼ 21 Hz,
Tol), 163.97 (q, JBC ¼ 49 Hz, BPh4). Anal. Calcd for C51H46BP:
C, 87.42; H, 6.62%. Found: C, 87.27; H, 6.78%.
Salt 1c: hygroscopic glassy solid. 1H NMR (400 MHz, CDCl3):
ꢀ 2.96–3.07 (m, CH2), 4.09–4.19 (m, CH2), 7.03 (d, 2H, J ¼ 8:0
Hz, ClC6H4), 7.15 (d, 2H, J ¼ 8:0 Hz, ClC6H4), 7.60–7.89 (m,
15H, PPh3). 13C NMR (100 MHz, CDCl3): ꢀ 24.76 (d, JPC ¼ 48
Hz, CH2), 28.01 (d, JPC ¼ 2 Hz, CH2), 118.23 (d, JPC ¼ 85 Hz,

K. Okuma et al.
Bull. Chem. Soc. Jpn. Vol. 80, No. 9 (2007) 1789
chloromethane, washed with aq. sodium carbonate, extracted with
dichloromethane, dried over magnesium sulfate and filtered, and
the solvent was evaporated to give pale yellow glassy solid of
crude 1c (0.60 g, 1.24 mmol).
identical to the authentic sample. The remaining solid was mainly
triphenylphosphonium bromide (0.045 g, 0.13 mmol).
Synthesis of Deuterated Phosphonium Salt 1-D-2c. To a
solution of p-chloroacetophenone (0.772 g, 5.0 mmol) in THF
(10 mL) was added lithium alminum deuteride (0.215 g, 5.0 mmol)
in one portion. After refluxing for 13 h, the reaction mixture was
poured into water, and the solution was extracted with dichloro-
methane (30 mL) for three times. The combined extracts were
dried over magnesium sulfate, filtered, and concentrated to afford
1-p-chlorophenyl-1-deuteroethyl alcohol (1.00 g, 5.0 mmol) in
100% yield. This alcohol (0.157 g, 1.0 mmol) was treated with
triphenylphosphine (0.343 g, 1.0 mmol) and 47% HBr (0.194 g,
1.2 mmol) at 170 ꢂC for 2 h. The cooled reaction mixture was
recrystallized from 2-propanol to afford phosphonium bromide
D-2c (0.346 g, 0.85 mmol) in 85% yield. 1-(p-chlorophenyl)-1-
Synthesis of Salt 1f from o-Methylstyrene (3f). A mixture of
triphenylphosphine (0.68 g, 2.6 mmol) and hydrobromic acid
(48% in water, 0.34 mL, 2.0 mmol) was heated to 130 ꢂC for 5
min, and then o-methylstyrene (3f) (0.25 g, 2.1 mmol) was added.
The reaction mixture was heated to 270 ꢂC for 30 min. The reac-
tion mixture was cooled to rt and washed with hexane (5 mL ꢃ 3).
The remaining solid afforded glassy solid 2-(o-tolyl)ethyltriphen-
ylphosphonium bromide (1f). Salt 1f: glaasy solid. Salt 1f: hygro-
scopic glassy solid. 1H NMR (400 MHz, CDCl3): ꢀ 2.13 (s, 3H,
Me), 2.95–3.06 (m, 2H, CH2), 4.05–4.18 (m, 2H, CH2), 7.02–
7.29 (m, 4H, o-Tol), 7.65–7.93 (m, 15H, PPh3). 13C NMR (100
MHz, CDCl3): ꢀ 19.44 (Me), 23.83 (d, JPC ¼ 47 Hz, CH2), 25.32
(CH2), 117.79 (d, JPC ¼ 85 Hz, PPh3), 126.61 (o-Tol), 127.25
(o-Tol), 129.28 (o-Tol), 130.51 (o-Tol), 130.72 (d, JPC ¼ 12 Hz,
PPh3), 133.67 (d, JPC ¼ 10 Hz, PPh3), 135.37 (d, JPC ¼ 2 Hz,
PPh3), 135.57 (o-Tol), 136.44 (d, JPC ¼ 14 Hz, o-Tol). Salt 1f
was changed to the corresponding tetraphenylborate 7f: colorless
solid (0.87 g, 1.24 mmol), mp 169–171 ꢂC. 1H NMR (400 MHz,
CDCl3): ꢀ 2.05 (s, 3H, CH3), 2.75–2.89 (m, 4H, CH2), 6.76–
6.93 (m, 12H, BPh4 and o-Tol), 7.05–7.19 (m, 3H, o-Tol), 7.23–
7.36 (m, 15H, PPh3 and BPh4), 7.48–7.57 (m, 6H, PPh3), 7.70–
7.78 (m, 3H, PPh3). 13C NMR (100 MHz, CD3SOCD3): ꢀ 19.30
(CH3), 21.89 (d, JPC ¼ 47 Hz, CH2), 25.41 (d, JPC ¼ 3 Hz, CH2),
118.88 (d, JPC ¼ 85 Hz, PPh3), 122.27 (BPh4), 126.02 (BPh4),
126.88 (o-Tol), 127.69 (o-Tol), 129.49 (o-Tol), 130.94 (o-Tol),
130.94 (d, JPC ¼ 13 Hz, PPh3), 134.31 (d, JPC ¼ 10 Hz, PPh3),
135.67 (d, JPC ¼ 3 Hz, PPh3), 136.20 (BPh4), 136.35 (o-Tol),
137.86 (d, JPC ¼ 16 Hz, o-Tol), 164.01 (q, JBC ¼ 49 Hz, BPh4).
