Br?nsted-acid-catalyzed coupling of electron-rich arenes with substituted allylic and secondary benzylic alcohols

Article abstract of DOI:10.1016/j.tet.2007.05.070

p-Toluenesulfonic acid and triflic acid catalyze efficiently the coupling of electron-rich arenes with allylic and benzylic alcohols. Reactions are conducted under mild conditions, in air, and in the absence of solvent.

Full text of DOI:10.1016/j.tet.2007.05.070

Tetrahedron 63 (2007) 7942–7948
Brønsted-acid-catalyzed coupling of electron-rich arenes with
substituted allylic and secondary benzylic alcohols
*
Jean Le Bras and Jacques Muzart
´
UMR 6519 ‘Reactions Selectives et Applications’, Boıte 44, CNRS-Universite de Reims Champagne-Ardenne,
´
ˆ
´
BP 1039, 51687 Reims Cedex 2, France
Received 16 February 2007; revised 27 April 2007; accepted 17 May 2007
Available online 24 May 2007
Abstract—p-Toluenesulfonic acid and triflic acid catalyze efficiently the coupling of electron-rich arenes with allylic and benzylic alcohols.
Reactions are conducted under mild conditions, in air, and in the absence of solvent.
Ó 2007 Elsevier Ltd. All rights reserved.
1. Introduction
alkylation of anilines with styrenes,15 acylation of aromatic
compounds,16 addition of 1,3-dicarbonyl compounds to
alkenes and alcohols,17 and nucleophilic substitution of
propargylic alcohols.18
Arenes and heteroarenes have proven to be quite attractive
targets because of the extensive use of these compounds in
the dyestuff, perfume, flavor, agriculture, and pharmaceuti-
cal industries. The coupling of allylic and benzylic groups
with arenes can be seen as electrophile–nucleophile combi-
nations, arenes being the nucleophiles and allylic or benzylic
compounds being the electrophiles. Mild methodologies
for such coupling include the Mo(II)-catalyzed allylic sub-
stitution of allylic alcohols or acetates with electron-rich
aromatics,1 the use of lanthanide and actinide triflates,2
cooperative catalysts in heterobimetallic regime,3 the Rh-
and Ir-catalyzed allylations of electron-rich arenes with
allylic tosylates,4 and heterogeneous catalysts.5
Direct arylation of allylic and benzylic alcohols under
conditions leading to water as the only by-product would
represent a green process. Surprisingly, such a simple
approach has not been described with electron-rich arenes,
probably because homogeneous Brønsted acids were not
found to be effective catalysts in Friedel–Crafts reactions,
in the past.19,20 However, while this work was in progress,
Sanz et al. have reported a similar procedure in organic me-
dium for the nucleophilic substitution of alcohols.21 Herein,
we report a parallel approach, which tolerates substrates that
were previously regarded as incompatible with strong
Brønsted acids.
Recently, a significant advance, due to Beller et al., has been
seen in the use of sub-stoichiometric amounts of transition-
metal compounds for arylation of benzylic alcohols and
carboxylates.6 Nevertheless, interest in metal-free and
solvent-free reactions is progressing because of both eco-
nomical concerns and increased environmental awareness.7
Therefore, Brønsted acids have received recent attention as
a simple alternative to toxic and precious metals, and the
formation of C–X bonds (X¼C, N, O, S) has been reported
by different groups. Various Brønsted acids have been found
to catalyze the addition of nitrogen and oxygen nucleophiles
to olefins.8 The formation of carbon–carbon bonds was
reported via the cyclization of siloxy alkynes,9 intermolecu-
lar Friedel–Crafts reactions using aliphatic alcohols,10 meth-
ylenecyclopropane,11 acetals,12 aldehydes13 and imines,14
2. Results and discussion
According to the literature, the alkylation of p-electron-rich
heteroaromatics, such as furans, by the standard Friedel–
Crafts approach was impractical because the Brønsted and
Lewis acid catalysts employed induced ring opening and
polymerization.19 While studying the arylation of (E)-4-phe-
nylbut-3-en-2-ol (1a) with 5 equiv of 2-methylfuran (2a),
we observed that Brønsted acids can be good catalysts under
mild conditions (Table 1). While no reaction occurred in
the presence of CH3CO2H (20 mol %) in dry CH2Cl2, a mix-
ture of 3aa and 4aa (3aa/4aa, 80/20) was obtained in 60%
yield with HCl as the catalyst (entries 1 and 2). Using
CF3CO2H instead of HCl increased the yield, especially
when the reaction was carried out without solvent (entries
3 and 4). Stronger acids shortened the reaction time to 1 h
Keywords: Brønsted acid; Friedel–Crafts; Solvent free; Green chemistry.
* Corresponding author. Tel.: +33 3 26 91 32 46; fax: +33 3 26 91 31 66;
e-mail: jean.lebras@univ-reims.fr
0040–4020/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2007.05.070

J. L. Bras, J. Muzart / Tetrahedron 63 (2007) 7942–7948
Table 1. Reaction of 2-methylfuran with (E)-4-phenylbut-3-en-2-ola
7943
and the best results were obtained with 5 mol % of triflic acid
(5) or monohydrated p-toluenesulfonic acid (6) (entries 6
and 7). The use of only a slight excess of 2a had little impact
on the yield (entry 8), but higher acid concentration led to
some decomposition (entry 9). The process was less efficient
with 1 mol % of acid (entry 10). Regioselectivity was close
to that observed in the Mo(II)-catalyzed coupling of 2a with
(E)-4-phenylbut-3-en-2-yl acetate.1b Indeed, the Brønsted
acid conditions led mainly to the formation of the C–C
bond between the 5-position of the furan ring and the methyl
terminus of the allyl moiety. Note that this reaction is not
sensitive to air or moisture and can be used with furan
derivatives, which is a rare feature of Friedel–Crafts-type
chemistry.6
O
OH
O
acid (cat)
50 °C
+
+
O
1a
2a
3aa 80/20
4aa
Entry Catalyst (mol %)
Solvent Time (h) Yield of 3aa+4aa (%)
1
2
3
4
5
6
CH3CO2H (20)
HCl (20)
CF3CO2H (20)
CF3CO2H (20)
H2SO4 (5)
CH2Cl2
CH2Cl2
CH2Cl2
8
8
8
8
1
1
1
2
1
2
0
60
82
87
83
87
87
80
75
61
CF3SO3H (5)
7
p-TolSO3H$H2O (5)
p-TolSO3H$H2O (5)
p-TolSO3H$H2O (20)
p-TolSO3H$H2O (1)
8b
9
We were interested in the reactivity of other alcohols and
arenes (Table 2). Triflic acid (5)22 and monohydrated p-
toluenesulfonic acid (6) were selected as catalysts. Allylic
alcohols, such as (E)-4-phenylbut-3-en-2-ol (1a), (E)-1,3-
diphenylprop-2-en-1-ol (1b), and cinnamyl alcohol (1c)
react with 2a, 1,3-dimethoxybenzene (2b), anisole (2c), and
10
a
Reaction conditions: 1a (1.0 mmol), 2a (5.0 mmol), solvent (0 or 1 mL),
50 ꢀC.
