Organic hydrogen phosphites and hydrogen phosphates catalyzed Friedel-Crafts amidoalkylation of indoles with aryl aldimines

Article abstract of DOI:10.1016/j.tetlet.2011.07.010

A highly efficient and selective Friedel-Crafts amidoalkylation reaction of indoles with N-Ts aryl aldimines has been developed utilizing dimethyl hydrogen phosphite or diphenyl hydrogen phosphate as the organocatalysts, providing a facile and cost-effect

Full text of DOI:10.1016/j.tetlet.2011.07.010

Tetrahedron Letters 52 (2011) 4671–4674
Contents lists available at ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Organic hydrogen phosphites and hydrogen phosphates catalyzed
Friedel–Crafts amidoalkylation of indoles with aryl aldimines
⇑
⇑
Bei-Lei Wang, Jin-Xin Zhang, Nai-Kai Li, Guo-Gui Liu, Qi Shen , Xing-Wang Wang
Key Laboratory of Organic Synthesis of Jiangsu Province, College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou 215123, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
A highly efficient and selective Friedel–Crafts amidoalkylation reaction of indoles with N-Ts aryl aldi-
mines has been developed utilizing dimethyl hydrogen phosphite or diphenyl hydrogen phosphate as
the organocatalysts, providing a facile and cost-effective process for synthesis of 3-indolyl methanamine
derivatives in good to excellent yields. This transformation displays a broad substrate scope and wide
functional-group tolerability, regardless of the electronic and steric properties of N-Ts aryl aldimines.
Given that the developed catalytic Friedel–Crafts amidoalkylation reaction exhibits several salient fea-
tures such as metal-free catalysis, high efficiency, low cost and mild reaction condition, this process
might have practical applications in the synthesis of 3-indolyl methanamine derivatives.
Ó 2011 Elsevier Ltd. All rights reserved.
Received 12 May 2011
Revised 22 June 2011
Accepted 1 July 2011
Available online 8 July 2011
Keywords:
Hydrogen phosphites
Hydrogen phosphates
Indoles
Friedel–Crafts
Amidoalkylation
1. Introduction
Just in recent years, the Friedel–Crafts amidoalkylation of in-
doles with different imines have been successfully developed,
The 3-substituted indole structural motifs are widely presented
in pharmaceuticals, agrochemicals, indole alkaloids and synthetic
indole derivatives. In the past 10 years, synthesis of 3-indolyl deriv-
atives has attracted lot of interest and particularly synthesis of bio-
logically active 3-indolyl methanamines.1 Correspondingly, the
Friedel–Crafts alkylation2 of indoles with imines has turned out to
be an atom economic and short-armed method for the preparation
of 3-indolyl methanamine derivatives via addition of sp2
C–H bonds of indoles to C@N double bond of imines. Literatures
have been reported that various lewis acids, such as TiCl4,3 Sc(OTf),4
Dy(OTf)3,5 InCl3,6 SmI3,7 AuCl3/AgOTf,8 BF3ÁOEt2,9 are employed to
catalyze the Friedel–Crafts amidoalkylation of indole with imines.
However, due to the intrinsic instability of the benzylic amine
derivatives under the acidic reaction conditions, most of the reac-
tions catalyzed by lewis acids mentioned above furnish 3-indolyl
methanamine derivatives, and simultaneously generate the bis-
and tris(indolyl)methanes (BIMs and TIMs)5,10 in considerable
amounts (Scheme 1). Meanwhile, some strategies, such as utilizing
of ionic liquids,10 aqueous phase,11 ultrasound12 and Microwave,13
as well as mild reagents such as montmorillonite clay K-10/KSF14
and exchange resins,15 have been adopted and employed for the
corresponding Friedel–Crafts alkylation reactions, which provide
3-indolyl methanamines and also accompany with the BIMs and
TIMs as by-products or main products in some cases.
