Addition of heterocycles to electron deficient olefins and alkynes catalyzed by gold(III)

Article abstract of DOI:10.1016/j.jorganchem.2005.03.009

A gold(III)-catalyzed hydroarylation of different olefins is reported here. AuCl₃ works as an excellent catalyst to mediate reactions between various heterocycles and electron deficient olefins and alkynes under mild conditions. This gold(III)-based method tolerates different functional groups such as aldehyde, carboxylic acid, nitrile, and is highly efficient. We have shown that some of these reactions complete in minutes at room temperature.

Full text of DOI:10.1016/j.jorganchem.2005.03.009

Journal of Organometallic Chemistry 690 (2005) 5049–5054
www.elsevier.com/locate/jorganchem
Addition of heterocycles to electron deficient olefins
and alkynes catalyzed by gold(III)
*
Zigang Li, Zhangjie Shi, Chuan He
Department of Chemistry, The University of Chicago, 5735 S. Ellis Avenue, Chicago, IL 60637, United States
Received 6 February 2005; received in revised form 6 March 2005; accepted 7 March 2005
Available online 19 April 2005
Abstract
A gold(III)-catalyzed hydroarylation of different olefins is reported here. AuCl3 works as an excellent catalyst to mediate reac-
tions between various heterocycles and electron deficient olefins and alkynes under mild conditions. This gold(III)-based method
tolerates different functional groups such as aldehyde, carboxylic acid, nitrile, and is highly efficient. We have shown that some
of these reactions complete in minutes at room temperature.
Ó 2005 Elsevier B.V. All rights reserved.
Keywords: Hydroarylation; Gold; Heterocycle; Olefin; C–H Functionalization
1. Introduction
with methyl vinyl ketone to afford a new C–C bond.
After HashmiÕs work, Reetz and Sommer [6] and we re-
ported the direct addition of arenes to triple bonds with
slightly different catalyst systems. A combination of
AuCl3/3AgSbF6 or AuCl3/3AgOTf was shown to have
enhanced activity that works for many arene substrates.
We also developed the cyclialkylation of electron rich
arenes with tethered epoxides and the direct functional-
ization of arenes by primary alcohol sulfonate esters cat-
alyzed by gold(III) [7]. Our studies suggest that gold(III)
directly attacks the arenes and afford arylgold(III) spe-
cies as the reaction intermediates. The similar system
has also been used by Luo and Li [8] for addition of are-
nes to activated imines and addition of activated meth-
ylenes to olefins.
We report here the gold(III)-catalyzed addition of
various heterocycles to activated olefins and alkynes.
A variety of structures can be prepared with high
efficiency and under mild conditions. The reactions
described here can tolerate various functional
groups and are practical in constructing complex
molecules.
The direct addition of arenes to alkenes or alkynes to
form C–C bonds via C–H functionalization provides
efficient and atom-economic synthetic methods [1]. Such
reactions that work under mild conditions are particu-
larly desirable, and have attracted extensive research ef-
forts in the past [2].
Recently, gold-mediated organic transformations in
solution have emerged as important methodologies [3].
We and others have developed new methods to directly
functionalize aromatic C–H groups catalyzed by gold-
(III). It has been known for over seven decades that
gold(III) can attack arenes electrophilically to afford
arylgold(III) species [4]. This interesting property of
gold(III) has been studied but never really utilized in or-
ganic synthesis until 2000, when Hashmi et al. [5] re-
ported the gold(III)-catalyze coupling of 2-methylfuran
*
Corresponding author. Tel.: +1 7737025061; fax: +1 7737020805.
E-mail address: chuanhe@midway.uchicago.edu (C. He).