2a (1.1 mmol).
b
Table 2. Reactions of allylic and benzylic alcohols with arenesa
5 or 6 (5 mol%)
+
ROH
1
ArH
2
R-Ar
3,4
neat, 50 °C
OH
R1
OH
OMe
MeO
OMe
R3
O
R2
R1 = Me, 1a
R2 = H, R3 = Ph, 1d
2 = OMe, R3 = Me, 1e
2a
2b
2c
Ph, 1b
H, 1c
R
NH
O
NH
2d
2e
2f
Entry
1
2
Catalyst
t (h)
Product
Yield (%)
1
2
3
1a
1a
1a
1a
1a
1b
1b
1b
1b
1b
1b
1c
1c
1c
1c
1d
1d
1d
1d
1e
1e
1e
1e
1e
1e
2b
2c
2d
2e
2f
2a
2b
2c
2d
2e
2f
2a
2b
2c
2d
2a
2b
2c
2d
2a
2b
2c
2d
2e
2f
5
5
5
6
6
5
5
5
5
6
6
6
6
6
6
5
5
6
6
6
6
6
6
5
5
1
2
2
2
2
1
1
2
2
2
2
2
2
2
2
9
9
9
9
2
2
2
2
2
2
3ab/4ab (85/15)
3ac
3ad/4ad (95/5)
3ae/4ae (45/55)
3af/4af (75/25)
3ba
3bb
3bc
86
80
80
55
62
95
80
83
85
95
83
71
70
73d
64
90
70
92
86
81
78
68
87
66
69
4b,c
5
6
7
8
9
3bd
3be
10b,c
11
12b
13
14
15
16
17
18
19
20b
21
22
23
24b,c
25
3bf
3ca/4ca (75/25)
3cb/4cb (90/10)
3cc
3cd
3da
3db
3dc
3dd
3ea
3eb
3ec
3ed
3ee
3ef
a
Reaction conditions: alcohol (1.0 mmol), arene (5.0 mmol), catalyst (0.05 mmol), 50 ꢀC.
Performed in dry CH2Cl2 (1 mL).
Performed with 1.0 equiv of arene.
b
c
d
Isolated with traces of a by-product corresponding probably to 1-cinnamyl-2-methoxybenzene.

7944
J. L. Bras, J. Muzart / Tetrahedron 63 (2007) 7942–7948
benzofuran (2d) in good to excellent yields and short reac-
tion times. The reaction of 2a, 2b, and 2d with 1a and 1c
exhibited good to high regioselectivity at the less hindered
terminus of the allylic moiety (entries 1, 3, 12, 13, and
15). In all cases, the trans-configuration of the double bond
was preserved. Arenes were alkylated regioselectively as ob-
served in other processes (Scheme 1).23 Note that 2c reacted
with 1a with high selectivity through the p-position of the
aromatic ring at the methyl terminus of the allyl moiety
(entry 2). Indole (2e) and pyrrole (2f) also react with 1a and
1b in moderate to excellent yields (entries 4, 5, 10, and 11),
with regioselectivity similar to that observed in other pro-
cesses (Scheme 1),24 but no reaction was observed with 1c.
Benzylicalcoholssuchasbenzhydrol(1d)and1-(4-methoxy-
phenyl)ethanol (1e) also reacted with arenes 2a–d (entries
16–23) and anisole (2c) affording solely the p-isomers 3dc
and 3ec. Compound 1d gave no reaction with indole (2e)
and pyrrole (2f) while 1e reacted in fair yields (entries 24
and 25).
The reaction is operationally simple and can be performed
in the absence of solvents. Of special interest are the para-
selectivity observed with anisole and the tolerance of furans,
indole, and pyrrole usually classified as ‘acid-sensitive’
compounds. This metal-free and solvent-free method, which
gives water as the only side product, represents a clean and
environmental friendly alternative to the already established
use of metallic catalysts.
4. Experimental section
4.1. General information
All reagents used were commercially available and of high
purity grade. Allylic and benzylic alcohols were obtained
by reduction of ketones with NaBH4 in MeOH. CH2Cl2
was distilled over CaH2 under argon. Column chromato-
graphy was conducted over silica gel of 40–63 mm. NMR
spectroscopy was performed with a 250 MHz apparatus in
CDCl3 and referenced to TMS.
OMe
MeO
OMe
4.2. General procedure
O
A 50 mL round-bottomed flask was charged with alcohol
(1.0 mmol), arene (5.0 mmol) and, in some cases, solvent
(1 mL). The acid (0.05 mmol) was added at room tempera-
ture (PTSA$H2O) or at 0 ꢀC (CF3SO3H). The mixture was
heated (oil bath, 50 ꢀC) for the appropriate time. After cool-
ing to room temperature, saturated NaHCO3 solution (5 mL)
was added and the mixture was extracted with Et2O (5ꢁ
5 mL). The organic phase was dried over MgSO4, filtered,
and concentrated under reduced pressure. The excess of
arene was removed by distillation and the product was puri-
fied by column chromatography on silica gel (petroleum
ether/ethyl acetate 98/2, then petroleum ether/ethyl acetate
95/5).
2a
2b
2c
NH
O
NH
2d
2e
2f
Scheme 1. Regioselectivities observed with 2.
