Homogeneous silver(I) salts and heterogeneous Ag3PW 12O40-catalyzed intermolecular allylation of arenes with allylic alcohols

Article abstract of DOI:10.1055/s-0031-1289548

AgOTf is an effective catalyst for intermolecular allylation of aromatic and heteroaromatic compounds with allylic alcohols affording allylated arenes in up to 99% yields. Heterogeneous allylation of arenes catalyzed by Ag ₃PW₁₂O₄₀ gave comparable product yields to those obtained by AgOTf. Ag₃PW₁₂O₄₀ could be reused five times with slightly decreased activity. Georg Thieme Verlag Stuttgart · New York.

Full text of DOI:10.1055/s-0031-1289548

LETTER
2713
Homogeneous Silver(I) Salts and Heterogeneous Ag3PW12O40-Catalyzed
Intermolecular Allylation of Arenes with Allylic Alcohols
Intermolecular
All
u
ylation of
A
r
o
enes with A
l
-
lylic
A
lc
Q
ohols iang Chen,a Zhen-Jiang Xu,a Sharon Lai-Fung Chan,b Cong-Ying Zhou,b Chi-Ming Che*a,b
a
Shanghai-Hong Kong Joint Laboratory in Chemical Synthesis, Shanghai Institute of Organic Chemistry,
345 Ling Ling Road, 200032 Shanghai, P. R. of China
b
Department of Chemistry, State Key Laboratory of Synthetic Chemistry, and Open Laboratory of Chemical Biology
of the Institute of Molecular Technology for Drug Discovery and Synthesis, The University of Hong Kong, Pokfulam Road,
Hong Kong, P. R. of China
Fax +86(852)28571586; E-mail: cmche@hku.hk
Received 31 July 2011
S1 in the supporting information. AgOTf displayed the
best performance affording the allylated product 3a in
40% yield. No reaction was observed when AuCl3 or
Au(SMe2)Cl was used as the catalyst. The Brønsted acid,
Abstract: AgOTf is an effective catalyst for intermolecular allyla-
tion of aromatic and heteroaromatic compounds with allylic alco-
hols affording allylated arenes in up to 99% yields. Heterogeneous
allylation of arenes catalyzed by Ag3PW12O40 gave comparable
product yields to those obtained by AgOTf. Ag3PW12O40 could be HOTf and Lewis acid BF3·Et2O, led to 3a in 15% and 10%
reused five times with slightly decreased activity.
yields, respectively (entries 11 and 18, Table S1). Using
AgOTf as catalyst, the reaction conditions were exam-
ined. The use of excessive 1a (20 mL, 162 mmol) and in-
creasing catalyst loading (15 mol% based on allylic
alcohol) improved the product yield to 83% and the reac-
tion was completed in two hours (entry 15, Table S2 in the
Supporting Information). Lowering temperature to 80 °C
led to a long reaction time (3 d) and a slightly lower prod-
uct yield of 79% (entry 6, Table S2).
Key words: allylation, allylic alcohols, silver catalysis, Friedel–
Crafts alkylation, recyclable
Friedel–Crafts allylation is a useful tool for the synthesis
of aromatic compounds.1 The most widely used allylation
reagents are allylic acetates, carbonates, and halides. With
the increasing demand of environmentally benign reac-
tions for chemical synthesis, Friedel–Crafts allylation
with allylic alcohol has been attracting considerable atten-
tion as water is the only by-product of this reaction. The
complexes of scandium,2 iron,3 molybdenum,4 rutheni-
um,5–7 palladium,8,9 indium,10 and gold,11 and Brønsted
acids12 have been demonstrated to be effective to catalyze
intermolecular Friedel–Crafts allylation of arenes2,5,6,11
and heteroaromatic compounds3,4,5b,7–11 (particularly
indoles3,7,8a,9,10) with allylic alcohols.
cat.
(5 mol%)
OH
+
140 °C
2a
3a
1a
Scheme 1 Friedel–Crafts allylation with cinnamyl alcohol
We have been interested in the use of silver(I) compounds
to mediate organic reactions owing to the inexpensive-
ness, stability towards air and moisture, and easy handling
and storage, of silver(I) compounds. In literature, a variety
of organic reactions mediated by silver compounds have
been demonstrated to have useful applications in organic
synthesis.13 Herein we report homogeneous and heteroge-
neous intermolecular Friedel–Crafts allylic alkylation of
arenes with allylic alcohols catalyzed by AgOTf and
Ag3PW12O40, respectively.
With the optimal conditions, the scope of allylic alcohols
for the AgOTf-catalyzed allylation of 1a was examined.
As depicted in Table 1, a variety of allylic alcohols were
found to react with 1a in the presence of AgOTf to afford
allylation products in good to high product yields. The re-
actions of (E)-cinnamyl alcohol derivatives bearing elec-
tron-withdrawing substituent(s) on the phenyl ring gave
high product yields (entries 2–7, Table 1), whereas the
relatively more electron-donating p-methyl substituent
rendered the reaction less efficient giving 40% yield of
At the outset, we examined intermolecular Friedel–Crafts allylation product (entry 8). Trisubstituted (E)-cinnamyl
allylic alkylation by using p-xylene (1a) and (E)-cinnamyl alcohol 2i reacted with 1a to give the allylated product 3i
alcohol (2a) at 140 °C (Scheme 1). A panel of metal cata- in 88% yield (entry 9). Terminal allylic alcohol 2j reacted
lysts were screened including Au(PR3)Cl–AgOTf, AuCl3, with 1a to give 3a in 89% yield (entry 10). Aliphatic allyl-
–
–
–
Au(SMe2)Cl, PtCl2, AgX (X = OTf–, SbF6 , BF4 , PF6 , ic alcohols were less reactive than cinnamyl alcohol giv-
–
ClO4 ), and Cu(OTf)2. The results are depicted in Table ing the products in moderate yields (entries 11 and 12).
The propargylic alcohol 2n gave the propargylated prod-
uct 3n in 27% yield (entry 13).
SYNLETT 2011, No. 18, pp 2713–2718
Advanced online publication: 19.10.2011
DOI: 10.1055/s-0031-1289548; Art ID: W17011ST
x
x
.x
x
.2
0
1
1
Next, the scope of arenes was examined by using (E)-cin-
namyl alcohol (2a) as allylation reagent. As depicted in
© Georg Thieme Verlag Stuttgart · New York

