Highly enantioselective diels-alder reaction catalyzed by chiral imidazolidinone

Article abstract of DOI:10.1080/00397910802632571

New chiral imidazolidinone with an indole group was synthesized and used to catalyze the Diels-Alder reaction of α,β-unsaturated aldehyde with diene. High enantiomeric excesses and good yields were obtained. The reaction media were also surveyed. The best

Full text of DOI:10.1080/00397910802632571

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Highly Enantioselective
Diels–Alder Reaction Catalyzed
by Chiral Imidazolidinone
a
b
b
Yongjiang Wang , Xiaoliang Xu & Wen Pei
a
Key Laboratory of Agricultural Products Chemical
and Biological Processing Technology of Zhejiang
Province, School of Biological and Chemical
Engineering, Zhejiang University of Science and
Technology, Hangzhou, China
b
College of Chemical Engineering and Material
Science, Zhejiang University of Technology,
Hangzhou, China
Version of record first published: 27 Apr 2009.
To cite this article: Yongjiang Wang , Xiaoliang Xu & Wen Pei (2009): Highly
Enantioselective Diels–Alder Reaction Catalyzed by Chiral Imidazolidinone, Synthetic
Communications: An International Journal for Rapid Communication of Synthetic
Organic Chemistry, 39:11, 2032-2041
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1
Synthetic Communications , 39: 2032–2041, 2009
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397910802632571
Highly Enantioselective Diels–Alder Reaction
Catalyzed by Chiral Imidazolidinone
1
2
2
Yongjiang Wang, Xiaoliang Xu, and Wen Pei
Key Laboratory of Agricultural Products Chemical and Biological
1
Processing Technology of Zhejiang Province, School of Biological and
Chemical Engineering, Zhejiang University of Science and Technology,
Hangzhou, China
2
College of Chemical Engineering and Material Science, Zhejiang
University of Technology, Hangzhou, China
Abstract: New chiral imidazolidinone with an indole group was synthesized and
used to catalyze the Diels–Alder reaction of a,b-unsaturated aldehyde with diene.
High enantiomeric excesses and good yields were obtained. The reaction media
were also surveyed. The best result in terms of enantioselectivity was achieved
3 2
using acrolein and 2,3-dimethylbutdiene (up to 95% ee) in CH OH=H O.
Keywords: Catalyst, Diels–Alder reaction, imidazolidinone, a,b-unsaturated
aldehyde
INTRODUCTION
The control of absolute stereochemistry in the Diels–Alder reaction, one
of the most important methods for construction of cyclohexene deriva-
[1]
tives, has been studied extensively. In our previous study, we reported
the highly enantioselective Diels–Alder reactions between dienes and
[
2]
1
-phenylsulfonyl-3-alken-2-ones employing chiral Lewis acid catalyst.
Our recent interest in asymmetric Diels–Alder reactions has been
focused on asymmetric organocatalytic transformations because of the
Received August 28, 2008.
Address correspondence to Wen Pei, College of Chemical Engineering and
Material Science, Zhejiang University of Technology, Hangzhou 310 014, China.
E-mail: river0301@163.com
2
032

New Chiral Imidazolidinone
2033
Figure 1. Chiral secondary amine hydrochloride derived from amino acids.
advantages associated with the use of small organic molecules as chiral
[
catalysts.
3]
The first highly enantioselective organocatalyzed Diels–Alder reac-
tion of a,b-unsaturated aldehydes to dienes using chiral secondary amine
[
4]
derived from S-phenylalanine was achieved by Ahrendt et al. The role
of neighboring p-electron-rich aromatic groups to channel the Diels–
Alder reactions along a specific stereochemical pathway led us to a study
of L-tryptophan derivative as a catalyst for enantioselective Diels–Alder
reactions because the indole ring has strong p-electron-donating
[
5]
character.
In this work, we report a new organocatalyst 3. The catalyst syn-
thesized from L-tryptophan was a chiral secondary amine hydrochloride,
which can react with aldehydes to generate active iminium ions (Fig. 1).
RESULTS AND DISCUSSION
Our enantioselective catalytic Diels–Alder reaction was first evaluated
using cyclopentadiene with (E)-cinnamaldehyde and three kinds of chiral
secondary amine hydrochlorides. As revealed in Table 1, the Diels–Alder
adduct was obtained in excellent yield but poor stereoselectivity (entry 1,
8
4%, 2.9:1 exo=endo, exo 30% ee) by using a catalytic quantity of trans-4-
hydroxy-L-proline ethyl ester (10 mol%). With the (S)-proline methyl
ester, an increase in enantio- control was observed (entry 2, 80% yield,
2
.7:1 exo=endo, 48% ee). Importantly, control of iminium ion geometry
through the use of steric constraints on the catalyst architecture 3 was
found to provide the best levels of enantioselectivity (93% ee) while main-
taining reaction efficiency (entry 3, 5.0 mol%). Consequently, amine salt 3
was identified as the optimal catalyst for further exploration.
The reaction media for this organocatalytic Diels–Alder reaction
were examined. We selected weak polar solvents such as toluene, dichloro-
methane (DCM), tetrahydrofuran (THF), and strong ones including
water and room temperature ion liquids (RTIL). Interestingly, as