including asymmetric and non-asymmetric versions catalyzed by
metal and/or metal-free catalysts, thus allowing facile access to
3-indolyl methanamine derivatives in good yields or with high
enantioselectivities.16 Especially, some soft brønsted acids turn
out to be effective catalysts for the Friedel–Crafts amidoalkylation
of indoles with imines. You, Terada, and Antilla groups, respec-
tively, have demonstrated that chiral binaphthyl derived phospho-
ric acids can catalyze the asymmetric Friedel–Crafts alkylation of
indoles with imines, affording the corresponding 3-indolyl
methanamine derivatives in high yields with excellent enantiose-
lectivities.16e–g Kobayashi and Shirakawa have disclosed that the
linear alkyl carboxylic acids are effective catalysts for three-com-
ponent aza-Friedel–Crafts reactions in water, providing 3-indolyl
TsHN
Ar
Ar
Lewis acid
- TsNH2
HN
NH
N
H
"Hard"
Lewis acid
N
H
+
TsHN
"Soft"
Brønsted acid
Ar
Ts
N
Nonprotonic
solvent
High yields?
Ar
N
H
⇑
Corresponding authors. Tel./fax: +86 512 65880378.
E-mail address: wangxw@suda.edu.cn (X.-W. Wang).
Scheme 1. Friedel–Crafts amidoalkylation of indoles with N-Ts aryl aldimines
catalyzed by Lewis acid and brønsted acids.
0040-4039/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2011.07.010

4672
B.-L. Wang et al. / Tetrahedron Letters 52 (2011) 4671–4674
Table 1
product in a slightly higher yield (68%). When increasing the
Examination of catalystsb
amount of indole 2a to 3 equiv, an optimal result was obtained
in terms of 86% yield with bisindole 5 in less than 5% yield. Subse-
quently, 5 equiv of indoles were introduced and the yield was not
obviously affected (87%). Then diethyl hydrogen phosphite 1b and
diisopropyl hydrogen phosphite 1c were examined for this reac-
tion, affording the desired products in 42% and 34% yields and
the by-products of bis(indolyl)methanes in 12% and 10% yields,
respectively (entries 2–3). In comparison with 1b and 1c, diphenyl
hydrogen phosphite 1d was amenable to generate the desired
product in 65% yield and by-products in 8% yield (entry 4). Unex-
pectedly, diphenylphosphine oxide 1e was found to be ineffective
for the reaction, where essentially no product was obtained after
prolonged the reaction time (entry 5). To our delight, diphenyl
hydrogen phosphate 1f could smoothly catalyze this reaction to
provide the desired product in 78% yield, when 3 equiv amounts
of 2a were utilized. For this case, increasing the amount of 2a rel-
ative to that of 3a was found to slightly improve the yield of 4a.
When 5 equiv of 2a were used, the desired product was obtained
in 83% yields, which was accompanied with less than 5% yield of
the by-products (entry 6). Phenyl phosphinic acid 1g, which was
confirmed as effective catalyst for the acylcyanation of aldimines
and acylcyanides by List and Pan,18 was incompetent for the reac-
tion to provide the desired product 4a in 36% yield with 60% yield
of undesired by-products 5 being formed (entry 7). In addition,
phenylphosphonic acid 1h was also inefficient for this transforma-
tion, providing the desired product only in 27% yield and the unde-
sired by-products 5 in 69% yield (entry 8). Moreover, having
established by You’s group,16e the binaphthyl scaffold phosphoric
acid 1i was the really effective catalyst for this reaction, giving
the desired product in 80% yield (entry 9, Table 1). Thus, having
critically examined the mentioned catalysts, we found that the di-
methyl hydrogen phosphite 1a and diphenyl hydrogen phosphate
1f were effective catalysts. Finally, it should be worth noting that
the reactions catalyzed by 1a and 1f have proceeded very fast.
The reaction mixture generally becomes cloudy and thick within
10 min (picture (i) and (ii) for entry 1 in Table 1).