Scheme 2 shows plausible pathways for the reaction. We
have observed the formation of bis(diphenylmethyl) ether
(7d) during the reaction of 1d with 2a. Reaction of 7d
with 2a in the presence of 5 required 8 h to afford 3da in
95%. The coupling probably proceeds through the formation
of a stabilized carbocation, which can react with 2 to pro-
duce 3 and 4, or with 1 to give ether 7. The latter can regen-
erate the carbocation and 1 via acid catalysis. The similar
reactivity of 1d and 7d and the longer reaction time observed
compared to the other examples indicate that the stability of
7d slows down the reaction, probably via steric effects. The
absence of reactivity of 1d with 2e and 2f also shows that
other factors affect the efficiency of the process.
Caution: addition of triflic acid to 2-methylfuran gives a vio-
lent reaction. The following procedure should be used:
4.3. Typical procedure with triflic acid and 2-methyl-
furan
A 50 mL round-bottomed flask was charged with alcohol
(1.0 mmol) and CH2Cl2 (1 mL) if required and cooled
with an ice water bath. CF3SO3H (0.05 mmol, 4.0 mL) was
added dropwise in order to prevent the accumulation of
a colored gum, followed by the arene (5.0 mmol). The
mixture was heated (oil bath, 50 ꢀC) for the appropriate
time. The work-up was carried out as for the above general
procedure.
H2O
R+
ROH
1
ROH H+
H+
ROR
7
1
ArH
RAr
3, 4
2
4.3.1. (E)-1-Phenyl-3-(2-methylfuran-5-yl)-1-butene
(3aa) and (E)-4-phenyl-4-(2-methylfuran-5-yl)-2-butene
(4aa).1b Colorless oil. Compound 3aa: 1H NMR (measured
in a mixture with 4aa): d¼1.33 (d, J¼7.0 Hz, 3H, CH3CH),
2.18 (s, 3H, CH3-furan), 3.55 (quint, J¼7.0 Hz, 1H,
CHCH3), 5.80–5.84 (m, 2H, ]CH-furan), 6.20 (dd, J¼
15.9 Hz, J¼7.2 Hz, 1H, CH]CH–CH), 6.36 (d, J¼
15.9 Hz, 1H, ArCH]CH), 7.05–7.35 (m, 5H, Ar). Com-
Scheme 2. Plausible pathways for the acid-catalyzed reaction.
3. Conclusion
In summary, we have shown that p-toluenesulfonic acid and
triflic acid are efficient catalysts for the direct coupling of
phenyl-substituted allylic alcohols and secondary benzylic
alcohols with electron-rich arenes under mild conditions.
1
pound 4aa: H NMR (measured in a mixture with 3aa):
d¼1.63 (ddd, J¼6.4 Hz, J¼1.5 Hz, J¼0.9 Hz, 3H,

J. L. Bras, J. Muzart / Tetrahedron 63 (2007) 7942–7948
7945
CH3CH]CH), 2.15 (s, 3H, CH3-furan), 4.53 (d, J¼7.5 Hz,
1H, ArCH), 5.41 (dqd, J¼12.9 Hz, J¼6.4 Hz, J¼1.1 Hz,
CH]CHCH3), 5.75–5.84 (m, 1H, CHCH]CH), 5.85–
5.93 (m, 2H, ]CH-furan), 7.05–7.35 (m, 5H, Ar).
CH]CHCH3), 6.74–6.78 (m, 1H, CH–NH), 6.94–7.40 (m,
8H, Ar), 7.66 (d, J¼7.8 Hz, 1H, Ar), 7.73 (br s, 1H, NH).
4.3.6. (E)-1-Phenyl-3-(pyrrol-2-yl)-1-butene (3af) and
(E)-4-phenyl-(pyrrol-3-yl)-2-butene (4af). Pale yellow
oil. Compound 3af: H NMR (measured in a mixture with
1
4.3.2. (E)-1-Phenyl-3-(2,4-dimethoxyphenyl)-1-butene
(3ab) and (E)-4-phenyl-4-(2,4-dimethoxyphenyl)-2-bu-
tene (4ab). Pale yellow oil. Compound 3ab: 1H NMR (mea-
sured in a mixture with 4ab): d¼1.38 (d, J¼7.0 Hz, 3H,
CH3CH), 3.72 (s, 3H, OCH3), 3.75 (s, 3H, OCH3), 3.92–
4.06 (m, 1H, CHCH3), 6.32–6.47 (m, 4H, CH]CH, Ar),
7.00–7.34 (m, 6H, Ar). 13C NMR (measured in a mixture
with 4ab): d¼20.2, 34.8, 55.3, 55.4, 98.8, 104.2, 126.2,
126.6, 126.9, 127.9, 128.0, 128.5, 135.3, 138.0, 157.8,
4af): d¼1.40 (d, J¼6.9 Hz, 3H, CH3CH), 3.58 (quint, J¼
6.9 Hz, 1H, CHCH3), 5.93–5.98 (m, 1H, CH-pyrrole), 6.05–
6.13 (m, 1H, CH-pyrrole), 6.19 (dd, J¼15.8 Hz, J¼7.8 Hz,
CH]CH–CH), 6.40 (d, J¼15.9 Hz, ArCH]CH), 6.58–
6.68 (m, 1H, CH-pyrrole), 7.10–7.34 (m, 5H, Ar), 7.92 (br
s, 1H, NH). 13C NMR (measured in a mixture with 4af): d¼
19.7, 36.3, 104.3, 108.4, 117.0, 126.3, 127.5, 128.4, 128.6,
1
128.7, 129.5, 133.9. Compound 4af: H NMR (measured
1
159.3. Compound 4ab: H NMR (measured in a mixture
in a mixture with 3af): d¼1.65 (ddd, J¼6.4 Hz, J¼1.5 Hz,
J¼0.7 Hz, 3H, CH3CH), 4.56 (d, J¼7.7 Hz, 1H, ArCH),
5.46 (dqd, J¼15.0 Hz, J¼6.4 Hz, J¼1.0 Hz, CHCH]CH),
5.71–5.85 (m, 2H, CH]CHCH3, CH-pyrrole), 6.05–6.13
(m, 1H, CH-pyrrole), 6.58–6.68 (m, 1H, CH-pyrrole), 7.10–
7.34 (m, 5H, Ar) 7.75 (br s, 1H, NH). IR (3af/4af, film):
n¼3432, 3025, 2967, 2930, 1561, 1493, 1449, 1115, 1093,
1207, 967 cmꢂ1. GC–MS (EI): tR (4af)¼8.5; m/z (%)¼
197 (94) [M+], 182 (42), 156 (58), 128 (74), 115 (100); tR
(3af)¼9.3; m/z (%)¼197 (94) [M+], 182 (80), 115 (100).