2714
G.-Q. Chen et al.
LETTER
Table 2, all of the monosubstituted, disubstituted and o/m = 20:80, o/o¢/m = 11:0:89, and o/m/p = 12:0:88, re-
trisubstituted arenes underwent Ag(I)-catalyzed allylation spectively was obtained (entries 1, 2 and 4, Table 2). Tol-
with 2a to give corresponding products in good to high uene was allylated in a lower yield (entry 5, Table 2). In
yields (entries 1–5, Table 2). When 1b, 1c, or 1e was contrast to electron-rich arenes, the reactions of benzene,
used, a mixture of regioisomers in each case with ratios of chlorobenzene and nitrobenzene were sluggish.
Table 1 Allylation of p-Xylene (1a) with Allylic Alcohols Catalyzed by AgOTf
Entrya
Alcohol
Product
Yield (%)b
OH
1
83
2a
3a
OH
2
3
4
5
6
7
8
71
82
92
82
88
84
40
F
F
2b
3b
OH
Br
Br
2c
3c
OH
F3C
F3C
2d
3d
OH
O2N
O2N
2e
3e
OH
Cl
Cl
2f
3f
Cl
Cl
OH
2g
2h
3g
3h
OH
Synlett 2011, No. 18, 2713–2718 © Thieme Stuttgart · New York

