Highly efficient asymmetric organocatalytic Friedel-Crafts alkylation of indoles with α,β-unsaturated aldehydes

Article abstract of DOI:10.1039/c0ob00016g

The development of an improved organocatalyst, N-isopropylated bipyrrolidine 2a, for the asymmetric Friedel-Crafts alkylation of indoles with α,β-unsaturated aldehydes has been presented. The new organocatalyst readily facilitates the enantioselective alk

Full text of DOI:10.1039/c0ob00016g

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PAPER
www.rsc.org/obc | Organic & Biomolecular Chemistry
Highly efficient asymmetric organocatalytic Friedel–Crafts alkylation of
indoles with a,b-unsaturated aldehydes†
Shangbin Jin,a Chenguang Li,a Yuanhui Ma,a Yuhe Kan,b Yong Jian Zhang*a and Wanbin Zhang*a
Received 18th April 2010, Accepted 11th June 2010
First published as an Advance Article on the web 9th July 2010
DOI: 10.1039/c0ob00016g
The development of an improved organocatalyst, N-isopropylated bipyrrolidine 2a, for the asymmetric
Friedel–Crafts alkylation of indoles with a,b-unsaturated aldehydes has been presented. The new
organocatalyst readily facilitates the enantioselective alkylation reaction, providing 3-alkylated indoles
in good to high yields (62–89%) with high levels of enantioselectivity (80–93% ee) using only 2 mol% of
catalyst loading.
Most recently, we reported new bipyrrolidine organocatalyst 1
(Fig. 1) which was successfully applied in asymmetric Diels–Alder
reactions of a,b-unsaturated aldehydes.12 It was demonstrated
that the 3,3¢-dibenzyloxy groups of catalyst 1 play a significant
role in acceleration of the reaction rate in the Diels–Alder
Introduction
During the past decade organocatalysis has witnessed an explosive
growth in the field of asymmetric synthesis since it employs small
organic molecules that are relatively non-toxic, inexpensive and
stable to both air and moisture.1 Organocatalysis has become the
reaction. In our continuing effort to develop a highly active
third main branch in catalytic asymmetric synthesis, together with
organocatalytic system, in this paper we document the efficient
enzymatic and organometallic catalysis, and a great number of
new asymmetric transformations have been developed using small
organic molecules as catalysts. However, in most organocatalytic
asymmetric organocatalytic Friedel–Crafts alkylation of indoles
with a,b-unsaturated aldehydes using N-modified bipyrrolidines
2 (Fig. 1) as catalysts. Although N-isopropylated bipyrrolidine has
reactions toachievereasonable reactionrates, highcatalystloading
been revealed as an efficient organocatalyst for many asymmetric
reactions,13 there are no reports concerning its use as a chiral
catalyst in iminium catalysis. Significantly, using only 2 mol% of
our improved organocatalyst N-isopropylated bipyrrolidine 2a,
the Friedel–Crafts alkylation reaction afforded 3-alkylated indoles
in good to high yields with high level of enantioselectivities.
is generally required. Therefore, the development of highly active
organocatalysts aiming to lower catalyst loadings is an important
challenge.
The asymmetric Friedel–Crafts reaction is one of the most
powerful methods for synthesis of optically active aromatic
compounds.2 Based on the strategy of LUMO-lowering activation
of a,b-unsaturated aldehydes, MacMillan and co-workers first
explored organocatalytic asymmetric Friedel–Craft alkylation of
pyrroles and indoles.3 Since then, MacMillan’s imidazolidinone
catalysts have also been used for indole alkylation with cyclic,4
(E)-dialkyl 3-oxoprop-1-enylphosphonates5 and g-hydroxy a,b-
unsaturated aldehyde6 as well as the intramolecular Friedel–Crafts
alkylation of indoles.7 Bonini and co-workers reported indole
alkylation reactions with aziridin-2-yl methanols as catalysts, how-
ever, the enantioselectivity is not sufficiently high.8 Most recently,
Wang and Bao independently reported these transformations
catalyzed by chiral diphenylprolinol trimethylsilyl ether without
acid co-catalyst.9 Lee and co-workers reported camphor sulfonyl
hydrazine-catalyzed asymmetric indole alkylation reactions.10 In
spite of the further improvements in this type of organocatalytic
Friedel–Crafts alkylation of indoles with a,b-unsaturated ketones
have been reported,11 higher catalyst loading (10–30 mol%)
remains a main drawback for this important transformation.