ESHRMS: calcd for C14H16N: 198.1283. Found: 198.1275.
with 3ab): d¼1.69 (dd, J¼6.4 Hz, J¼0.9 Hz, 3H, CH3CH),
3.65 (s, 3H, OCH3), 3.75 (s, 3H, OCH3), 5.00 (d,
J¼7.0 Hz, 1H, ArCH), 5.25–5.45 (m, 1H, CH]CHCH3),
5.80–5.95 (m, 1H, CHCH]CH), 6.32–6.47 (m, 2H, Ar),
7.00–7.34 (m, 6H, Ar). IR (3ab/4ab, film): n¼3024, 2998,
2960, 2834, 1612, 1587, 1504, 1465, 1293, 1260, 1208,
1179, 1157, 1133, 1037, 968 cmꢂ1. GC–MS (EI): tR (4ab)¼
10.8; m/z (%)¼268 (94) [M+], 253 (74), 237 (46), 207 (55),
129 (63), 115 (100); tR (3ab)¼11.9; m/z (%)¼268 (40) [M+],
253 (100), 237 (24), 115 (54). ESHRMS: calcd for
C18H21O2: 269.1542. Found: 269.1546.
4.3.7. 5-((E)-1,3-Diphenylallyl)-2-methylfuran (3ba). Pale
1
4.3.3. (E)-1-Phenyl-3-(4-methoxyphenyl)-1-butene
yellow oil. H NMR: d¼2.24 (s, 3H, CH3), 4.84 (d, J¼
1
(3ac).1b Colorless oil. H NMR: d¼1.35 (d, J¼7.0 Hz, 3H,
7.2 Hz, 1H, CH]CHCHAr), 5.88–5.99 (m, 2H, ]CH-
furan), 6.38 (d, J¼15.9 Hz, 1H, ArCH]CH), 6.56 (dd,
J¼15.9 Hz, J¼7.2 Hz, 1H, ArCH]CHCH), 7.16–7.40 (m,
10H, Ar). 13C NMR: d¼13.7, 48.6, 106.2, 107.6, 126.5,
126.9, 127.5, 128.4, 128.6, 128.7, 130.2, 131.5, 137.2,
141.5, 151.5, 154.4. IR (pellets): n¼3025, 2885, 1598,
1556, 1494, 1450, 1216, 1154, 1027, 961 cmꢂ1. GC–MS
(EI): tR¼11.7; m/z (%)¼274 (80) [M+], 231 (48), 215 (42),
192 (78), 115 (100). Anal. Calcd for C20H18O: C, 87.56;
H, 6.61; Found: C, 87.75; H, 6.68.
CH3), 3.44–3.57 (m, 1H, CHCH3), 3.69 (s, 3H, OCH3),
6.26–6.30 (m, 2H, ArCH]CH), 6.73–6.80 (m, 2H, Ar),
7.05–7.30 (m, 7H, Ar).
4.3.4. (E)-1-Phenyl-3-(benzofuran-2-yl)-1-butene (3ad)
and (E)-4-phenyl-(benzofuran-2-yl)-2-butene (4ad). Pale
yellow gum. Compound 3ad: 1H NMR (measured in a mix-
ture with 4ad): d¼1.63 (d, J¼7.0 Hz, 3H, CH3), 3.91 (quint,
J¼7.0 Hz, 1H, CHCH3), 6.45 (dd, J¼15.9 Hz, J¼7.1 Hz,
1H, ArCH]CH), 6.52–6.55 (m, 1H, O–C]CH), 6.61 (d,
J¼15.9 Hz, ArCH]CH), 7.20–7.62 (m, 9H, Ar). 13C
NMR (measured in a mixture with 4ad): d¼19.0, 37.2,
101.5, 111.1, 120.6, 122.7, 123.5, 126.4, 127.5, 128.7, 128.9,
130.5, 131.3, 137.3, 154.9, 161.7. Compound 4ad: 1H NMR
(selected data measured in a mixture with 3ad): d¼1.80–
1.86 (m, 3H, CH3), 4.88 (d, J¼7.2 Hz, 1H, ArCH), 5.58–
5.74 (m, 1H, CHCH3), 5.90–6.06 (m, 1H, CH]CHCH3).
IR (3ad/4ad, pellets): n¼3026, 2967, 2930, 1580, 1493,
4.3.8. 1-((E)-1,3-Diphenyl-2-propenyl)-2,4-dimethoxy-
1
benzene (3bb). Pale yellow oil. H NMR: d¼3.75 (s, 3H,
OCH3), 3.80 (s, 3H, OCH3), 5.22 (d, J¼7.1 Hz, 1H, CH]
CHCHAr), 6.25 (d, J¼15.9 Hz, 1H, ArCH]CH), 6.42–6.50
(m, 2H, Ar), 6.66 (dd, J¼15.9 Hz, J¼7.0 Hz, 1H, ArCH]
CHCH), 7.07 (d, J¼8.9 Hz, 1H, Ar), 7.15–7.40 (m, 10H,
Ar). 13C NMR: d¼46.6, 55.4, 55.6, 99.0, 104.2, 124.5, 126.2,
126.4, 127.2, 128.3, 128.6, 128.7, 130.0, 130.9, 132.9, 137.7,
143.9, 158.0, 159.6. IR (pellets): n¼3024, 2999, 2934, 2833,
1610, 1586, 1503, 1451, 1292, 1260, 1207, 1176, 1156, 1116,
1035, 969 cmꢂ1. GC–MS (EI): tR¼18.8; m/z (%)¼330 (10)
[M+], 192 (28), 165 (44), 115 (48), 91 (77), 77 (100).
ESHRMS: calcd for C23H23O2: 331.1698. Found: 331.1701.