LETTER
Intermolecular Allylation of Arenes with Allylic Alcohols
2715
Table 1 Allylation of p-Xylene (1a) with Allylic Alcohols Catalyzed by AgOTf (continued)
Entrya
Alcohol
Product
Yield (%)b
OH
9
88
2i
3i
OH
10
89
53
60
2j
3j
3k
3l
11c
OH
2k
12c
OH
OH
2l
13
27
2n
3n
a Reaction conditions: arene (20 mL), (E)-cinnamyl alcohol (0.5 mmol), AgOTf (15 mol%), 140 °C, 2 h.
b Isolated yield.
c Reaction time was 5 h.
After achieving allylation of arenes with allylic alcohols, namyl ether (8) was observed to develop at the beginning
we extended this protocol to heteroaromatic compounds. of the reaction and was subsequently consumed at the end
Treatment of furan with 2a in toluene at 100 °C gave the of the reaction. Treatment of 8 with 1a in the presence of
allylation product 5a in 21% yield (entry 1, Table 3). Un- AgOTf (15 mol%) at 140 °C for two hours afforded 3a in
der the same conditions, 2-methylfuran (4b) gave a better 80% yield. With these findings, we propose that allylation
result than furan affording a mixture of two regioisomers
AgOTf
5b and 7b with a ratio of 82:18 in overall 79% yield (entry
2). When thiophene (4c) was used, regioisomers 5c and 6c
were obtained in 94% yield with a ratio of 77:23. No iso-
mer 7c was observed (entry 3). In contrast, three regioiso-
1a
mers were obtained in a ratio of 5d/6d/7d = 79:2:19 when
2-methylthiophene (4d) was used (entry 4). Pyrrole (4e)
OH
was also reactive to undergo allylation giving 5e as the
2a
3a
major product (entry 5).
AgOTf
AgOTf
This AgOTf-catalyzed intermolecular allylation protocol
can be scaled up. Treatment of 1a (150 mL) with 2a (1.34
g) in the presence of AgOTf (15 mol%) at 140 °C for four
hours gave 3a (1.66 g) in 75% yield.
O
8
1a
To gain insight into the reaction mechanism, we moni-
tored the AgOTf-catalyzed allylation of 1a with 2a by 1H
NMR spectroscopy (see SI for the time course). Dicin-
Scheme 2 Proposed pathways in AgOTf-catalyzed allylation of 1a
with 2a
Synlett 2011, No. 18, 2713–2718 © Thieme Stuttgart · New York

2716
G.-Q. Chen et al.
LETTER
Table 2 Allylation of Arenes with (E)-Cinnamyl Alcohol (2a) Cat-
alyzed by AgOTf
Table 3 Allylation of Heteroaromatic Compounds with (E)-Cin-
namyl Alcohol (2a) Catalyzed by AgOTf
X
Entrya Arene
Product
Yield (%)b
X
R
R
5
o
4
80
AgOTf
m
1
(20:80)c
+
X
m
o
6
1b
OH
3o
3p
3q
R
2a
o
X
96
R
m
2
(11:0:89)d
7
m
o
Entrya
1
Substrate
Yield (%)b
21
5/6/7
1c
O
5a/6a/7a = 100:0:0
5b/6b/7b = 82:0:18
5c/6c/7c = 77:23:0
5d/6d/7d = 79:2:19
3
97
4a
O
1d
OMe
2
3
4
79
94
96
o
p
99
OMe
4
m
4b
S
o
(12:0:88)e
m
1e
3r
3s
4c
o
p
S
5f
70g
m
o
m
1f
4d
H
N
a Reaction conditions: arene (20 mL), (E)-cinnamyl alcohol (0.5
mmol), AgOTf (15 mol%), 140 °C, 2 h.
b Isolated yield.
5
92
5e/6e/7e = 70:15:15
4e
c Reaction time was 5 h.
d Isomer ratio o/o¢/m.
a Reaction conditions: heteroarene (0.05 mol), (E)-cinnamyl alcohol
(0.5 mmol), toluene (5 mL), AgOTf (15 mol%), 100 °C, 2 h.
b Isolated yield.
e Isomer ratio o/m/p.
f The reaction was carried out at 110 °C for 10 h.
g Isomer ratio could not be determined by 1H NMR.
Catalyst reusability in metal-catalyzed allylation of aro-
matic and heteroaromatic compounds with allylic alco-
hols has not been addressed in previous examples,2–11,14
except for the reaction catalyzed by Sc(OTf)3, in which
case Sc(OTf)3 was reused after evaporating the aqueous
mixture followed by subsequent heating in vacuo at 180
°C.2b
products were formed directly from allylic alcohols and
via intermediate 8 (Scheme 2). A similar mechanism was
previously reported in a diruthenium complex catalyzed
allylation.5b
a
Table 4 Allylation of Arenes with Allylic Alcohols Catalyzed by Ag3PW12O40
Entrya
Allylic alcohol
Product
Yield (%)b
OH
1
84
2a
3a
OH
2
70
F
F
2b
3b
Synlett 2011, No. 18, 2713–2718 © Thieme Stuttgart · New York