Fig. 1 Structure of bipyrrolidine catalysts 1 and 2.
Results and discussion
The new bipyrrolidine catalysts 2 were readily prepared from
bipyrrolidine 1 and ketones or aldehydes via reductive amination
process. As shown in Scheme 1, the monoalkylation of 1,2-
diamines consists of the formation of intermediate aminals from
aldehydes or ketones followed by their reduction with sodium
borohydride.13a According to this general procedure several
aSchool of Chemistry and Chemical Engineering, Shanghai Jiao Tong
University, Shanghai, 200240, P. R. China. E-mail: yjian@sjtu.eud.cn;
Fax: 86-21-5474-3265; Tel: 86-21-5474-0787
bSchool of Chemistry and Chemical Engineering, Huaiyin Normal University,
Huaian, Jiangshu, 223300, P. R. China
† Electronic supplementary information (ESI) available: 1H NMR and 13
C
NMR spectra of all new synthesized compounds, and HPLC traces for
enantioselectivity determination. See DOI: 10.1039/c0ob00016g
Scheme 1 Preparation of N-substituted bipyrrolidines 2
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Table 1 Optimization of reaction conditionsa
Table 2 Effect of catalyst loading on the alkylation reactiona
Yield (%)b
ee (%)c
Entry
Cat.
X
Solvent
T/h
Yield (%)b
ee (%)c
Entry
X
T/h
1
2
3
4
5
6
7
8
1
20
20
—
10
30
40
20
20
20
20
20
20
20
20
20
20
20
CH2Cl2/iPrOH
CH2Cl2/iPrOH
CH2Cl2/iPrOH
CH2Cl2/iPrOH
CH2Cl2/iPrOH
CH2Cl2/iPrOH
CH2Cl2
CH3Cl
iPrOH
EtOH
MeOH
MeOH–H2O
THF
Et2O
CH3CN
DMF
NMP
48
2
24
5
2
2
24
14
2
2
2
2
12
5
14
2
24
49
85
NR
81
49
38
11
77
85
89
90
90
95
67
16
70
65
55
76
—
72
73
66
7
31
76
74
76
68
58
52
7
1
2
3
10
5
2
2
4
4
90
87
80
88
90
90
2a
2a
2a
2a
2a
2a
2a
2a
2a
2a
2a
2a
2a
2a
2a
2a
a The reactions were carried out with 0.5 mmol of indole, 1.5 mmol
of crotonaldehyde in methanol (2.0 mL, 0.25 M). b Isolated yield after
purification by column chromatography on silica gel. c Determined by
chiral HPLC. Absolute configurations determined by comparison with
literature data.
9
10
11
12
13
14
15
16
17
Table 3 Asymmetric Friedel–Crafts alkylation of indole (3a) with (E)-2-
hexenal (4b)
75
74
a The reactions were carried out with 0.5 mmol of indole, 1.5 mmol
of crotonaldehyde, 0.05 mmol of bipyrrolidine, and 0.10 mmol of
TfOH in solvent (2.0 mL, 0.25 M). b Isolated yield after purification by
column chromatography on silica gel. c Determined by chiral HPLC. Ab-
solute configurations determined by comparison with literature data.
CH2Cl2/iPrOH = 85/15 (v/v); MeOH–H2O = 19/1 (v/v); NMP = N-
methyl-2-pyrrolidinone. NR = no reaction.
Entry
Bipyrr.
Acid
T/h
Yield (%)b
ee (%)c
1
2
3
4
5
6
7
8
9d
2a
2a
2a
2a
2a
2b
2c
2d
2a
TfOH
HClO4
TFA
p-TSA
p-NO2BzOH
TfOH
TfOH
TfOH
TfOH
4
5
20
24
24
7
7
7
36
80
80
79
trace
trace
81
70
80
90
90
86
—
—
89
90
86
92
mono-N-alkylated bipyrrolidines 2 were synthesized starting from
bipyrrolidine 1 (40–74% yields).