2034
Y. Wang, X. Xu, and W. Pei
Table 1. Organocatalyzed Diels–Alder reaction between cinnamaldehyde and
cyclopentadiene
a
b,c
Entry
Catalyst
Time (h)
Yield (%)
Exo=endo
Exo ee (%)
1
2
3
1
2
3
24
24
12
84
80
99
2.9:1
2.7:1
1:1
30 (5R,6R)
48 (5R,6R)
93 (5S,6S)
d
a
Isolated yield.
b
Product ratios determined by GLC using an RTX-13100 column.
Absolute and relative configurations were determined by correlation to the
literature. .
d
Using 5.0 mol% catalyst.
c
[
4,6,7]
revealed in Table 2, the Diels–Alder reaction could be conducted
smoothly both in [bmim]BF and [bmim]PF with excellent yield and
4
6
high stereoselectivity (entry 5: 95%, 1:1 exo=endo, exo 86% ee, endo
8% ee; entry 6: 94%, 1.3:1 exo=endo, exo 66% ee, endo 68% ee). The
use of CH OH=H O provided optimal selectivity and chemical yield
8
3
2
Table 2. Effect of the polarity of solvent on the asymmetric Diels–Alder reaction
of cinnamaldehyde and cyclopentadiene
b
a
Time (h) Yield (%) Exo=endo Exo=% ee Endo=% ee
Entry Solvent
1
2
3
4
5
6
7
THF
CH Cl2
Toluene
48
48
48
48
24
24
12
<10
<10
<10
<10
95
—
—
—
—
1:1
1.3:1
1:1
—
—
—
—
86
66
93
—
—
—
—
88
68
90
2
2
H O
[bmim]BF4
[bmim]PF
CH OH=H
6
94
99
3
2
O
a
Enantiomeric excess and exo=endo determined by chiral GLC analysis (RTX-
3100 column).
Isolated yield.
1
b

New Chiral Imidazolidinone
2035
(
entry 7, 99% yield, 1:1 exo=endo, exo 93% ee, endo 90% ee). However,
the organocatalytic Diels–Alder reaction of cyclopentadiene with (E)-cin-
namaldehyde in weak polar solvents and water was not very efficient with
respect to stereoselectivity and yield. The superior levels of asymmetric
induction and efficiency exhibited by amine salt 3 in CH OH=H O at
3
2
room temperature to afford exo cycloadduct in 93% ee prompted us to
select these catalytic conditions for further exploration.
Experiments that probe the scope of the Diels–Alder reaction com-
ponent are summarized in Table 3. Variation of the olefin substituent
(
R ¼ Me, Ph. 2-furyl, entries 1–3) is possible without loss in yield or
Table 3. Organocatalyzed Diels–Alder reaction between different dienophiles and
representative dienes
Time Yield Dr
a
f
(exo=endo) ee (%)
Entry
1
R
Diene Product
(h)
(%)
b
d
Me
18
77
99
1.3:1
1:1
91 (5R,6S)
b
d
2
3
Ph
12
24
93 (5S,6S)
89 (5S,6S)
b
d
2-Furyl
90
1:1.1
c
e
4
H
H
24
24
83
89
—
86 (R)
c
—
e
5
95 (R)
a
Isolated yield.
Product ratios determined by GLC using an RTX-13100 column.
b
c
Product ratios determined by HPLC using an AS-H column.
d
Absolute configuration of exo.
Absolute configuration of para.
Absolute and relative configurations were determined by correlation to the
e
f
[
4,6,7]
literature.