LETTER
Intermolecular Allylation of Arenes with Allylic Alcohols
2717
a
Table 4 Allylation of Arenes with Allylic Alcohols Catalyzed by Ag3PW12O40 (continued)
Entrya
Allylic alcohol
Product
Yield (%)b
OH
3
92
82
88
84
57
89
Br
Br
2c
3c
OH
4
5
6
7
8
F3C
F3C
2d
3d
OH
Cl
Cl
2f
3f
Cl
Cl
OH
2g
3g
3k
3a
OH
2k
OH
2j
OH
OH
9c
97
2a
2a
3q
5c
S
10d
96e
a Reaction conditions: p-xylene (20 mL), allylic alcohol (0.5 mmol), Ag3PW12O40 (15 mol%), 140 °C, 2 h.
b Isolated yield.
c Reaction was performed with.1,3,5-trimethylbenzene (20 mL).
d Thiophene (0.05 mol) in toluene (5 mL), 100 °C, 2 h.
e A regioisomeric ratio of 5:6:7 = 87:11:2 was determined by 1H NMR.
To address this issue, we synthesized a heterogeneous sil- allylation giving comparable product yields as those ob-
ver(I) catalyst Ag3PW12O40 according to the literature.15 tained in the homogenous Ag(I) catalysis (Table 4).
This silver(I) compound was characterized by PXRD,
Importantly, Ag3PW12O40 could be easily recovered and
SEM, and EDAX (see the Supporting Information). Then
reused by simple filtration of the reaction mixture after the
we used this compound to catalyze the intermolecular al-
reaction. As depicted in Table 5, after five recycles, the
lylation reaction. To our delight, this heterogeneous silver
catalyst Ag3PW12O40 was still active (Table 5).
compound Ag3PW12O40 showed high activity towards the
Synlett 2011, No. 18, 2713–2718 © Thieme Stuttgart · New York

2718
G.-Q. Chen et al.
LETTER
Table 5 Reuse of Ag3PW12O40 in Allylation of 1a with 2a
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Runa
1
2
3
4
5
Yield (%)b
84
81
77
71
62
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Ag3PW12O40 (15 mol%), 140 °C, 2 h.
b Isolated yield.
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In conclusion, we have demonstrated that AgOTf is an ef-
ficient catalyst for the intermolecular allylation of aromat-
ic and heteroaromatic compounds with allylic alcohols.
This method can be applied to a gram-scale synthesis. We
have also found that Ag3PW12O40 is an active and recycla-
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Acknowledgment
We are thankful for the financial support of The University of Hong
Kong (University Development Fund), Hong Kong Research Grant
Council (HKU 7052/07P), Research Grants Council (CityU 2/06C
and HKU1/CRF/08), CAS-GJHZ200816 and CAS-Croucher Fun-
ding Scheme for Joint Laboratory and the Areas of Excellence
Scheme established under the University Grants Committee of the
Hong Kong SAR, China (AoE/P- 10/01). G.-Q. Chen thanks the
Croucher Foundation of Hong Kong for the postgraduate stu-
dentship.
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