TsHN
Ph
Ph
Ts
N
cat. (20 mol%)
toluene
+
+
N
H
Ph
N
H
N
H
N
H
2a
3a
4a
5
(i)a
(ii)a
Entry
1
Catalyst
4a Yieldc (%)
5 Yieldc (%)
O
P H
OMe
O
MeO
EtO
1a
1b
1c
1d
1e
1f
86
<5
P
H
2
42
34
65
—
12
10
8
OEt
O
Pri O
PhO
P
H
3
O iPr
O
P
H
4
OPh
O
P H
Ph
Ph
5
—
O
6d
7
83
36
<5
60
PhO
Ph
P
OH
OPh
O
P
H
O
OH
OH
1g
Ph
P
8
1h
1i
27
80
69
<5
Further results on the optimization of the other parameters for
the reaction of indole 2a and aldimine 3a catalyzed by dimethyl
hydrogen phosphite 1a and diphenyl hydrogen phosphate 1f,
including solvent and catalyst loading, are summarized in Table
2. After screening several common solvents for the reaction, the
results indicated that toluene was the optimal solvent for the reac-
tion, affording the desired product in the highest yield (entries 1–
7). Furthermore, when the catalyst loading was decreased to
15 mol %, the yield was not influenced too much. When the cata-
OH
9d
(R)-BINOL phosphoric acid
a
The photographs: (i) before reaction and (ii) after reaction for entry 1.
Reaction conditions: catalysts 1a–i (20 mol %), 2a (1.5 mmol), 3a (0.5 mmol) in
b
toluene (3.0 mL) at rt for 2 h.
c
Isolated yield.
d
Reaction conditions: catalyst 1f (20 mol %), 2a (2.5 mmol), 3a (0.5 mmol), tol-
uene (3.0 mL) at rt for 2 h.
methanamines in high yields.17 Herein, we would like to present
our preliminary results on the Friedel–Crafts amidoalkylation of in-
doles with N-Ts aryl aldimines catalyzed by organic hydrogen
phosphites or hydrogen phosphates, providing the 3-indolyl meth-
anamines in high yields.
Table 2
Optimization of reaction conditionsa
Entry
Catalyst (mol %)
Solvent
Yieldb (%)
1
2
3
4
5
6
7
8
1a (20)
1a (20)
1a (20)
1a (20)
1a (20)
1a (20)
1a (20)
1a (15)
1a (10)
1a (5)
Toluene
Xylene
Benzene
CHCl3
DCM
ClCH2CH2Cl
THF
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
86
70
65
54
76
69
<5
90
51
46
81
85
75
2. Results and discussion
Initially, several common hydrogen phosphites or hydrogen
phosphates 1a–i were examined for the catalysis of the Friedel–
Crafts amidoalkylation of indole 2a and N-Ts aldimine 3a with
20 mol % of the catalyst loading in toluene at room temperature.
The results are summarized in Table 1. We found that dimethyl
hydrogen phosphite 1a was quite effective catalyst for the reaction
of 3a with one equivalent amount of 2a, affording the desired prod-
uct 4a in 50% yield within 2 h, albeit with bisindole 5 in 13% yield
as by-products. When two equivalent amounts of indole 2a were
used, the reaction did not proceed faster but led to the desired
9
10
11c
12c
13c
1f (15)
1f (10)
1f (5)
a
b
c
Reaction conditions: 2a (1.5 mmol), 3a (0.5 mmol), solvent (3.0 mL) at rt for 2 h.
Isolated yields.
Reaction conditions: 2a (2.5 mmol), 3a (0.5 mmol), toluene (3.0 mL) at rt for
2 h.