A model experiment was conducted with indole (3a) and (E)-
crotonaldehyde (4a) in the presence of 10 mol% of bipyrrolidine
1 and 20 mol% of TfOH as cocatalyst in methylene chloride and
88
a The reactions were carried out with 0.5 mmol of indole, 1.5 mmol
of hexenal, 0.01 mmol of bipyrrolidine, and 0.02 mmol of acid in
MeOH (2.0 mL, 0.25 M). b Isolated yield after purification by column
chromatography on silica gel. c Determined by chiral HPLC. Absolute
configurations determined by comparison with literature data. d The
reaction was carried out at -45 ◦C.
◦
isopropanol (v/v = 85/15) at -25 C. As shown in Table 1, the
reaction gave 3-alkylated indole 5a in only 49% yield with 55%
ee for 48 h (entry 1). Interestingly, when using N-isopropylated
bipyrrolidine 2a as catalyst, the reaction remarkably improved.
The alkylation reaction with 10 mol% of 2a as a catalyst afforded
5a in 85% isolated yield with 76% ee within only 2 h (entry 2).
The amounts of the acid co-catalyst had large effects on the
reaction. The reaction without acid additive did not proceed at
all (entry 3). When the reaction was performed with 10 mol% of
TfOH, the enantioselectivity slightly decreased (entry 4). Upon
further increasing of the dosage of acid co-catalyst, the reaction
efficiencies were remarkably decreased (entries 5 and 6). The results
demonstrated that the diammonium salt of bipyrrolidine 2a is
the best catalytic species for the reaction. With 10 mol% of N-
isopropylated bipyrrolidine 2a and 20 mol% of TfOH, different
reaction solvents were screened (entries 7–17). It was found that
the alkylation reaction largely depended on the solvent. The
results indicated that CH2Cl2, CH3Cl, Et2O, THF and CH3CN
are unsuitable solvents for the reaction (entries 7, 8, 13–15). Protic
solvents are better for the reaction (entries 9–12) and methanol is
the best solvent (entry 11).
was performed in methanol at -25 ◦C, it was found that catalyst
loadings as low as 2 mol% provide alkylated product 5b in high
isolated yield (80%) with useful levels of enantioselectivity (90%
ee) within 4 h.
To further improve the reaction, the effect of acid co-catalyst
on reaction efficiency was investigated (Table 3). The Brønsted
acid co-catalyst had large effects on the reaction (entries 1–5).
When using HClO4 as cocatalyst, the reaction gave similar results
as with TfOH (entry 2). When the reaction was performed with
trifluoroacetic acid (TFA), a longer reaction time was needed
(entry 3). However, only trace amounts of products were observed
using p-toluenesulfonic acid (p-TSA) or p-nitrobenzoic acid as
co-catalysts (entries 4 and 5). Further tuning of N-substituent
of catalyst 2 did not improve the enantioselectivity (entries 6–8).
However, when the reaction temperature was decreased to -45 ◦C,
the reaction gave 3-substituted indole 5b in 88% isolated yield with
92% ee (entry 9).
Encouraged by these initial results, the effect of catalyst loading
on reaction efficiency was evaluated (Table 2). When the Friedel–
Crafts alkylation reaction of indole (3a) with (E)-2-hexenal (4b)
With optimized conditions in hand, the scope of the
Friedel–Crafts alkylations of substituted indoles with various
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Table 4 Organocatalytic Friedel–Crafts alkylation of indoles 3 with
a,b-unsaturated aldehydes 4a
To elucidate the origin of asymmetric induction, the lowest
energy conformer of iminium ion 6 formed from catalyst 2a and
2-hexenal was calculated (Fig. 2, DFT calculation at B3LYP/6-
31g(d) level). Inspection of the structure of intermediate 6
reveals (i) selective formation of the (E)-iminium isomer to avoid
nonbonding interactions between the substrate olefin and the
pyrrolidine group at the other side, (ii) the N-isopropyl group
effectively shields the Re-face of the iminium ion, leaving the Si-
face exposed to indole attack, and (iii) two benzyloxy groups on
the catalyst likely further restrict conformational flexibility having
a positive effect on the enantioselectivity.