1453, 1296, 1254, 1168, 1103, 1033, 1010, 966, 943 cmꢂ1
.
GC–MS (EI): tR (4ad)¼10.4; m/z (%)¼248 (80) [M+], 233
(100), 115 (77); tR (3ad)¼11.3; m/z (%)¼248 (98) [M+],
233 (100), 115 (97). Anal. Calcd for C18H16O: C, 87.06;
H, 6.49; Found: C, 86.65; H, 6.63.
4.3.5. (E)-1-Phenyl-3-(indol-3-yl)-1-butene (3ae) and (E)-
4-phenyl-(indol-3-yl)-2-butene (4ae).1b Pale yellow gum.
Compound 3ae: 1H NMR (measured in a mixture with
4ae): d¼1.54 (d, J¼7.0 Hz, 3H, CH3), 3.90 (quint,
J¼7.0 Hz, 1H, CHCH3), 6.42–6.48 (m, 2H, ArCH]CH),
6.87–6.91 (m, 1H, CH–NH), 6.94–7.40 (m, 9H, Ar), 7.73
4.3.9. 1-((E)-1,3-Diphenyl-2-propenyl)-4-methoxy-benz-
ene (3bc).25 Pale yellow oil. 1H NMR: d¼3.79 (s, 3H,
OCH3), 4.95 (d, J¼7.3 Hz, 1H, CH]CHCHAr), 6.46 (d,
J¼15.8 Hz, 1H, ArCH]CH), 6.80 (dd, J¼15.8 Hz, J¼
7.4 Hz, 1H, ArCH]CHCH), 6.94–7.00 (m, 2H, Ar), 7.22–
7.50 (m, 12H).
1
(br s, 1H, NH). Compound 4ae: H NMR (measured in a
mixture with 3ae): d¼1.67–1.73 (m, 3H, CH3), 4.87 (d,
J¼7.5 Hz, 1H, ArCH), 5.50 (dq, J¼15.1 Hz, J¼6.3 Hz,
1H, CHCH3), 5.93 (dd, J¼15.1 Hz, J¼7.6 Hz, 1H,
4.3.10. 2-((E)-1,3-Diphenyl-2-propenyl)benzofuran (3bd).
White solid, mp 85–87 ꢀC. 1H NMR: d¼4.96 (d, J¼7.3 Hz,
1H, CH]CHCHAr), 6.34–6.46 (m, 2H, ArCH]CH,

7946
J. L. Bras, J. Muzart / Tetrahedron 63 (2007) 7942–7948
O–C]CH), 6.58 (dd, J¼15.8 Hz, J¼7.3 Hz, ArCH]CH),
7.10–7.46 (m, 14H, Ar). 13C NMR: d¼48.8, 104.2, 111.3,
120.8, 122.8, 123.8, 126.6, 127.3, 127.8, 128.5, 128.7 (2C),
128.8, 129.1, 132.4, 137.0, 140.5, 155.2, 159.4. IR (pellets):
n¼3080, 3028, 3022, 2924, 2875, 2850, 1568, 1579, 1490,
1453, 1254, 1163, 1070, 972, 960 cmꢂ1. GC–MS (EI):
tR¼18.3; m/z (%)¼310 (32) [M+], 231 (42), 202 (42), 178
(72), 115 (60), 77 (100). Anal. Calcd for (C23H18O): C,
89.00; H, 5.85; Found: C, 88.59; H, 5.87.
(100). ESHRMS: calcd for C17H19O2: 255.1285. Found:
255.1383.
4.3.15. (E)-1-Phenyl-3-(4-methoxyphenyl)-1-propene
1
(3cc).1b Colorless oil. H NMR: d¼3.47 (d, J¼5.9 Hz, 2H,
CH]CHCH2Ar), 3.77 (s, 3H, OCH3), 6.24–6.48 (m, 2H,
ArCH]CH), 6.84 (d, J¼8.3 Hz, 2H, Ar), 7.10–7.40 (m,
7H, Ar).
4.3.16. (E)-1-Phenyl-3-(benzofuran-2-yl)-1-propene
(3cd). Pale yellow oil. 1H NMR: d¼3.70 (d, J¼6.7 Hz,
2H, CH]CHCH2Ar), 6.33 (dt, J¼15.8 Hz, J¼6.7 Hz,
ArCH]CH), 6.39–6.43 (m, 1H, O–C]CH), 6.52 (d, J¼
15.9 Hz, ArCH]CH), 7.08–7.50 (m, 9H, Ar). 13C NMR:
d¼32.3, 102.9, 111.0, 120.6, 122.7, 123.6, 124.7, 126.4,
127.6, 128.7, 129.0, 132.8, 137.2, 155.0, 157.2. IR (film): n¼
GC–MS (EI): tR¼11.1; m/z (%)¼234 (100) [M+], 157 (30),
131 (45), 128 (67), 115 (52), 102 (30), 77 (57). Anal. Calcd
for (C17H14O): C, 87.15; H, 6.02; Found: C, 87.33; H, 6.14.
4.3.11. 3-((E)-1,3-Diphenyl-2-propenyl)-1H-indole
1
(3be).26 Pale yellow oil. H NMR: d¼5.11 (d, J¼7.3 Hz,
1H, CH]CHCHAr), 6.43 (d, J¼15.9 Hz, 1H, ArCH]CH),
6.72 (dd, J¼15.8 Hz, J¼7.3 Hz, ArCH]CHCH), 6.86–6.89
(m, 1H, CH–NH), 6.96–7.06 (m, 1H, Ar), 7.10–7.46 (m,
13H, Ar), 7.97 (br s, 1H, NH).
3058, 3028, 1598, 1495, 1454, 1422, 1253, 1163, 965 cmꢂ1
.