B.-L. Wang et al. / Tetrahedron Letters 52 (2011) 4671–4674
4673
Table 3
Table 4
Dimethyl hydrogen phosphite 1a catalyzed the Friedel–Crafts amidoalkylation of
Diphenyl hydrogen phosphate 1f catalyzed the Friedel–Crafts amidoalkylation of
indoles with N-Ts aryl aldiminesa
indoles with N-Ts aryl aldiminesa
O
O
TsHN
TsHN
MeO
P
H
PhO P OH
(1f)
OPh
(10 mol%)
Ar
Ar
(1a)
Ts
Ts
OMe
(15mol%)
toluene
N
N
R
R
+
R
+
R
toluene
N
H
N
H
Ar
N
H
N
H
Ar
2a-d
3a-q
4a-w
4a-t
2a-d
3a-q
Yieldb (%)
Entry
Indole (R)
Aldimine (Ar)
Product
Yieldb (%)
Entry
Indole (R)
Aldimine (Ar)
Product
1
2
3
4
5
6
7
8
H (2a)
H (2a)
H (2a)
H (2a)
H (2a)
H (2a)
H (2a)
H (2a)
H (2a)
H (2a)
H (2a)
H (2a)
H (2a)
H (2a)
H (2a)
H (2a)
Ph (3a)
4a
4b
4c
4d
4e
4f
4g
4h
4i
4j
4k
4l
4m
4n
4o
4p
4q
4r
85
80
78
79
75
81
80
80
81
89
81
79
78
81
75
87
86
87
89
86
95
90
92
1
2
3
4
5
6
7
8
H (2a)
H (2a)
H (2a)
H (2a)
H (2a)
H (2a)
H (2a)
H (2a)
H (2a)
H (2a)
H (2a)
H (2a)
H (2a)
H (2a)
H (2a)
H (2a)
H (2a)
5-Me (2b)
5-Br (2c)
7-Me (2d)
Ph (3a)
4a
4b
4c
4d
4e
4f
4g
4h
4i
90
89
91
82
80
88
83
91
88
88
81
84
85
89
60
84
81
57
59
54
p-FC6H4 (3b)
p-ClC6H4 (3c)
p-BrC6H4 (3d)
p-MeOC6H4 (3e)
p-CF3C6H4 (3f)
p-MeC6H4 (3g)
o-FC6H4 (3h)
o-ClC6H4 (3i)
o-BrC6H4 (3j)
o-MeOC6H4 (3k)
2,4-Cl2C6H3 (3l)
m-MeC6H4 (3m)
m-ClC6H4 (3n)
Thiophen-2-yl (3o)
1-Naphthyl (3p)
2-Naphthyl (3q)
Ph (3a)
p-FC6H4 (3b)
p-ClC6H4 (3c)
p-BrC6H4 (3d)
p-MeOC6H4 (3e)
p-CF3C6H4 (3f)
p-MeC6H4 (3g)
o-FC6H4 (3h)
o-ClC6H4 (3i)
o-BrC6H4 (3j)
o-MeOC6H4 (3k)
2,4-Cl2C6H3 (3l)
m-MeC6H4 (3m)
m-ClC6H4 (3n)
thiophen-2-yl (3o)
1-Naphthyl (3p)
2-Naphthyl (3q)
Ph (3a)
Ph (3a)
Ph (3a)
9
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
10
11
12
13
14
15
16
17
18
19
20
4j
4k
4l
4m
4n
4o
4p
4q
4r
4s
4t
H (2a)
5-Me (2b)
5-Br (2c)
7-Me (2d)
5-Me (2b)
5-Br (2c)
7-Me (2d)
Ph (3a)
Ph (3a)
o-ClC6H4 (3i)
o-ClC6H4 (3i)
o-ClC6H4 (3i)
4s
4t
4u
4v
4w
a
Reaction conditions: 2a-d (1.5 mmol), 3a–q (0.5 mmol) in toluene (3.0 mL) at rt
for 2 h.
b
Isolated yield.
a
Reaction conditions: 2a–d (2.5 mmol), 3a–q (0.5 mmol) in toluene (3.0 mL) at rt
for 2 h.
b
Isolated yield.
lyst loading was continued to decrease to 10 mol % and 5 mol %,
the yields rapidly dropped to 51% and 46%, respectively (entries
8–10). On the other hand, the catalyst loading was also investi-
gated for the Friedel–Crafts amidoalkylation of indole 2a with N-
Ts aldimine 3a catalyzed by diphenyl hydrogen phosphate 1f,
and 10 mol % of catalyst loading was found to be suitable for the
transformation, affording the desired product in 85% yield (entries
11–13).