0022-328X/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2005.03.009

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Z. Li et al. / Journal of Organometallic Chemistry 690 (2005) 5049–5054
2. Results and discussion
2.1. Reactions between heterocycles and electron deficient
olefins
ð1Þ
Heterocycles, particularly those containing oxygen or
nitrogen atoms in the ring, are important building
blocks for natural products and pharmaceutical re-
agents. Thus, development of efficient methods to func-
tionalize heterocyles is critical for synthetic chemistry
[9]. Because of their electron rich nature, heterocycles
should react with gold(III) readily to afford arylgold(III)
species, as Hashimi et al. [5] has demonstrated with 2-
methylfuran and Arcadi et al. [10] has shown with indole
derivatives. We began to investigate reactions between
various heterocyles and substituted olefins. We found
that a variety of heterocycles can readily add to electron
deficient olefins at room temperature in acetonitrile or
dichloroethane (DCE) catalyzed by AuCl3 Eq. (1).
Good to excellent isolated yields can be obtained as
summarized in Table 1.
Indole and its derivatives afforded high yields of the
products (entries 1–4, Table 1). Notably, indole itself
can be used directly to react with methyl vinyl ketone
without any protecting group and 95% isolated yield
was obtained for this reaction (entry 1). Other heterocy-
cles, furan and benzofuran (entries 5, 6) also served as
good substrates under the same conditions. C–C bond
formations at the 3-position for indole and 2-position
for furan/benzofuran were observed, as expected. Furan
can undergo double addition to two equivalents of ole-
fins in very good yield (entry 6).
AuCl3 (5 mol%) serves as a good catalyst for the reac-
tions involving heterocycles. When 1,3,5-trimethoxyben-
zene was used, 3 equivalents of AgOTf is required as the
co-catalyst to afford good yields of the addition product.
The role of AgOTf is thought to help remove chloride
from AuCl3 and generate a more electrophilic cationic
gold(III) species. In the presence of AgOTf, 1,3,5-
trimethoxybenzene readily reacted with methyl vinyl
ketone or methyl acrylate to afford almost quantitative
yields of the final products at room temperature Eq.
(2). When 2-cyclohexen-1-one was used as the olefin
substrate, a slightly lower yield was obtained (80%), per-
haps due to the steric reason Eq. (3).
Table 1
Hydroarylation of activated olefins with heterocyclesa
ð2Þ
ð3Þ
2.2. Various electron deficient olefins can be used as the
substrates
We further explored the reaction with the use of dif-
ferent olefins. To our surprise, our catalytic system tol-
erates not only ketone and ester but also aldehyde,
carboxylic acid, and nitrile, as shown in Table 2.
The reactions of a,b-unsaturated aldehydes with
furans or a protected indole gave good yields of the
a
All reactions were carried out with 0.5 mmol of the heterocycle at
room temperature in CH3CN (heterocycle:olefin:AuCl3/1:1.5:0.05).
b
Isolated yield.
Heterocycle:olefin:AuCl3/1:2.5:0.05.
c

Z. Li et al. / Journal of Organometallic Chemistry 690 (2005) 5049–5054
5051
Table 2
Addition of heterocycles and electron-rich arenes to olefins with
different functional groups
yields of the products (52% and 41%, respectively) were
obtained from these reactions. The reactions between
arenes and acrylic acid or acrylonitrile were performed
at 80 °C to give the best yields. We want to point out
that most of the reactions described in Tables 1 and 2
can be run in the absence of solvents. Similar or better
yields were typically obtained under the solvent-free
conditions.
2.3. Reaction with ethyl propiolate
When ethyl propiolate was used to react with indole
and 2,3-benzofuran (1:1.2/arene:alkyne) in acetonitrile,
we were surprised to find that the only products we ob-
served and isolated were the double addition products,
as shown in Eqs. 4 and 5. Two equivalents of the hetero-
cycles were added to one molecule of ethyl propiolate in
this reaction. These results may indicate that the first
addition of the arene to ethyl propiolate gives an acti-
vated alkene, which reacts faster with the second equiv-
alent of arene to afford the final product. Similar double
addition result has been reported by Fujiwara and
coworkers [11] using acetic acid. However, when 1,3,5-
trimethoxybenzene was used, no double addition prod-
uct was obtained under the same condition. In addition,
ethyl propiolate did not react with indole in the presence
of 20 mol% of HCl without AuCl3 under the same con-
ditions. It appears that the a,b unsaturated ketone inter-
mediates with a heterocycle at the b position are quite
reactive and can react further with the heterocycle in this
system.
a
Reactions were carried out with 5% AuCl3 at room temperature in
acetonitrile (heterocycle:olefin:AuCl3/1:1.5:0.05).
b
Reactions were carried out with 5% AuCl3/3AgOTf at 80 °C in
DCE (heterocycle:olefin/1:1.5). The isolated yields are reported except
for entry 6.
c 1H NMR yield.