4.3.12. 2-((E)-1,3-Diphenyl-2-propenyl)-1H-pyrrole
1
(3bf). White solid, mp 71–73 ꢀC. H NMR: d¼4.86 (d,
J¼7.5 Hz, 1H, CH]CHCHAr), 5.94–5.99 (m, 1H, CH-
pyrrole), 6.17 (m, 1H, CH-pyrrole), 6.42 (d, J¼15.8 Hz,
1H, ArCH]CH), 6.59 (dd, J¼15.8 Hz, J¼7.5 Hz, ArCH]
CHCH), 6.67–6.72 (m, 1H, CH-pyrrole), 7.16–7.40 (m,
10H, Ar), 7.85 (br s, 1H, NH). 13C NMR: d¼48.1, 106.8,
108.4, 117.4, 126.5, 127.0, 127.6, 128.5, 128.7, 128.8, 131.3,
133.0, 137.1, 142.3. IR (pellets): n¼3386, 3083, 3058, 3029,
1599, 1552, 1491, 1449, 1415, 1396, 1271, 1200, 1112, 1095,
1062, 1027, 977, 959 cmꢂ1. GC–MS (EI): tR¼12.7; m/z
(%)¼259 (95) [M+], 180 (67), 115 (100), 77 (98). ESHRMS:
calcd for C19H18N: 260.1447. Found: 259.1439.
4.3.17. 2-Benzhydryl-5-methylfuran (3da).23b Colorless
1
oil. H NMR: d¼2.23 (s, 3H, CH3), 5.43 (s, 1H, ArCH),
5.78 (d, J¼3.0 Hz, 1H, ]CH-furan), 5.88 (d, J¼3.0 Hz,
1H, ]CH-furan), 7.12–7.42 (m, 10H, Ar).
4.3.18. 1-((2,4-Dimethoxyphenyl)diphenylmethane
1
(3db). White solid, mp 120–124 ꢀC. H NMR: d¼3.60 (s,
3H, OCH3), 3.70 (s, 3H, OCH3), 5.83 (s, 1H, ArCH), 6.35
(dd, J¼8.4 Hz, J¼2.4 Hz, 1H, Ar), 6.43 (d, J¼2.3 Hz, 1H,
Ar), 6.73 (d, J¼8.4 Hz, 1H, Ar), 7.00–7.38 (m, 10H, Ar).
13C NMR: d¼49.3, 55.3, 55.6, 98.7, 103.8, 125.3, 126.1,
128.2, 129.5, 130.9, 144.3, 158.1, 159.5. IR (pellets):
n¼3056, 2951, 2830, 1611, 1585, 1501, 1467, 1451, 1290,
1259, 1207, 1117, 1045, 835 cmꢂ1. GC–MS (EI): tR¼13.5;
m/z (%)¼304 (100) [M+], 289 (25), 273 (22), 227 (73),
165 (53), 91 (100). ESHRMS: calcd for C21H21O2:
305.1542. Found: 305.1540.
4.3.13. (E)-1-Phenyl-3-(2-methylfuran-5-yl)-1-propene
(3ca) and 3-phenyl-3-(2-methylfuran-5-yl)-1-propene
(4ca).1b Colorless oil. Compound 3ca: 1H NMR (measured
in a mixture with 4ca): d¼2.17 (s, 3H, CH3), 3.41 (d,
J¼6.5 Hz, 2H, CH]CHCH2), 5.64–5.88 (m, 2H, ]CH-
furan), 6.00–6.28 (m, 1H, ArCH]CHCH2), 6.40 (d,
J¼15.8 Hz, 1H, ArCH]CH), 7.02–7.32 (m, 5H, Ar). Com-
1
pound 4ca: H NMR (measured in a mixture with 3ca):
d¼2.15 (s, 3H, CH3), 4.59 (d, J¼7.0 Hz, 1H, ArCHCH]
CH2), 4.95 (td, J¼17.0 Hz, J¼1.4 Hz, 1H, CH]CH2),
5.09 (td, J¼10.1 Hz, J¼1.4 Hz, 1H, CH]CH2), 5.64–5.88
(m, 2H, ]CH-furan), 6.00–6.28 (m, 1H, ArCHCH]CH2),
7.02–7.32 (m, 5H, Ar).
4.3.19. 1-((4-Methoxyphenyl)diphenylmethane (3dc).28
White solid, mp 55–57 ꢀC. 1H NMR: d¼3.74 (s, 3H,
OCH3), 5.49 (s, 1H, ArCH), 6.77–6.85 (m, 2H, Ar), 6.98–
7.32 (m, 12H, Ar).
4.3.20. 2-Benzhydrylbenzofuran (3dd). White solid, mp
1
4.3.14. (E)-1-Phenyl-3-(2,4-dimethoxyphenyl)-1-propene
(3cb) and 3-phenyl-3-(2,4-dimethoxyphenyl)-1-propene
(4cb).27 Colorless oil. Compound 3cb: 1H NMR (measured
in a mixture with 4cb): d¼3.45 (d, J¼5.0 Hz, 2H, CH]
CHCH2Ar), 3.76 (s, 3H, OCH3), 3.78 (s, 3H, OCH3), 6.30–
6.48 (m, 3H, ArCH]CH, Ar), 7.00–7.40 (m, 6H, Ar). 13C
NMR (measured in a mixture with 4cb): d¼32.9, 55.3,
55.4, 98.6, 104.0, 121.0, 126.1, 126.9, 128.5, 129.4, 130.2,
130.4, 137.9, 158.2, 159.5. Compound 4cb: 1H NMR (mea-
sured in a mixture with 3ca): d¼3.70 (s, 3H, OCH3), 3.80
(s, 3H, OCH3), 4.82–2.96 (m, 1H, CH]CH2), 5.06 (d,
J¼6.6 Hz, 1H, ArCHCH]CH2), 5.12–5.20 (m, 1H,
CH¼CH2), 6.30–6.48 (m, 3H, ArCHCH]CH2, Ar), 7.00–
7.40 (m, 6H, Ar). IR (3cb/4cb, film): n¼3025, 2936, 2834,
1614, 1588, 1505, 1465, 1291, 1208, 1156, 1038,
967 cmꢂ1. GC–MS (EI): tR (4cb)¼10.2; m/z (%)¼254 (15)
[M+], 138 (62), 115 (88), 91 (76), 77 (100); tR (3cb)¼11.6;
m/z (%)¼254 (100) [M+], 223 (48), 178 (40), 138 (44), 115
110–114 ꢀC. H NMR: d¼5.85 (s, 1H, ArCH), 6.54 (s, O–
C]CH), 7.36–7.86 (m, 14H, Ar). 13C NMR: d¼51.5, 105.8,
111.3, 120.8, 122.8, 123.9, 127.1, 128.6, 128.7, 129.0, 141.2,
155.2, 160.0. IR (pellets): n¼3064, 3027, 1598, 1582, 1494,
1451, 1252, 1163, 1148, 1130, 1104, 1079, 1029, 1004,
957 cmꢂ1. GC–MS (EI): tR¼12.3; m/z (%)¼284 (17)
[M+], 207 (62), 178 (90), 77 (100). Anal. Calcd for
(C21H16O): C, 88.70; H, 5.67; Found: C, 88.60; H, 5.77.