2036
Y. Wang, X. Xu, and W. Pei
Scheme 1. The calculated iminium ion model of MM2.
enantioselectivity (>77% yield, >89% ee). This amine-catalyzed Diels–
Alder cycloaddition is also general with respect to diene structure (entries
4
and 5). The acrolein reacted with isoprene and 2,3-dimethylbutdiene to
afford the cycloadduct smoothly (entry 4, 83% yield, 86% ee; entry 5, 89%
yield, 95% ee). It is noteworthy that the reactions depicted in Tables 2
and 3 were performed under an aerobic atmosphere, using wet solvents
and an inexpensive bench-stable catalyst, further illustrating the prepara-
tive advantages of organocatalysis.
Regarding the effects of catalyst 3 on the enantioselectivity of the
Diels–Alder reaction, we propose the calculated iminium ion model of
MM2: the indole group on the catalyst framework effectively shields
[4]
the re face of the dienophile, leaving the si face exposed to cycloaddition.
See Scheme 1.
CONCLUSION
We have shown that catalyst derived from L-tryptophan can be conveni-
ently employed to promote cycloadditions of a,b-unsaturated aldehydes
with dienes. The best reaction medium was CH OH=H O. This amine-
3
2
catalyzed Diels–Alder cycloaddition is also general with respect to the
structure of dienophile and diene.
EXPERIMENTAL
General Information
All solvents were used as obtained from commercial suppliers unless
otherwise indicated. Other commercial reagents were purified prior to
[
8]
use following the guidelines of Huang et al. Reactions were monitored

New Chiral Imidazolidinone
2037
by thin-layer chromatography (TLC). Organic solutions were concen-
trated under reduced pressure on a Yarong evaporator.
1
13
H and C NMR spectra were recorded on a bruker 400 instrument
1
as noted. Data for H NMR are reported as follows: chemical shift (d
ppm), multiplicity (s ¼ singlet, d ¼ doublet, t ¼ triplet, q ¼ quartet,
m ¼ multiplet), integration, coupling constant (Hz), and assignment.
1
3
Data for C NMR are reported in terms of chemical shift. Infrared
(
IR) spectra were recorded on a Bruker spectrometer and are reported
ꢀ1
in terms of frequency of absorption (cm ). Gas liquid chromatography
GLC) was performed on an Agilent 6850 series gas chromatograph using
(
RTX-13100 and AS-H columns (30 m ꢁ 0.25 mm). Progress of the Diels–
Alder reaction was typically monitored by TLC analysis. Absolute
configurations were determined by correlation to the literature.
[
4,6,7]
(5S)-5-((1H-Indol-3-yl)methyl)-2,2,3-trimethylimidazolidin-4-one
hydrochloride (Catalyst 3)
(S)-Tryptophan methyl ester hydrochloride (10 g, 39.3 mmol) was added
to a solution of ethanolic MeNH (16.3 g, 157 mmol), and the resulting
2
solution was stirred at room temperature until the amino ester was
judged to be consumed as determined by TLC (24 h). After removal of
the organic solvents in vacuo, the residue was suspended in Et O and
2
then concentrated. This Et O addition–removal cycle was repeated sev-
2
eral times (to remove excess CH NH ) until (S)-tryptophan N-methyl
3
2
amide hydrochloride was obtained as a white solid. This amide hydro-
chloride was treated with sat. aq. NaHCO (100 ml), and the free amine
3
was extracted with CHCl (10 mL ꢁ 3), dried with Na SO , filtered, and
3
2
4
concentrated. MeOH (200 ml), acetone (50 ml), and p-TSA (0.2 g) were
added to this residue, and the resulting solution was heated to reflux
for 10 h, cooled to room temperature, and then concentrated in vacuo.
The residue was taken up in Et O, and a solution of dioxane–HCl
2
(
4.0 M) was added to precipitate 3. The precipitate was recrystallized
from isopropanol to provide (5S)-5-((1H-indol-3-yl)methyl)-2,2,3-tri-
methylimidazolidin-4-one hydrochloride 3 as colorless crystals in 60%
overall yield from (S)-tryptophan methyl ester hydrochloride (6.9 g,
ꢀ
1
1
2
3.6 mmol). IR (KBr) cm : 3397, 2975, 1674, 1434, 1405; H NMR
(
400 MHz, d -DMSO): 9.00 (s, 1H, NH), 7.57–7.59 (d, J ¼ 7.6 Hz, 1H,
6
ArH), 7.28 (d, J ¼ 0.8 Hz, 1H, ArH), 7.08–7.12 (t, J ¼ 6.4, 8.4 Hz,
1
1
H, ArH), 7.02–7.05 (t, J ¼ 7.2 Hz, 1H, ArH), 6.97–6.99 (d, J ¼ 2.4 Hz,
H, ArH), 3.79–3.82 (t, J ¼ 5.2 Hz, 1H, CH CHCO), 3.24–3.29 (dd,
2
J ¼ 15.0, 4.4 Hz, 1H, CHHCH), 3.14–3.19 (dd, J ¼ 15.2, 6.0 Hz, 1H,
CHHCH), 2.65 (s, 3H, CH ), 2.13 (s, 1H, NH), 1.19 (s, 3H, CH ), 0.98
3
3