ð4Þ
addition products at room temperature (entries 1–4, Ta-
ble 2). Two equivalents of the olefin were attached to
furan to afford the di-substituted furan (entry 3), as also
observed in reactions described in Table 1. In entry 5,
acrylic acid was used to react with 1,3,5-trimethoxy-
benzene with 5 mol% of AuCl3/3AgOTf to afford a good
yield of the addition product. In fact, a reaction between
N-methylindole and acrylic acid was also tested. A prod-
ð5Þ
The reaction rate between indole and methyl vinyl ke-
1
uct yield of 64% was observed based on H NMR with
an internal standard. The product was not isolated due
to difficulties in its separation by column chromatogra-
phy (entry 6). These results show a significant advantage
of this method: substrates bearing aldehydes and acids
do not need to be protected. We further examined the
reactivity of acrylonitrile with N-methylindole and
1,3,5-trimethoxybenzene (entries 7 and 8). Reasonable
1
tone at room temperature was monitored by H NMR
in CDCl3. To a mixture of these two substrates in a
1
NMR tube was added 3% AuCl3/3AgOTf and the H
NMR spectrum was taken immediately after the addi-
tion. Only the product peak could be identified from
the spectrum. The reaction completed in less than 5

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Z. Li et al. / Journal of Organometallic Chemistry 690 (2005) 5049–5054
min at room temperature. Another arene substrate,
1,3,5-trimethoxybenzene, was examined with AuCl3/
3AgOTf in the same manner, and the similar result
(m, 2H), 7.01 (m, 1H), 6.8 (s, 1H), 5.06 (t, J = 7.0 Hz,
1H), 3.77 (tt, J = 7.0 Hz, 5.2 Hz, 2H), 3.71 (s, 3H);
13C NMR (CDCl3/TMS): d 198.2, 144.4, 137.3, 137.1,
133.0, 128.6, 128.4, 128.1, 127.8, 126.9, 126.2, 121.7,
119.6, 118.8, 117.8, 109.2, 45.3, 38.05, 32.7.
1
was detected by H NMR.
3. Summary
4.4. 4-(1-Allyl-1H-indol-3-yl)-butan-2-one (1d)
In this paper, we presented a highly efficient method to
functionalize heterocycles with electron deficient alkenes
and alkynes. Indole, furan and benzofuran all serve as
good substrates for the gold(III)-catalyzed hydroaryla-
tion of the activated alkenes/alkynes at ambient temper-
atures. Functional groups such as aldehyde, carboxylic
acid and nitrile can be tolerated. The reactions also pro-
ceed remarkably fast and complete in minutes at room
temperature. The method described here can be broadly
utilized to construct heterocycle-based structures.
1H NMR (CDCl3/TMS): d 7.57 (m, 1H), 7.27 (m,
1H), 7.20 (m, 1H), 7.10 (m, 1H), 6.86 (s, 1H), 5.95 (m,
1H), 5.16 (d, J = 11.4 Hz, 1H), 5.04 (d, J = 11.4 Hz,
1H), 4.63 (d, J = 4 Hz, 2H), 3.02 (t, J = 7.6 Hz, 2H),
2.81 (t, J = 7.6 Hz, 2H), 2.11 (s, 3H); 13C NMR: d
208.7, 136.3, 133.5, 127.7, 125.2, 121.5, 118.8, 118.7,
117.1, 114.0, 109.5, 48.5, 44.1, 30.0, 19.2.