Anal. Calcd for C51H48BOP: C, 85.23; H, 6.73%. Found: C,
85.14; H, 6.55%.
1
deuteroethyl alcohol; H NMR (400 MHz, CDCl3) ꢀ 1.46 (s, 3H,
Me), 7.31 (s, 4H, Ar). 1-p-Chlorophenyl-1-deutero-ethylphospho-
nium bromide (1-D-2c); mp 230–232 ꢂC (lit.8 mp 230–232 ꢂC)
1H NMR (400 MHz, CDCl3): ꢀ 1.72 (d, 3H, JPH ¼ 35 Hz, Me),
7.12 (d, 2H, J ¼ 8 Hz, Ar), 7.20 (d, 2H, J ¼ 8 Hz, Ar), 7.60–7.93
(m, 15H, Ph).
Thermal Rearrangement of 1-D-2c. A mixture of Salt 1-D-
2c (0.242 g, 0.5 mmol) and triphenylphosphine (0.065 g, 0.25
mmol) was heated at 260 ꢂC for 30 min. The cooled reaction mix-
ture was dissolved in acetone (5 mL), which was added to a solu-
tion of sodium tetraphenylborate (0.171 g, 0.5 mmol) in acetone
(5 mL). The precipitates were removed by filtration, and the sol-
vent was evaporated to give pale brown oily crystals, which were
washed with ether (3 mL ꢃ 3) and recrystallized from acetone–
ether to afford colorless crystals of deuterated salt of 1c (0.180
1
g, 0.25 mmol). Mp 197–199 ꢂC. H NMR spectrum of deuterated
1c was identical to that of 1c except for the integral ratio of meth-
ylene signals. The NMR spectrum (in CDCl3) showed two meth-
ylenes at 4.26 and 3.05 in 58:42 ratio.
Salt 1g and 7g were obtained in a similar manner. Salt 1g:
hygroscopic glassy solid: 1H NMR (400 MHz, CDCl3): ꢀ 3.13–
3.22 (m, 2H, CH2), 4.05–4.18 (m, 2H, CH2), 7.10–7.25 (m, 2H,
o-ClC6H4), 7.30–7.55 (m, 2H, o-ClC6H4), 7.65–8.05 (m, 15H,
PPh3). 13C NMR (100 MHz, CDCl3): ꢀ 23.33 (d, JPC ¼ 48 Hz,
CH2), 26.05 (d, JPC ¼ 2 Hz, CH2), 117.67 (d, JPC ¼ 85 Hz, PPh3),
127.77 (ClC6H4), 128.86 (ClC6H4), 129.38 (ClC6H4), 130.72 (d,
JPC ¼ 13 Hz, PPh3), 131.91 (ClC6H4), 133.0 (ClC6H4), 133.78
(d, JPC ¼ 11 Hz, PPh3), 135.43 (d, JPC ¼ 3 Hz, PPh3), 135.71
(ClC6H4). Salt 7g: colorless solid. mp 157–159 ꢂC. 1H NMR
(400 MHz, CDCl3): ꢀ 2.75–2.92 (m, 4H, CH2CH2), 6.75–6.83
(m, 4H, BPh4), 6.85–6.91 (m, 9H, o-ClC6H4 + BPh4), 7.09 (t,
1H, J ¼ 7:6 Hz, o-ClC6H4), 7.19 (t, 1H, J ¼ 7:6 Hz, o-ClC6H4),
7.31–7.40 (m, 15H, BPh4, PPh3, and o-ClC6H4), 7.53–7.60
(m, 6H, PPh3), 7.73–7.80 (m, 3H, PPh3). 13C NMR (100 MHz,
CD3SOCD3): ꢀ 21.49 (d, JPC ¼ 49 Hz, CH2), 25.96 (CH2), 118.64
(d, JPC ¼ 85 Hz, PPh3), 122.26 (BPh4), 126.00 (BPh4), 128.24
Synthesis of p-(Chlorophenyl)ethene-2-13C (2-13C-3c). To a
solution of 13C-methyltriphenylphosphonium iodide (0.406 g, 1.0
mmol) and DBU (0.175 g, 1.1 mmol) in dichloromethane (10
mL) was added p-chlorobenzaldehyde (0.090 g, 0.6 mmol) in one-
portion. After refluxing for 12 h, the reaction mixture was washed
with water (5 mL ꢃ 3), separated, dried over magnesium sulfate,
and concentrated to afford a colorless oil. Chromatography on
silica gel by elution from hexane gave 2-13C-enriched 3c (p-
ClC6H4CH = 13CH2, 2-13C-3c) (0.067 g, 0.048 mmol). Colorless