3a, R = H; 3b, R = 1-Me;
4a, R¢ = Me; 4b, R¢ = nPr; 4c, R¢ = Et;
3c, R = 1-Bn; 3d, R = 1-allyl; 4d, R¢ = CH2OBz; 4e, R¢ = COOEt
3e, R = 5-OMe; 3f, R = 5-Br
Fig. 2 Minimum energy iminium ion 6 formed from 2a and 2-hexenal.
Conclusion
In conclusion, we have documented our development of an
improved organocatalyst N-isopropylated bipyrrolidine 2a for
the asymmetric Friedel–Crafts alkylation of indoles with a,b-
unsaturated aldehydes. The new organocatalyst readily facilitates
the enantioselective alkylation reaction, providing 3-alkylated
indoles in good to high yields (62–89%) with high levels of
enantioselectivity (80–93% ee) using only 2 mol% of catalyst
loading. Further studies on development of new organocat-
alytic transformations aiming to lower catalyst loading will be
forthcoming.
a Yields are of alkylated products isolated by column chromatography on
silica gel. Enantiomeric excess was determined by chiral stationary phase
HPLC analysis. See the ESI† for further details. b The reaction was carried
out at -25 ◦C.
Experimental
All reactions were run under an atmosphere of nitrogen, unless
otherwise indicated. Dry solvents were purified according to the
standard method. Indoles were recrystallized before use. a,b-
Unsaturated aldehydes were distilled and stored under nitrogen
a,b-unsaturated aldehydes was explored using 2 mol% of 2a and
4 mol% of TfOH as co-catalyst (Table 4). Reactions of indole
3a with functionalized a,b-unsaturated aldehydes afforded 3-
alkylated indoles 5a–5e in high isolated yields (71–89%) with
good to excellent enantioselectivities (80–92% ee). Substituted
indoles were subjected to alkylation with 2-hexenal giving prod-
ucts 5f–5j in good to high yields (62–88%) with high level of
enantioselectivities (89–93% ee). Notably, the yields and enan-
tioselectivities of the alkylation reactions obtained with only 2
mol% of N-isopropylated bipyrrolidine 2a are comparable to those
obtained with former catalytic systems, requiring higher catalyst
loading.3–10
◦
1
atmosphere at -20 C. H NMR spectra were measured on a
MERCURY plus400 (400 MHz) spectrometer. Chemical shifts
are reported in ppm from tetramethylsilane as an internal stan-
dard. Data are reported as follows: chemical shift, integration,
multiplicity, coupling constants (Hz), and assignment. 13C NMR
spectra were recorded on a MERCURY plus400 (100 MHz)
spectrometer with complete proton decoupling. Chemical shifts
are reported in ppm from the residual solvent as an internal
R
standard. Optical rotations were taken on a SGWꢀ-1 automatic
polarimeter. High performance liquid chromatography (HPLC)
was performed on Class-Vp6x, Single ee using a Daicel Chiralcel
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AD-H, OD-H, or AS-H. Mass spectra were recorded by EI
and ESI, and HRMS were measured on a HP-5989 instrument.
For thin layer chromatography (TLC) analysis throughout this
work, TLC plates were used. TLC spots were visualized under
ultraviolet light or developed by heating after treatment with
potassium permanganate. The products were purified by flash
column chromatography on silica gel (100–200 mesh).