4.5. 4-Benzofuran-2-yl-butan-2-one (1e)
1H NMR (CDCl3/TMS): d 7.46 (m, 1H), 7.40 (m,
1H), 7.21 (m, 2H), 6.39 (s, 1H), 3.06 (t, J = 7.1 Hz,
2H), 2.89 (t, J = 7.1 Hz, 2H), 2.18 (s, 3H); 13C NMR
(CDCl3/TMS): d 206.7, 157.6, 154.6, 128.7, 123.3,
122.5, 120.3, 110.6, 102.3, 41.2, 29.9, 22.5.
4. Experimental
All reagents were obtained commercially and used
without further purification unless otherwise noted. All
reactions were performed under air atmosphere in aceto-
nitrile or dichloroethane. Chromatographic purification
of products was accomplished using forced-flow chro-
matography on EM Science Geduran silica gel 60 (35–
75 lm). Thin layer chromatography was performed on
EM Science silica gel 60 F254 plates (250 lm). Proton
nuclear magnetic resonance (NMR) spectra were refer-
enced internally according to residual protio solvent sig-
nals. Data for 1H NMR are recorded as follows:
chemical shift (d, ppm), multiplicity (s, singlet; d, dou-
blet; t, triplet; m, multiplet), integration, coupling con-
stant (Hz). Data for 13C NMR are reported in terms
of chemical shift (d, ppm).
4.6. 4-[5-(3-Oxo-butyl)-furan-2-yl]-butan-2-one (1f)
1H NMR (CDCl3/TMS): d 5.86 (s, 2H), 2.85 (t,
J = 7.8 Hz, 4H), 2.77 (t, J = 7.8 Hz, 4H), 2.17 (s, 6H);
13C NMR (CDCl3/TMS): d 185.2, 152.3, 105.7, 41.7,
29.9, 22.2.
4.7. 4-(2,4,6-Trimethoxy-phenyl)-butan-2-one (1g)
1H NMR (CDCl3/TMS): d 6.11 (s, 2H), 3.79 (s, 6H),
3.77 (s, 3H), 2.83 (t, J = 7.5 Hz, 2H), 2.55 (t, J = 7.5 Hz,
2H), 2.14 (s, 3H); 13C NMR (CDCl3/TMS): d 209.7,
159.4, 158.6, 109.3, 90.3, 55.5, 55.2, 43.5, 29.5, 17.4;
MS m+ (%): 238.
4.1. 4-(1H-Indol-3-yl)-butan-2-one (1a)
1H NMR (CDCl3/TMS): d 8.11 (b, 1H), 7.55 (m, 1H),
7.25 (m, 1H), 7.15 (m, 1H), 7.07 (m, 1H), 6.86 (m, 1H),
3.03 (t, J = 7.6 Hz, 2H), 2.80 (t, J = 7.6 Hz, 2H), 2.09 (s,
3H); 13C NMR (CDCl3/TMS): d 209.1, 136.1, 127.0,
121.8, 121.5, 119.1, 118.5, 114.7, 111.1, 43.9, 29.9, 19.2.
4.8. 3-(2,4,6-Trimethoxy-phenyl)-propionic acid methyl
ester (1h)
1H NMR (CDCl3/TMS): d 6.11 (s, 2H), 3.80 (s, 3H),
3.78 (s, 6H), 3.67 (s, 3H), 2.90 (t, J = 7.9 Hz, 2H), 2.45
(t, J = 7.9 Hz, 2H), 13C NMR (CDCl3/TMS): d 174.2,
159.5, 158.6, 109.0, 90.2, 55.4, 55.1, 51.3, 33.6, 18.3;
MS m+ (%): 254.
4.2. 4-(1-Methyl-1H-indol-3-yl)-butan-2-one (1b)
1H NMR (CDCl3/TMS): d 7.57 (m, 1H), 7.27 (m,
2H), 7.11 (m, 1H), 6.81 (s, 1H), 3.72 (s, 3H), 3.05 (t,
J = 7.4 Hz, 2H), 2.82 (t, J = 7.4 Hz, 2H), 2.14 (s, 3H).