oil: 1H NMR (400 MHz, CDCl3): ꢀ 5.27 (dd, 1H, J ¼ 11 Hz,
JCH ¼ 161 Hz, =CH2), 5.72 (dd, 1H, J ¼ 17 Hz, JCH ¼ 159 Hz,
=CH2), 6.66 (dd, 1H, J ¼ 11 and 17 Hz, =CH), 7.29 (d, 2H,
J ¼ 8 Hz, Ar), 7.32 (d, 2H, J ¼ 8 Hz, Ar). 13C NMR (100 MHz,
CDCl3) ꢀ 114.53 (=13CH2), 127.53 (Ar), 128.76 (Ar), 133.86
(Ar), 135.38 (=CHAr), 136.08 (Ar).
Reaction of p-Chloro-2-13C-styrene (2-13C-3C) with Tri-
phenylphosphonium Bromide.
To a mixture of triphenyl-
(ClC6H4), 129.68 (ClC6H4), 130.05 (ClC6H4), 130.96 (d, JPC
¼
phosphonium bromide and triphenylphosphine was added 2-13C-
3c (0.060 g, 0.43 mmol) at 130 ꢂC and the temperature was up to
265 ꢂC for 30 min. After the mixture was cooled to rt, the reaction
mixture was extracted with hexane and ether. In the 1H NMR
spectrum of the mixture, peaks for triphenylphosphine, 1-(p-
chlorophenyl)ethyl-2-13C-triphenylphosphonium bromide (2-13C-
2c), and 2-(p-chlorophenyl)ethyl-1-13C-triphenylphosphonium
bromide (1-13C-1c) were observed. 13C NMR clearly shows the
existence of 2-13C-2c (ꢀ 17.14) and 1-13C-1c (ꢀ 24.77) in almost
an 1:4 ratio. No peaks assigned to 1-p-chlorophenyl-1-13C-ethyl-
triphenylphosphonium bromide were observed.
12 Hz, PPh3), 131.48 (ClC6H4), 133.35 (ClC6H4), 134.30 (d,
JPC ¼ 10 Hz, PPh3), 135.74 (PPh3), 136.22 (BPh4), 136.93 (d,
JPC ¼ 16 Hz, ClC6H4), 164.10 (q, JBC ¼ 49 Hz, BPh4). Anal.
Calcd for C50H43BClP: C, 83.28; H, 6.01%. Found: C, 83.45;
H, 6.08%.
Thermolysis of 1-Indanyltriphenylphosphonium Bromide
(2i). Phosphonium bromide 2i (0.076 g, 0.17 mmol) was heated
at 275 ꢂC for 20 min. The reaction mixture was cooled to rt and
extracted with hexane (3 ꢃ 5 mL). The combined extracts were
concentrated to afford indene (0.013 g, 0.11 mmol), which was

1790 Bull. Chem. Soc. Jpn. Vol. 80, No. 9 (2007)
From Styrene to 2-Arylethylphosphonium Salts
B. Mennucci, M. Cossi, G. Scalmani, N. Rega, G. A. Petersson,
H. Nakatsuji, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J.
Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai,
M. Klene, X. Li, J. E. Knox, H. P. Hratchian, J. B. Cross, V.
Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E. Stratmann,
O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochterski,
P. Y. Ayala, K. Morokuma, G. A. Voth, P. Salvador, J. J.
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M. C. Strain, O. Farkas, D. K. Malick, A. D. Rabuck, K.
Raghavachari, J. B. Foresman, J. V. Ortiz, Q. Cui, A. G. Baboul,
S. Clifford, J. Cioslowski, B. B. Stefanov, G. Liu, A. Liashenko,
P. Piskorz, I. Komaromi, R. L. Martin, D. J. Fox, T. Keith,
M. A. Al-Laham, C. Y. Peng, A. Nanayakkara, M. Challacombe,
P. M. W. Gill, B. Johnson, W. Chen, M. W. Wong, C. Gonzalez,
J. A. Pople, Gaussian 03, Revision D.01, Gaussian, Inc.,
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