4.3.21. 2-(1-(4-Methoxyphenyl)ethyl)-5-methylfuran
(3ea).23b Pale yellow oil. H NMR: d¼1.53 (d, J¼7.2 Hz,
1
3H, ArCHCH3), 2.21 (s, 3H, CH3-furan), 3.76 (s, 3H,
OCH3), 4.01 (q, J¼7.1 Hz, ArCHCH3), 5.85–5.87 (m, 2H,
]CH-furan), 6.83 (d, J¼8.7 Hz, 2H, Ar), 7.13 (d,
J¼8.7 Hz, 2H, Ar).
4.3.22. 1-Methoxy-4-(1-(2,4-dimethoxyphenyl)ethyl)-
benzene (3eb).29 Colorless oil. 1H NMR: d¼1.52 (d,

J. L. Bras, J. Muzart / Tetrahedron 63 (2007) 7942–7948
7947
ꢁ
Davis, S. L.; Baxendale, I. R.; Mitchell, W. L.; Kocovsky, P.
J. Org. Chem. 1999, 64, 2751–2764; (c) Malkov, A. V.;
ꢂ
J¼7.2 Hz, 3H, CHCH3), 3.75 (s, 3H, OCH3), 3.76 (s, 3H,
OCH3), 3.77 (s, 3H, OCH3), 4.43 (q, J¼7.2 Hz, 1H,
CHCH3), 6.39–6.46 (m, 2H, Ar), 6.80 (d, J¼8.3 Hz, 2H,
Ar), 7.01 (d, J¼9.1 Hz, 1H, Ar), 7.14 (d, J¼8.3 Hz, 2H, Ar).
ꢁ
Spoor, P.; Vinader, V.; Kocovsky, P. J. Org. Chem. 1999, 64,
ꢂ
5308–5311.
2. (a) Noji, M.; Ohno, T.; Fuji, K.; Futaba, N.; Tajima, H.; Ishii, K.
J. Org. Chem. 2003, 68, 9340–9347; (b) Shiina, I.; Suzuki, M.
Tetrahedron Lett. 2002, 43, 6391–6394; (c) Kotsuki, H.; Oshisi,
T.; Inoue, M. Synlett 1998, 255–256; (d) Tsuchimoto, T.;
Tobita, K.; Hiyama, T.; Fukuzawa, S.-I. J. Org. Chem. 1997,
62, 6997–7005.
4.3.23. 1,1-Bis(4-methoxyphenyl)ethane (3ec).30 White
1
solid, mp 67–69 ꢀC. H NMR: d¼1.58 (d, J¼7.1 Hz, 3H,
CHCH3), 3.77 (s, 6H, OCH3), 4.06 (q, J¼7.1 Hz, 1H,
CHCH3), 6.82 (d, J¼8.7 Hz, 4H, Ar), 7.12 (d, J¼8.7 Hz,
4H, Ar).
3. Choudhury, J.; Podder, S.; Roy, S. J. Am. Chem. Soc. 2005, 127,
6162–6163.
4. Tsukada, N.; Yagura, Y.; Sato, T.; Inoue, Y. Synlett 2003,
1431–1434.
5. Selected recent examples: (a) Okumura, K.; Yamashita, K.;
4.3.24. 2-(1-(4-Methoxyphenyl)ethyl)benzofuran (3ed).
White solid, mp 43–45 ꢀC. 1H NMR: d¼1.66 (d, J¼7.2 Hz,
3H, CHCH3), 3.73 (s, 3H, OCH3), 4.19 (q, J¼7.1 Hz, 1H,
CHCH3), 6.37–6.41 (m, 1H, O–C]CH), 6.85 (d,
J¼8.7 Hz, 2H, Ar), 7.14–7.24 (m, 4H, Ar), 7.36–7.52 (m,
2H, Ar). 13C NMR: d¼20.6, 38.9, 55.3, 102.0, 111.1,
114.1, 120.6, 122.6, 123.5, 128.6, 128.8, 135.5, 155.0, 158.5,
162.6. IR (film): n¼2965, 2933, 2835, 1610, 1584, 1512,
1454, 1377, 1299, 1265, 1248, 1175, 1147, 1108, 1069,
1057, 1031, 1009, 934 cmꢂ1. GC–MS (EI): tR¼11.1; m/z
(%)¼252 (35) [M+], 237 (100), 165 (30). Anal. Calcd for
(C17H16O2): C, 80.93; H, 6.39; Found: C, 80.71; H, 6.41.
ꢂ
Hirano, M.; Niwa, M. J. Catal. 2005, 234, 300–307; (b) Rac,
ꢂ
ꢂ
ꢂ
ꢂ
B.; Mulas, G.; Csongradi, A.; Loki, K.; Molnar, A. Appl.
Catal. 2005, 282, 255–265; (c) Mantri, K.; Komura, K.;
Kubota, Y.; Sugi, Y. J. Mol. Catal. A: Chem. 2005, 236, 168–
175; (d) Macquarrie, D. J.; Tavener, S. J.; Harmer, M. A.
Chem. Commun. 2005, 2363–2365; (e) Salavati-Niasari, M.;
Hasanalian, J.; Najafian, H. J. Mol. Catal. A: Chem. 2004,
209, 209–214; (f) Shrigadi, N. B.; Shinde, A. B.; Samant,
S. D. Appl. Catal. 2003, 252, 23–35; (g) Hu, X.; Chuah,
G. K.; Jaenicke, S. Appl. Catal. 2001, 217, 1–9; (h)
Choudary, V. R.; Jana, S. K. J. Catal. 2001, 201, 225–235; (i)
Deshpande, A. B.; Bajpai, A. R.; Samant, S. D. Appl. Catal.