(2S,2¢S,3R,3¢R)-1-benzyl-3,3¢-bis(benzyloxy)-2,2¢-bipyrrolidine
(2c)
In accordance with the general procedure, the reaction was carried
out in the presence of benzaldehyde (73.0 mL, 0.71 mmol) in diethyl
ether (10 mL) as solvent to afford title compound 2c as a yellowish
oil (126 mg, 40% yield). [a]2D5 = -38.6 (c = 0.60, EtOH); 1H
NMR (400 MHz, CDCl3) d 7.37–7.20 (m, 15H), 4.50 (dd, J =
2.4, 12.0 Hz, 2H), 4.38 (dd, J = 12.0, 14.0 Hz, 2H), 4.07 (d,
J = 13.6 Hz, 1H), 3.90–3.87 (m, 1H), 3.80–3.75 (m, 1H), 3.54 (d,
J = 12.8 Hz, 2H), 3.09 (dd, J = 4.4, 5.2 Hz, 1H), 3.03–2.87 (m,
4H), 2.62–2.54 (m, 1H), 2.02–1.58 (m, 4H); 13C NMR (100 MHz,
CDCl3) d 139.9, 138.6, 138.4, 128.9, 128.8, 128.7, 128.6, 128.5,
128.0, 127.9, 127.9, 127.3, 83.0, 81.6, 71.4, 71.2, 70.7, 67.3, 61.7,
53.1, 44.9, 32.5, 30.8; HRMS (ESI-TOF) Calcd. For C29H34N2O2
[M+H] 443.2699, Found: 443.2690;
General procedure for the synthesis of catalyst 2
To a solution of bipyrrolidine 1 (250 mg, 0.71 mmol) in solvent
˚
(10 mL) was added activated 4 A molecular sieves, and ketone or
aldehyde (0.71 mmol). The reaction mixture was stirred overnight
at ambient temperature, and then K2CO3 was added and stirred for
1 h. The precipitate was filtered and the filtrate was concentrated to
give the crude aminal which was used without further purification.
To a solution of the aminal in MeOH (10 mL) was added NaBH4
(40 mg, 1.07 mmol) at 0 ◦C. After stirring for 10 min, acetic acid
(0.12 mL, 2.13 mmol) was added and the mixture was stirred for
4 h. The reaction was quenched by 5 mL of 30% NaOH aqueous
solution and extracted with ethyl acetate (20 mL ¥ 3). The organic
layer was washed with brine, dried over K2CO3, filtered, and the
solvent was removed in vacuo. The obtained residue was purified
by column chromatography on silica gel (ethyl acetate : petroleum
ether = 1 : 4, 5% Et3N) to afford N-alkylated bipyrrolidine 2.
(2S,2¢S,3R,3¢R)-3,3¢-bis(benzyloxy)-1-(3-phenylpropyl)-2,2¢-
bipyrrolidine (2d)
In accordance with the general procedure, the reaction was carried
out in the presence of 3-phenylpropanal (94.3 mL, 0.71 mmol)
in diethyl ether (10 mL) as solvent to afford title compound 2d
as a yellowish oil (184 mg, 55% yield), [a]2D5 = -14.8 (c = 0.24,
EtOH); 1H NMR (400 MHz, CDCl3) d 7.37–7.23 (m, 12H), 7.20–
7.14 (m, 3H), 4.51–4.36 (m, 3H), 4.28 (d, J = 11.6 Hz, 1H),
3.85 (d, J = 5.2 Hz, 1H), 3.70–3.64 (m, 1H), 3.16–3.08 (m, 1H),
2.97–2.89 (m, 3H), 2.84–2.74 (m, 2H), 2.70–2.60 (m, 1H), 2.59–
2.45 (m, 3H), 1.97–1.66 (m, 6H); 13C NMR (100 MHz, CDCl3)
d 142.5, 138.8, 138.7, 128.6, 128.6, 128.5, 128.0, 127.8, 127.8, 127.7,
82.8, 81.7, 72.2, 71.4, 70.4, 68.4, 57.3, 52.6, 45.2, 33.7, 32.9, 30.9,
30.7; HRMS (ESI-TOF) Calcd. for C31H38N2O2 [M+H] 470.2933,
Found: 470.2938.
(2S,2¢S,3R,3¢R)-3,3¢-bis(benzyloxy)-1-isopropyl-2,2¢-bipyrrolidine
(2a)
In accordance with the general procedure, the reaction was carried
out in acetone (10 mL) as solvent to afford title compound 2a as a
yellowish oil (207 mg, 74% yield). [a]2D5 = +19.0 (c = 0.20, EtOH);
1H NMR (400 MHz, CDCl3) d 7.35–7.21 (m, 10H), 4.50 (d, J =
12.0 Hz, 1H), 4.43 (s, 2H), 4.35 (d, J = 12.0 Hz, 1H), 3.83–3.80
(m, 1H), 3.74–3.69 (m, 1H), 3.03–2.76 (m, 7H), 1.92–1.72 (m, 4H),
1.65 (s, 1H), 1.08 (d, J = 6.0 Hz, 3H), 0.97 (d, J = 6.0 Hz, 3H);
13C NMR (100 MHz, CDCl3) d 128.6, 128.1, 127.8, 127.7, 127.6,
82.4, 81.7, 71.3, 70.2, 68.8, 68.0, 51.2, 45.2, 44.0, 33.0, 30.8, 23.0,
15.1; HRMS (EI-TOF) calcd for C25H34N2O2 394.2620, Found:
394.2629.