2038
Y. Wang, X. Xu, and W. Pei
1
s, 3H, CH3); C NMR (75 MHz, CDCl ) 174.0, 136.1, 127.7, 123.4,
3
(
3
1
21.7, 119.2, 118.5, 111.1, 109.8, 75.4, 58.8, 26.7, 26.2, 25.1, 24.9;
ꢂ
[a]D ¼ ꢀ87.8 (c ¼ 0.01, CHCl ).
3
General Procedure
a,b-Unsaturated aldhyde was added to a solution of (5S)-5-((1H-indol-3-
yl)methyl)-2,2,3-trimethyl-imidazolidin-4-one hydrochloride 3 in CH OH=
3
H O (95=5 v=v). The solution was stirred for 1–2 min before addition of
2
the appropriate diene. Upon consumption of the limiting reagent, the
reaction mixture was diluted with Et O and washed successively with
2
H O and brine. The organic layer was dried with Na SO , filtered, and
2
2
4
concentrated. Hydrolysis of the product dimethyl acetal was performed
by stirring the crude product mixture in TFA–H O–CHCl (1:1:2) for
2
3
2 h at room temperature, followed by neutralization with sat. aq.
NaHCO3 and extraction with Et O. Purification of the Diels–Alder
adduct was accomplished by silica-gel chromatography.
2
Endo-(1S,4R,5S,6S)-6-phenylbicyclo[2.2.1]hex-2-ene-5-carboxaldehyde
and Exo-(1R,4S,5S,6S)-6-phenylbicyclo[2.2.1]hex-2-ene-5-carboxaldehyde
(Table 1, Entry 3)
The title compound was prepared according to the general procedure
with (E)-cinnamaldehyde (0.33 ml, 2.5 mmol), cyclopentadiene (0.75 ml,
7.5 mmol), and 3 (36.69 mg, 0.125 mmol) as a colorless oil in 99% yield
after silica-gel chromatography (EtOAc=hex); 1:1 endo=exo, exo 93%
ee, and endo 90% ee. Product ratios were determined by gas liquid
chromatography (GLC) analysis. Endo isomers t ¼ 30.2, 30.8 min; exo
r
1
isomers t ¼ 28.4, 29.3 min. H NMR (400 MHz, CDCl ) d 9.92 (1H, d,
r
3
J ¼ 2.0 Hz, CHO), 7.13–7.32 (5H, m, Ar-H), 6.33 (1H, dd, J ¼ 3.2,
5
.6 Hz, CH¼CH), 6.07 (1H, dd, J ¼ 3.2, 5.6 Hz, CH¼CH), 3.72 (1H,
dd, J ¼ 3.6, 5.2 Hz, CHPh), 3.23 (1H, br s, CHCH¼CH), 3.22 (1H, br s,
CHCH¼CH), 2.60 (1H, m, CHCHO), 1.56–1.63 (2H, m, CH ). The
2
[
4,6]
absolute configuration was established according to the literature.
Endo-(1S,4R,5R,6S)-6-methylbicyclo[2.2.1]hex-2-ene-5-carboxaldehyde
and Exo-(1R,4S,5R,6S)-6-methylbicyclo[2.2.1]hex-2-ene-5-
carboxaldehyde
The title compound was prepared according to the general procedure
with (E)-crotonaldehyde (0.12 ml, 2.5 mmol), cyclopentadiene (0.75 ml,