4.9. 3-(2,4,6-Trimethoxy-phenyl)-cyclohexanone (1i)
1H NMR (CDCl3/TMS): d 6.12 (s, 2H), 3.78 (s, 3H),
3.76 (s, 6H), 3.62 (m, 1H), 3.10 (t, J = 12.3 Hz, 1H), 2.36
(m, 2H), 2.26 (m, 2H), 2.03 (m, 1H), 1.70 (m, 2H); 13C
NMR (CDCl3/TMS): d 212.4, 159.4, 158.8, 112.2, 90.7,
55.3, 55.0, 45.3, 41.2, 33.8, 28.8, 25.4, MS m+ (%):
265.0 (M + 1+).
4.3. 3-(1-Methyl-1H-indol-3-yl)-1,3-diphenyl-propan-1-
one (1c)
1H NMR (CDCl3/TMS): d 7.93 (m, 2H), 7.53 (m,
1H), 7.44 (m, 3H), 7.36 (m, 2H), 7.25 (m, 3H), 7.13

Z. Li et al. / Journal of Organometallic Chemistry 690 (2005) 5049–5054
5053
4.10. 3-(1-Methyl-1H-indol-3-yl)-propionaldehyde (2a)
4.17. 3,3-Bis-benzofuran-3-yl-propionic acid ethyl ester
(2i)
1H NMR (CDCl3/TMS): d 9.79, (s, 1H), 7.54 (m,
1H), 7.26 (m, 2H), 7.07 (m, 1H), 6.81 (s, 1H), 3.69 (s,
3H), 3.07 (t, J = 7.2 Hz, 2H), 2.77 (t, J = 7.2 Hz, 2H);
13C NMR (CDCl3/TMS): d 202.6, 136.9, 127.3, 126.3,
121.6, 118.7, 118.6, 112.9, 109.2, 44.1, 32.5, 17.6.
1H NMR (CDCl3/TMS): d 7.61–7.42 (m, 2H), 7.43–
7.42 (m, 2H), 7.28–7.25 (m, 2H), 7.21–7.20 (m, 2H),
7.19 (s, 2H), 4.95 (t, J = 7.5 Hz, 1H), 4.14 (q, J = 7.0
Hz, 2H), 3.23 (d, J = 7.5 Hz, 2H) 1.19 (q, J = 7.0 Hz,
3H); 13C NMR (CDCl3/TMS): d 170.7, 155.9, 154.8,
128.3, 124.0, 122.8, 120.8, 111.1, 103.7, 60.9, 37.0,
36.1, 14.1.
4.11. 3-[5-(3-Oxo-propyl)-furan-2-yl]-propionaldehyde
(2c)
1H NMR (CDCl3/TMS): d 9.81 (s, 2H), 5.89 (s, 2H),
2.98 (t, J = 7.2 Hz, 4H), 2.79 (t, J = 7.2 Hz, 4H); 13C
NMR (CDCl3/TMS): d 201.2, 152.5, 106.0, 41.8, 20.7.
Acknowledgements
This research was supported by the University of
Chicago. We acknowledge the donors of the American
Chemical Society Petroleum Research Fund for support
of this research (PRF 38848-G3). This research is also
supported by a Research Innovation Award (RI1179)
from Research Corporation.
4.12. 3-(5-Methyl-furan-2-yl)-propionaldehyde (2d)
1H NMR (CDCl3/TMS): d 9.75 (s, 1H), 5.87 (d,
J = 19 Hz, 2H), 2.92 (t, J = 7.2 Hz, 2H), 2.75 (t,
J = 7.2 Hz, 2H), 2.22 (s, 3H).
4.13. 3-(2,4,6-Trimethoxy-phenyl)-propionic acid (2e)
References
1H NMR (CDCl3/TMS): d 6.12 (s, 2H), 3.80 (s, 3H),
3.79 (s, 6H), 2.92 (t, J = 6.5 Hz, 2H), 2.51 (t, J = 6.5 Hz,
2H); 13C NMR (CDCl3/TMS): d 180.4, 159.6, 158.7,
108.8, 90.3, 55.5, 55.2, 33.7, 18.1.
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