General procedure for the asymmetric Friedel–Crafts alkylation
reaction
To a stirred solution of catalysts 2a (0.01 mmol, 3.9 mg) and TfOH
(0.02 mmol, 1.8 mL) in MeOH (2 mL) was added a,b-unsaturated
aldehyde (1.5 mmol) at -45 ◦C. The solution was stirred for 10 min
before indole (0.5 mmol) was added. The reaction mixture was
stirred at -45 ◦C for 36–64 h and warmed to ambient temperature.
The reaction was quenched by saturated NaHCO3, extracted with
CH2Cl2 (5 mL ¥ 3) and washed with brine. The organic layer
was dried by anhydrous Na2SO4, filtered, and the solvent was
removed in vacuo. The residue was purified by silica gel column
chromatography (ethyl acetate : petroleum ether = 1 : 6) to afford
the corresponding 3-alkylated indole. To determine enantiomeric
excess, the product was converted to the corresponding alcohol
with NaBH4 in MeOH and enantiomeric excess was determined
by HPLC using a Chiracel AD-H, OD-H, or AS-H. See the ESI†
for further details.
(2S,2¢S,3R,3¢R)-3,3¢-bis(benzyloxy)-1-cyclohexyl-2,2¢-
bipyrrolidine (2b)
In accordance with the general procedure, the reaction was carried
out in the presence of cyclohexenone (73.5 mL, 0.71 mmol) in THF
(10 mL) as solvent to afford title compound 2b as a yellowish oil
1
(139 mg, 45% yield). [a]2D5 = +4.4 (c = 1.2, EtOH); H NMR
(400 MHz, CDCl3) d 7.34–7.23 (m, 10H), 4.49 (d, J = 11.6 Hz,
1H), 4.42 (d, J = 2.8 Hz, 2H), 4.35 (d, J = 11.6 Hz, 1H), 3.85–3.81
(m, 1H), 3.73–3.68 (m, 1H), 3.09 (d, J = 6.0 Hz, 1H), 3.01–2.84
(m, 5H), 2.63–2.52 (m, 1H), 1.82–1.69 (m, 6H), 1.61 (m, J =
11.6 Hz, 1H), 1.36–0.97 (m, 7H); 13C NMR (100 MHz, CDCl3)
d 138.8, 138.6, 128.6, 128.6, 128.0, 127.8, 127.7, 82.0, 81.8, 71.3,
70.3, 68.2, 68.1, 61.0, 45.7, 45.2, 33.6, 33.0, 30.9, 26.6, 26.5, 26.0,
25.9; HRMS (ESI-TOF) Calcd. For C28H38N2O2 [M+H] 435.3012,
Found: 435.3021.
Acknowledgements
This research was supported by the National Natural Science
Foundation of China, and Shanghai Jiao Tong University (Chenx-
ing Program).
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5 Y. C. Guo, D.-P. Li, Y.-L. Li, H.-M. Wang and W.-J. Xiao, Chirality,
2009, 21, 777.
Notes and references
1 For selected recent reviews on asymmetric organocatalysis, see:
(a) A. Berkessel and H. Groger, Asymmetric Organocatalysis: From
Biomimetic Concepts to Applications in Asymmetric Synthesis, Wiley-
VCH, Weinheim, 2005; (b) P. I. Dalko, Enantioselective Organocatalysis,
Wiley-VCH, Weinheim, 2007; (c) B. List and J. W. Yang, Science, 2006,
313, 1584; (d) D. W. C. MacMillan, Nature, 2008, 455, 304; (e) A.
Dondoni and A. Massi, Angew. Chem., Int. Ed., 2008, 47, 4638; (f) J. B.