Having established the optimal reaction conditions, we pro-
ceeded to explore the substrate scope and limitation utilizing di-
methyl hydrogen phosphite 1a as the catalyst. As shown in Table
3, the results indicated that all the reactions between N-Ts aryl
aldimines 3a–q and indole derivatives 2a–d were performed
smoothly in the presence of 15 mol % dimethyl hydrogen phos-
phite 1a. The N-Ts aryl aldimines 3a–n bearing ether electron-
donating substituents (–Me, –OMe) or electron-withdrawing sub-
stituents (–F, –Cl, –Br, –CF3) at para-, ortho- or meta-position on
phenyl group were all well tolerated, and the electronic and steric
properties of N-Ts aryl aldimines displayed little effect on their
reactivities, leading to their desired products in 80–91% yields (en-
tries 1–14). Moreover, the substrate 3o bearing 2-thienyl group
was also a suitable substrate for this reaction, furnishing the prod-
uct 4o in 60% yield (entry 15), Furthermore, aldimines 3p and 3q
The substrate scope and Limitation were also investigated for
the Friedel–Crafts amidoalkylation of N-Ts indole derivatives 2a–
d with aryl aldimines 3a–q catalyzed by diphenyl hydrogen phos-
phate 1f. The results are summarized in Table 4, the reactions pro-
ceeded more successfully in the presence of 10 mol % of diphenyl
hydrogen phosphate 1f at rt in toluene for 2 h. The substrates
3a–n with different electronic and steric properties all led to their
desired products 4a–n in good yields (75–89%) (entries 1–14). N-Ts
aryl aldimines 3o–q containing ether naphthyl groups or heteroar-
omatic ring were all suitable substrates for this transformation,
affording the corresponding products 4o–q in 75–87% yields (en-
tries 15–17). Pleasingly, the Friedel–Crafts amidoalkylation of in-
dole derivatives 2b–d with N-Ts aryl aldimine 3a and 3i,
respectively, performed very well to afford the desired products
4r–w in good to excellent yields (86–95%) (entries 18–23). It
should be noted that all the reactions have to be timely quenched
once the starting materials disappear, because the amount of bisin-
dole by-products would be enhanced with the prolonged reaction
time.
In summary, we have disclosed that dimethyl hydrogen phos-
phite or diphenyl hydrogen phosphate can efficiently catalyze the
Friedel–Crafts amidoalkylation of indoles with N-Ts aryl aldimines,
selectively affording 3-indolyl methanamines in good to excellent
yields. Furthermore, this transformation displays a broad substrate
scope and wide functional-group tolerability, regardless of the
electronic and steric properties of N-Ts aryl aldimines. The di-
methyl hydrogen phosphite (C2H7O3P) as the organocatalyst con-
tains two carbons, and the molecular weight is only 110.05,
which might be regarded as an atom economic and low carbonic
catalyst. More importantly, the present protocol displays several
salient features such as metal-free catalysis, high efficiency, low
cost and mild reaction condition, which might have practical appli-
bearing a-naphthyl, b-naphthyl groups also gave the desired prod-
ucts 4p and 4q in 84% and 81% yields, respectively (entries 16–17).
Among them, the reactions for substrates 3e, 3g, 3o and 3q oc-
curred relatively slow, as the time for turning translucent was
obviously prolonged for those reactions. Unfortunately, the present
protocol suffered from limitation in indole derivatives 2b–d as sub-
strates. Under the optimal conditions, the Friedel–Crafts amidoal-
kylation of indole derivatives 2b–d with 3a proceeded sluggishly
to afford the desired adducts 4r–t in moderate yields (54–59%)
within 2 h (entries 18–20). Further extending the reaction time,
the yields of bis(indolyl)methanes (BIMs) were visibly increased.

4674
B.-L. Wang et al. / Tetrahedron Letters 52 (2011) 4671–4674
M.; Melloni, A.; Umani-Ronchi, A. Angew. Chem. 2004, 116, 560–566; Angew.
Chem., Int. Ed. 2004, 43, 550–556; (g) Bandini, M.; Eichholzer, A. Angew. Chem.
2009, 121, 9697–9701; Angew. Chem., Int. Ed. 2009, 48, 9608–9644; (h) Zeng,
M.; You, S.-L. Synlett 2010, 1289–1301.
cations in the synthesis of 3-indolyl methanamine derivatives. Fur-
ther application of orthophosphorous acids or phosphoric acids as
the catalysts and extension of the reaction scope are currently
underway in our laboratory.