New Chiral Imidazolidinone
2039
7
.5 mmol), and 3 (36.69 mg, 0.125 mmol) as a colorless oil in 77%
yield after silica-gel chromatography (EtOAc=hex); 1:1.3 endo=exo, exo
1% ee, endo 91% ee. Product ratios were determined by GLC analy-
sis. Endo isomers t ¼ 28.9, 29.5 min; exo isomers t ¼ 27.0, 27.9 min.
9
r
r
1
H NMR (400 MHz, CDCl ) d 9.78–9.79 (d, J ¼ 2.8 Hz, 1H, CHO),
3
6
3
1
.23–6.25 (dd, J ¼ 5.7, 3.1 Hz, 1H, CH¼CH), 6.15–6.17 (dd, J ¼ 5.7,
.0 Hz, 1H, CH¼CH), 3.02 (br, s, 1H, CHCH¼CH), 2.79 (br, s,
H, CHCH¼CH), 2.37–2.45 (m, 1H, CHCHO), 1.70–1.73 (m, 1H,
CHCH ), 1.44–1.48 (m, 2H, CH ), 0.89–0.91 (d, J ¼ 6.9 Hz, 3H,
3
2
CHCH ). The absolute configuration was established according to the
3
[
4,6]
literature.
Endo-(1S,4R,5S,6S)-6-furan-2-ylbicyclo[2.2.1]hex-2-ene-5-carboxalde-
hyde and Exo-(1R,4S,5S,6S)-6-furan-2-ylbicyclo[2.2.1]hex-2-ene-5-
carboxaldehyde (Table 3, Entry 3)
The title compound was prepared according to the general procedure
with (E)-3-furanyl-acrolein (305 mg, 2.5 mmol), cyclopentadiene
(
9
0.75 ml, 7.5 mmol), and 3 (36.69 mg, 0.125 mmol) as a colorless oil in
0% yield after silica-gel chromatography (EtOAc=hex); 1.1:1 endo=exo,
exo 89% ee; endo 84% ee. Product ratios were determined by GLC
analysis. Endo isomers t ¼ 26.0, 26.7 min; exo isomers t ¼ 23.9,
r
r
1
2
7
6
4.9 min. H NMR (400 MHz, CDCl ) d 9.56 (d, J ¼ 1.9 Hz, 1H, CHO),
3
.32 (d, J ¼ 1.0 Hz, 1H, furyl), 6.35 (dd, J ¼ 5.6, 3.1 Hz, 1H, CH¼CH),
.30 (dd, J ¼ 3.1, 1.9 Hz, 1H, furyl), 6.13 (dd, J ¼ 5.6, 2.7 Hz, 1H,
CH¼CH), 6.07 (d, J ¼ 3.2 Hz, 1H, furyl), 3.33 (br, s, 1H), 3.13–3.09
(
m, 1H), 3.18–3.04 (m, 2H), 1.78 (br, d, J ¼ 8.7 Hz, 1H), 1.59–1.53
(m, 2H). The absolute configuration was established according to the
literature.
[
4,6]
(
R)-4-Methylcyclohex-3-enecarbaldehyde (Table 3, Entry 4)
The title compound was prepared according to the general procedure
with acrolein (0.2 ml, 3.0 mmol), isoprene (1.5 ml, 15 mmol), and 3
(
44.0 mg, 0.15 mmol) as a colorless oil in 83% yield after silica-gel
chromatography (EtOAc=hex). Product ratios were determined by
GLC analysis. S isomers t ¼ 4.9 min; R isomers t ¼ 5.3 min; R 86% ee.
r
r
1
H NMR (400 MHz, CDCl ) d 9.70 (s, 1H, CHO), 5.41 (br, 1H, CH¼C),
3
2
.44 (m, 1H, CH), 2.21 (br, 2H, CH ), 2.00 (br, 2H, CH ), 1.97 (m,
2 2
1
uration was established according to the literature.
H, CHH), 1.69 (m, 1H, CHH), 1.65 (s, 3H, CH ). The absolute config-
3
[
4]