Brazier and N. C. O. Tomkinson, in Asymmetric Organocatalysis:
Topics in Current Chemistry, ed. B. List, Springer, 2010, 291, 281–347.
2 For selected reviews on asymmetric Friedel–Crafts reactions: (a) M.
Bandini, A. Melloni and A. Umani-Ronchi, Angew. Chem., Int. Ed.,
2004, 43, 550; (b) M. Bandini, A. Melloni, S. Tommasi and A. Umani-
Ronchi, Synlett, 2005, 1199; (c) T. Poulsen and K. A. Jørgensen, Chem.
Rev., 2008, 108, 2903; (d) S.-L. You, Q. Cai and M. Zeng, Chem.
Soc. Rev., 2009, 38, 2190; (e) E. Marque´s-Lo´pez, A. Diez-Martinez,
P. Merino and R. P. Herrera, Curr. Org. Chem., 2009, 13, 1585; (f) M.
Bandini and A. Umani-Ronchi, Catalytic Asymmetric Friedel–Crafts
Alkylations, Wiley-VCH, Weinheim, 2009; (g) V. Terrasson, R. M. De
Figueiredo and J. M. Campagne, Eur. J. Org. Chem., 2010, 14, 2635.
3 (a) N. A. Paras and D. W. C. MacMillan, J. Am. Chem. Soc., 2001, 123,
4370; (b) J. F. Austin and D. W. C. MacMillan, J. Am. Chem. Soc., 2002,
124, 1172.
6 S.-G. Kim, Bull. Korean Chem. Soc., 2009, 30, 2519.
7 C.-F. Li, H. Liu, J. Liao, Y.-J. Cao, X.-P. Liu and W.-J. Xiao, Org. Lett.,
2007, 9, 1847.
8 B. F. Bonini, E. Capito`, M. Comes-Franchini, M. Fochi, A. Ricci and
B. Zwanenburg, Tetrahedron: Asymmetry, 2006, 17, 3135.
9 (a) L. Hong, L. Wang, C. Chen, B. Zhang and R. Wang, Adv. Synth.
Catal., 2009, 351, 772; (b) L. Hong, C. Liu, W. Sun, L. Wang, K. Wong
and R. Wang, Org. Lett., 2009, 11, 2177; (c) Z.-J. Wang, J.-G. Yang, J.
Jin, X. Lv and W. Bao, Synthesis, 2009, 3994.
10 T. Tian, B.-J. Pei, Q.-H. Li, H. He, L.-Y. Chen, X. Zhou, W.-H. Chan
and A. W. M. Lee, Synlett, 2009, 2115.
11 (a) D.-P. Li, Y.-C. Guo, Y. Ding and W.-J. Xiao, Chem. Commun., 2006,
799; (b) W. Chen, W. Du and Y. C. Chen, Org. Biomol. Chem., 2007, 5,
816; (c) G. Bartoli, M. Bosco, A. Carlone, F. Pesciaioli, L. Sambri and
P. Melchiorre, Org. Lett., 2007, 9, 1403.
12 (a) Y. Ma, Y. J. Zhang, S. Jin, Q. Li, C. Li, J. Lee and W. Zhang,
Tetrahedron Lett., 2009, 50, 7388; (b) Y. Ma, S. Jin, Y. Kan, Y. J. Zhang
and W. Zhang, Tetrahedron, 2010, 66, 3849.
13 For selected examples, see:(a) A. Alexakis and O. Andrey, Org. Lett.,
2002, 4, 3611; (b) O. Andrey, A. Alexakis and G. Bernardinelli, Org.
Lett., 2003, 5, 2559; (c) O. Andrey, A. Alexakis, A. Tomassini and G.
Bernardinelli, Adv. Synth. Catal., 2004, 346, 1147; (d) S. Mosse and A.
Alexakis, Org. Lett., 2005, 7, 4361; (e) S. Sulzer-Mosse, M. Tissot and
A. Alexakis, Org. Lett., 2007, 9, 3749.
4 H. D. King, Z. Meng, D. Denhart, R. Mattson, R. Kimura, D. Wu, Q.
Gao and J. E. Macor, Org. Lett., 2005, 7, 3437.
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