2001, 209, 229–235; (j) Smith, K.; Pollaud, G. M.; Matthews, I.
Green Chem. 1999, 1, 75–81.
4.3.25. 3-(1-(4-Methoxyphenyl)ethyl)-1H-indole (3ee).
White solid, mp 137–140 ꢀC. 1H NMR: d¼1.67 (d,
J¼7.1 Hz, 3H, CHCH3), 3.76 (s, 3H, OCH3), 4.32 (q,
J¼7.1 Hz, CHCH3), 6.75–6.85 (m, 2H, Ar), 6.95–7.05 (m,
2H, Ar), 7.10–7.23 (m, 3H, Ar), 7.30–7.40 (m, 2H, Ar),
7.93 (br s, 1H, NH). 13C NMR: d¼22.7, 36.2, 55.3, 111.2,
113.8, 119.3, 119.8, 121.2, 121.8, 122.0, 127.0, 128.5, 136.8,
139.2, 157.8. IR (pellets): n¼3367, 2970, 2863, 1608, 1509,
1459, 1441, 1424, 1338, 1264, 1237, 1178, 1101,
1024 cmꢂ1. GC–MS (EI): tR¼13.4; m/z (%)¼251 (37)
[M+], 236 (100), 192 (27). ESHRMS: calcd for
C17H18NO: 252.1388. Found: 251.1383.
6. (a) Mertins, K.; Iovel, I.; Kischel, J.; Zapf, A.; Beller, M. Adv.
Synth. Catal. 2006, 348, 691–695; (b) Iovel, I.; Mertins, K.;
Kischel, J.; Zapf, A.; Beller, M. Angew. Chem., Int. Ed. 2005,
44, 3913–3917; (c) Mertins, K.; Iovel, I.; Kishel, J.; Zapf, A.;
Beller, M. Angew. Chem., Int. Ed. 2005, 44, 238–242.
7. (a) Anastas, P. T.; Warner, J. C. Green Chemistry, Theory and
Practice; Oxford University Press: Oxford, 1998; (b)
Lancaster, M. Green Chemistry, An Introductory Text; Royal
Society of Chemistry: Cambridge, 2002.
8. (a) Rosenfeld, D. C.; Shekhar, S.; Takemiya, A.; Utsunomiya,
M.; Hartwig, J. F. Org. Lett. 2006, 8, 4179–4182; (b) Li, Z.;
Zhang, J.; Brouwer, C.; Yang, C.-G.; Reich, N. W.; He, C.
Org. Lett. 2006, 8, 4175–4178; (c) Motokura, K.; Nakagiri,
N.; Mori, K.; Mizugaki, T.; Ebitani, K.; Jitsukawa, K.;
Kaneda, K. Org. Lett. 2006, 8, 4617–4620.
4.3.26. 2-(1-(4-Methoxyphenyl)ethyl)-1H-pyrrole (3ef).31
Pale yellow oil. 1H NMR: d¼1.49 (d, J¼7.2 Hz, 3H,
CHCH3), 3.68 (s, 3H, OCH3), 3.94 (q, J¼7.2 Hz, 1H,
CHCH3), 5.95–6.00 (m, 1H, CH-pyrrole), 6.03–6.09 (m,
1H, CH-pyrrole), 6.49–6.55 (m, 1H, CH-pyrrole), 6.70–
6.79 (m, 2H, Ar), 6.97–7.05 (m, 2H, Ar), 7.60 (br s, 1H, NH).
9. Zhang, L.; Sun, J.; Kozmin, S. A. Tetrahedron 2006, 62,
11371–11380.
10. Kotsuki, H.; Ohishi, T.; Inoue, M.; Kojima, T. Synthesis 1999,
602–606.
11. Wang, B.-Y.; Jiang, R.-.S.; Li, J.; Shi, M. Eur. J. Org. Chem.
2005, 4002–4008.
12. Fukuzawa, S.-i.; Tsuchimoto, T.; Hiyama, T. J. Org. Chem.
1997, 62, 151–156.
4.3.27. Preparation of (benzhydryloxy)diphenylmethane
(7d).32 A 50 mL round-bottomed flask was charged with
benzhydrol (184 mg, 1.0 mmol), CH2Cl2 (1 mL), and
CF3SO3H (4 mL, 0.05 mmol) at 0 ꢀC. The mixture was
heated (oil bath, 50 ꢀC) for 1 h. After cooling to room
temperature, saturated NaHCO3 (5 mL) was added and the
mixture was extracted with Et2O (5ꢁ5 mL). Organic phase
was dried over MgSO4, filtered, solvent was removed under
reduced pressure, and the product was purified by column
chromatography on silica gel (petroleum ether/ethyl acetate
98/2, then petroleum ether/ethyl acetate 95/5) to yield
13. Hashmi, A. S. K.; Schwarz, L.; Rubenbauer, P.; Blanco, M. C.
Adv. Synth. Catal. 2006, 348, 705–708.
14. Shirakawa, S.; Kobayashi, S. Org. Lett. 2006, 8, 4939–4942.
15. (a) Anderson, L. L.; Arnold, J.; Bergman, R. G. J. Am. Chem.
Soc. 2005, 127, 14542–14543; (b) Cherian, A. E.; Domski,
G. J.; Rose, J. M.; Lobkovsky, E. B.; Coates, G. W. Org. Lett.
2005, 7, 5135–5137.
1
7d (152 mg, 0.43 mmol, 87%). H NMR: d¼5.32 (s, 2H,
CH–O), 7.12–7.34 (m, 20H, Ar).
References and notes
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7948
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21. Sanz, R.; Martınez, A.; Miguel, D.; Alvarez-Gutierrez, J. M.;
ꢂ
Rodrıguez, F. Adv. Synth. Catal. 2006, 348, 1841–1845.
ꢂ
ꢂ
22. Caution: direct addition of triflic acid to 2-methylfuran
gives a violent reaction, see Section 4.3 for adapted
procedure.
28. Newcomb, M.; Varick, T. R.; Goh, S.-H. J. Am. Chem. Soc.
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23. (a) For 2-alkylated furans, see Refs. 1b and 6b; (b) For
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