2040
Y. Wang, X. Xu, and W. Pei
(R)-3,4-Dimethylcyclohex-3-enecarbaldehyde (Table 3, Entry 5)
The title compound was prepared according to the general procedure
with acrolein (0.2 ml, 3.0 mmol), 2,3-dimethylbutdiene (1.5 ml, 12.5mmol),
and 3 (44.0 mg, 0.15mmol) as a colorless oil in 89% yield after silica-gel
chromatography (EtOAc=hex). Product ratios were determined by GLC
1
analysis. S isomers t ¼ 4.9 min; R isomers t ¼ 5.4 min; R 95% ee. H
r
r
NMR (400MHz, CDCl ) d 1.61 (s, 3H, CH ), 1.65 (s, 3H, CH ), 1.90–
3
3
3
2
.06 (m, 4H, CH ), 2.09–2.19 (m, 2H, CH ), 2.42–2.58 (m, 1H, CH),
2 2
9.69 (s, 1H, CHO). The absolute configuration was determined according
to the literature.
[4]
ACKNOWLEDGMENTS
We are indebted to Xu Xu and Shuping Luo for performing the GLC
analyses. We are also grateful to the Key Subject of Industrial Catalysis
for financial support.
REFERENCES
1
. For reviews on enantioselective Diels–Alder reactions, see (a) Oppolzer, W.
Asymmetric Diels–Alder and ene reactions in organic synthesis: New synthetic
methods. Angew. Chem., Int. Ed. Engl. 1984, 23, 876–889; (b) Kagan, H.;
Riant, O. Catalytic asymmetric Diels–Alder reactions. Chem. Rev. 1992, 92,
1007–1019; (c) Corey, E. J. Catalytic enantioselective Diels–Alder reactions:
Methods, mechanistic fundamentals, pathways, and applications. Angew.
Chem., Int. Ed. Engl. 2002, 41, 1650–1667.
2
. (a) Wada, E.; Pei, W.; Kanemasa, S. Exclusively endo-selective Lewis acid–
catalyzed hetero Diels–Alder reactions. Chem. Lett. 1994, 2345–2350; (b)
Pei, W. Chem. J. Chin. Univ. 1998, 19, 399–401.
3
. (a) Dalko, P. I.; Moisan, L. In the golden age of organocatalysis. Angew.
Chem., Int. Ed. Engl. 2004, 43, 5138–5175; (b) List, B. Organocatalysis: A com-
plementary catalysis strategy advances organic synthesis. Adv. Synth. Catal.
2004, 346, 1021; (c) Houk, K. N.; List, B. Asymmetric organocatalysis. Acc.
Chem. Res. 2004, 37, 487; (d) Notz, W.; Tanaka, F.; Barbas, C. F. III.
Enamine-based organocatalysis with proline and diamines: The development
of direct catalytic asymmetric aldol, Mannich, Michael, and Diels–Alder reac-
tions. Acc. Chem. Res. 2004, 37, 580–591; (e) Dalko, P. I.; Moisan, L. Enan-
tioselective organocatalysis. Angew. Chem., Int. Ed. Engl. 2001, 40, 3726–
3748; (f) France, S.; Guerin, D. J.; Miller, S. J.; Lectka, T. Nucleophilic chiral
amines as catalysts in asymmetric synthesis. Chem. Rev. 2003, 103, 2985–3012.
. Ahrendt, K. A.; Borths, C. J.; MacMillan, D. W. C. New strategies for organic
catalysis: The first highly enantioselective organocatalytic Diels–Alder
reaction. J. Am. Chem .Soc. 2000, 122, 4243–4244.
4

New Chiral Imidazolidinone
2041
5
. (a) Corey, E. J. Catalytic enantioselective Diels–Alder reactions: methods,
mechanistic fundamentals, pathways, and applications. Angew. Chem., Int.
Ed. Engl. 2002, 41, 1650; (b) Corey, E. J.; Loh, T.-P. First application of
attractive intramolecular interactions to the design of chiral catalysts for
highly enantioselective Diels–Alder reactions. J. Am. Chem. Soc. 1991, 113,
8
966–8967.
6
. Mosse, S.; Alexakis, A. Organocatalyzed asymmetric reactions via microwave
activation. Org. Lett. 2006, 8, 3577–3580.
7
. Ishihara, K.; Kurihara, H.; Matsumoto, M.; Yamamoto, H. Design of
Brønsted acid–assisted chiral Lewis acid (BLA) catalysts for highly enantiose-
lective Diels–Alder reactions. J. Am. Chem. Soc. 1998, 120, 6920–6930.
. Huang, Q.; Xie, R. G.; Tian, B. Z.; Qing, S. Y. Synthetic Handbook of Organic
Reagents, 2nd ed.; Chemical Industry Press: Beijing, 2005.
8