2. Selected examples of asymmetric Friedel–Crafts reactions, see: (a) Saaby, S.;
Fang, X.; Gathergood, N.; Jørgensen, K. A. Angew. Chem. 2000, 112, 4280–4282.
Angew. Chem., Int. Ed., 2000, 39, 4114–4116; (b) Austin, J. F.; MacMillan, D. W. C.
J. Am. Chem. Soc. 2002, 124, 1172–1173; (c) Evans, D. A.; Scheidt, K. A.; Fandrick,
K. R.; Lam, H. W.; Wu, J. J. Am. Chem. Soc. 2003, 125, 10780–10781; (d) Yuan, Y.;
Wang, X.; Li, X.; Ding, K. J. Org. Chem. 2004, 69, 146–149; (e) Zhou, J.; Tang, Y.
Chem. Commun. 2004, 432–433; (f) Uraguchi, D.; Sorimachi, K.; Terada, M. J. Am.
Chem. Soc. 2004, 126, 11804–11805; (g) Mori, K.; Katoh, T.; Suzuki, T.; Noji, T.;
Yamanaka, M.; Akiyama, T. Angew. Chem. 2009, 121, 9832–9834. Angew. Chem.,
Int. Ed., 2009, 48, 9652–9654; Cai, Q.; Zhao, Z.; You, S.-L. Angew. Chem., Int. Ed.
2009, 121, 7564–7567. Angew. Chem., Int. Ed., 2009, 48, 7428–7431; (i)
Nakamura, S.; Sakurai, Y.; Nakashima, H.; Shibata, N.; Toru, T. Synlett 2009,
1639–1642; (j) Wang, W.; Liu, X.; Cao, W.; Wang, J.; Lin, L.; Feng, X. Chem. Eur. J.
2010, 16, 1664–1669; (k) Tsubogo, T.; Kano, Y.; Yamashita, Y.; Kobayashi, S.
Chem. Asian J. 2010, 5, 1974–1977; (l) Jin, S.; Li, C.; Ma, Y.; Kan, Y.; Zhang, Y.;
Zhang, W. Org. Biomol. Chem. 2010, 8, 4011–4025; (m) Sakamoto, T.; Itoh, J.;
Mori, K.; Akiyama, T. Org. Biomol. Chem. 2010, 8, 5448–5454; (n) Wang, J.; Zhou,
P.; Wang, Y. Eur. J. Org. Chem. 2011, 264–270; (o) Wang, B.-L.; Li, N.-K.; Zhang,
J.-X.; Liu, G.-G.; Liu, T.; Shen, Q.; Wang, X.-W. Org. Biomol. Chem. 2011, 9, 2614–
2617.
2.1. General procedure for the catalytic Friedel–Crafts
amidoalkylation
N-Sulfonyl aldimines 3 (0.5 mmol) and dimethyl hydrogen phos-
phite 1a (0.075 mmol, 7.0 lL) or diphenyl hydrogen phosphate 1f
(0.05 mmol, 12.8 mg) were dissolved in toluene (3.0 mL). The solu-
tion was stirred at room temperature for 10 minutes. Subsequently,
2 (1.5 or 2.5 mmol) was added in one portion. After the reaction was
complete (monitored by TLC), 10% NaHCO3 (6 mL) was added to
quench the reaction. The mixture was extracted with ethyl acetate
(3 Â 5 mL). The combined organic phase was washed by H2O
(5 mL) and brine (5 mL) and dried over anhydrous Na2SO4. After fil-
tration, the solvent was removed under reduced pressure and the
residue was purified by flash chromatography (DCM/petroleum
ether = 1/3 to 1/0) to afford the product, which was determined by
ESI-MS, 1H and 13C NMR spectroscopy.
3. Chen, Y.-J.; Ge, C. S.; Wang, D. Synlett 2000, 1429–1432.
4. Huang, T.; Li, C.-J. Tetrahedron Lett. 2000, 41, 6715–6719.
5. Xie, W.; Bloomfield, K. M.; Jin, Y.; Dolney, N. Y.; Wang, P. G. Synlett 1999, 498–
500.
6. Babu, G.; Sridhar, N.; Perumal, P. T. Synth. Commun. 2000, 30, 1609–
1614.
7. Mao, H.; Wang, X.; Wang, W. Synthesis 2008, 16, 2582–2588.
8. Luo, Y. M.; Li, C.-J. Chem. Commun. 2004, 1930–1931.
Acknowledgments
We are grateful for the financial support from the National Nat-
ural Science Foundation of China (21072145), Foundation for the
Author of National Excellent Doctoral Dissertation of PR China
(200931), and Natural Science Foundation of Jiangsu Province of
China (BK2009115).
9. Gong, Y. F.; Kato, K.; Kimoto, H. Synlett 2000, 1058–1060.
10. Mi, X.; Luo, S.; He, J.; Cheng, J.-P. Tetrahedron Lett. 2004, 45, 4567–4590.
11. Zhang, H.; Chen, M.-G.; Lian, C.-X.; Yuan, W.-C.; Zhang, X.-M. Synlett 2010,
1415–1417.
12. Zeng, X.-F.; Ji, S.-J.; Wang, S.-Y. Tetrahedron 2005, 61, 10235–10241.
13. Xia, M.; Wang, S. H.; Yuan, W. B. Synth. Commun. 2004, 34, 3175–3182.
14. Feng, X. L.; Zhang, Y.; Lin, Z. H.; Zhao, C. X.; Chow, T. Heterocycl. Commun. 2005,
11, 427–432.
15. (a) Feng, X.-L.; Guan, C.-J.; Zhao, C.-X. J. Chem. Res., Synop 2003, 744–745; (b)
Lin, Z.-H.; Guan, C.-J.; Feng, X.-L.; Zhao, C.-X. J. Mol. Catal. A: Chem. 2006, 247,
19–26.
16. Selected chiral Friedel–Crafts amidoalkylations see: (a) Johannsen, M. Chem.
Commun. 1999, 2233–2334; (b) Jia, Y.-X.; Xie, J.-H.; Duan, H.-F.; Wang, L.-X.;
Zhou, Q.-L. Org. Lett. 2006, 8, 1621–1624; (c) Esquivias, J.; Arrayás, R. G.;
Carretero, J. C. Angew. Chem. 2006, 118, 645–649. Angew. Chem., Int. Ed., 2006,
45, 629–633; (d) Wang, Y. Q.; Song, J.; Hong, R.; Li, H.; Deng, L. J. Am. Chem. Soc.
2006, 128, 8156–8157; (e) Kang, Q.; Zhao, Z.-A.; You, S.-L. J. Am. Chem. Soc.
2007, 129, 1484–1485; (f) Terada, M.; Yokoyama, S.; Sorimachi, K.; Uraguchib,
D. Adv. Synth. Catal. 2007, 349, 1863–1867; (g) Rowland, G. B.; Rowland, E. B.;
Antilla, J. C. Org. Lett. 2007, 9, 2609–2611; (h) Alonso, I.; Esquivias, J.; Arrayás, R.
G.; Carretero, J. C. J. Org. Chem. 2008, 73, 6401–6404.
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.tetlet.2011.07.010.
References and notes
1. Selected book chapters and publications, see: (a) Atta-ur-Rahman; Basha, A.
Indole Alkaloids; Harwood Academic: Chichester, UK, 1998; (b) Kutney, J. P. The
synthesis of indole alkaloids In The Total Synthesis of Natural Products; ApSimon,
J., Ed.; Wiley-Interscience: New York, 1977; Vol. 3, pp 273–276; (c) Shiri, M.;
Zolfigol, M. A.; Kruger, H. G.; Tanbakouchian, Z. Chem. Rev. 2010, 110, 2250–
2293; (d) Ke, B.; Qin, Y.; He, Q.; Huang, Z.; Wang, F. Tetrahedron Lett. 2005, 46,
1751; (e) He, Q.-L.; Sun, F.-L.; You, S.-L. Synlett 2009, 1111–1114; (f) Bandini,
17. Shirakawa, S.; Kobayashi, S. Org. Lett. 2006, 8, 4939–4942.
18. Pan, S. C.; List, B. Chem. Asian J. 2008, 3, 430–437.