Noyori's Ts-DPEN ligand: an efficient bifunctional primary amine-based organocatalyst in enantio- and diastereoselective Michael addition of 1,3-dicarbonyl indane compounds to nitroolefins

Article abstract of DOI:10.1016/j.tetlet.2008.09.025

Noyori's Ts-DPEN ligand bearing an amino sulfonamide moiety and with a primary amino group on a chiral scaffold was found to be a simple and efficient bifunctional organocatalyst for the asymmetric Michael addition of 1,3-dicarbonyl compounds to nitroolefins, which gave highly functional Michael adduct with quaternary stereocenters in good enantioselectivities (up to 84%ee) and dr (up to 5.7:1 dr).

Full text of DOI:10.1016/j.tetlet.2008.09.025

Tetrahedron Letters 49 (2008) 6773–6777
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Noyori’s Ts-DPEN ligand: an efficient bifunctional primary amine-based
organocatalyst in enantio- and diastereoselective Michael addition
of 1,3-dicarbonyl indane compounds to nitroolefins
a
a
a
a
c
Ya-Dong Ju a, Li-Wen Xu a,b, , Li Li , Guo-Qiao Lai , Hua-Yu Qiu , Jian-Xiong Jiang , Yixin Lu
*
a Key Laboratory of Organosilicon Chemistry and Material Technology of Ministry of Education, Hangzhou Normal University, Hangzhou 310012, PR China
b State Key Laboratory for Oxo Synthesis and Selective Oxidation, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, PR China
c Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543, Republic of Singapore
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 27 July 2008
Revised 3 September 2008
Accepted 8 September 2008
Available online 11 September 2008
Noyori’s Ts-DPEN ligand bearing an amino sulfonamide moiety and with a primary amino group on a chi-
ral scaffold was found to be a simple and efficient bifunctional organocatalyst for the asymmetric Michael
addition of 1,3-dicarbonyl compounds to nitroolefins, which gave highly functional Michael adduct with
quaternary stereocenters in good enantioselectivities (up to 84%ee) and dr (up to 5.7:1 dr).
Ó 2008 Published by Elsevier Ltd.
Keywords:
Primary amine
Dual activation
Michael addition
Organocatalysis
Chiral bifunctional catalysts have attracted growing attention in
the past decades.1 It is considered that by imitating nature, the
principle of bifunctional catalysis could offer many advantages.2
Catalysts that contain two reaction partners in close proximity
and with the correct relative geometry could activate and facilitate
both reagent and substrate in a controlled environment or, alterna-
tively, one reactive center could be used to bind to the substrate,
whilst the second active site performs the chemical transforma-
tion.3 Such synergistic cooperation or dual activation between
two functionalities would be similar to enzymatic catalysis. Aspir-
ing to imitate enzymatic synergistic cooperation of multicenters,
chemists have succeeded in designing and developing many kinds
of bifunctional and multifunctional catalysts for asymmetric syn-
thesis, such as CBS reduction, aminoalcohol-mediated addition of
dialkylzinc, Shibasaki’s hetero- and homobimetallic catalysts, Jac-
obsen’s metal–salen complexes, and Trost’s chiral semiazacrown
Zn complex.4 Since the pioneering works in 2000,5 impressive pro-
gress has been made recently in the development of bifunctional
organocatalysis for organic synthesis.6 And pyrrolidine- and imi-
dazoline-type catalysts with secondary amines are widely used
organocatalysts in the past years, in which the asymmetric enam-
ine catalysis of ketone or aldehyde has been commonly accepted.7
By comparison, chiral primary amine-based bifunctional organo-
catalysts also received increasing attention.8 Primary amine cata-
lysis is effectively exploited by enzymes such as type I aldolases,
decarboxylases, and dehydratases, each of which contain catalyti-
cally active lysine or threonine residues.9 Considering the particu-
larities and potentials of primary amine-based organocatalysis, we
herein report that Noyori’s Ts-DPEN ligand with an amino sulfon-
amide moiety and a primary amino group on a chiral scaffold is
revealed to be highly efficient for the asymmetric Michael addition
of 1,3-dicarbonyl indane compounds to nitroolefins, which gave
highly functional Michael adduct with quaternary stereocenters
in good enantioselectivities.
Michael reaction of nitroolefins represents a direct and most
appealing approach to chiral nitroalkanes that are versatile inter-
mediates in organic synthesis, which is tied to their propensity
to undergo facile
a-alkylation reaction and interconversions to
other important organic functional groups.10 Although the catalytic
asymmetric versions of this reactions were achieved, most re-
quired metal catalyst or strict reactions conditions,11 and the chiral
construction of a quaternary carbon atom via Michael addition is
rare.12 Recently, the utility of urea (thiourea)-based organocata-
lysts has been proved to be effective in the Michael addition of
ketones to nitroolefins, which is due to their strong activation of
carbonyl and nitro groups through efficient double-hydrogen-
bonding interactions.13 Notably, N-sulfonylcarboxamides, which
contain an acidic hydrogen with a pKa value similar to that of the
carboxyl acid group, also represent a novel fine-tuning class of
* Corresponding author. Tel./fax: +86 0571 28865135.
E-mail addresses: licpxulw@yahoo.com, liwenxu@hznu.edu.cn (L.-W. Xu).
0040-4039/$ - see front matter Ó 2008 Published by Elsevier Ltd.
doi:10.1016/j.tetlet.2008.09.025

6774
Y.-D. Ju et al. / Tetrahedron Letters 49 (2008) 6773–6777
O
2
O
O
OMe
NO2
Organocatalyst
O
+
H
NO2
OMe
1a
2a
3a
N
N
COOH
N
MeO
H
HO
HO
N
H
N
Cat-1: L-Proline
H
Cat-2: Quinine
Cat-3: Cinchonidine
O
H2N HN S
O
H2N
NH2
Cat-4: DPEN
Cat-5: Ts-DPEN
Scheme 1.
Table 1
Michael reaction of nitrostyrene with various catalysts under different conditions
highly enantioselective organocatalysts for aldol and Michael addi-
tion;14 however, simple amino N-sulfonamides with weak single-
hydrogen-bonding interaction received little attractions. Up to
date, there are only a few literatures that reported the simple
organocatalyst bearing amino N-sulfonamides-catalyzed organic
transformations.15 Inspired by the proven ability of thiourea and
N-sulfonylamides with hydrogen-bonding functionality in the
asymmetric addition reactions, we envisioned that an appropriate
combination of N-sulfonamide and primary amine in a chiral scaf-
fold could result in a potential bifunctional organocatalyst. Herein,
we described the asymmetric organocatalytic Michael addition
containing tertiary stereocenters, which is promoted by a simple
bifunctional organocatalyst bearing an amino sulfonamide moiety
and with a primary amino group on a chiral scaffold.
Entrya
Cat.
Solvent
T (°C)
Yieldb (%)
dr (2R/2S)c
ee % (major)d
1
2
3
4
5
6
7
8
9
10
11
12
13e
Cat-1
Cat-2
Cat-3
Cat-4
Cat-5
Cat-5
Cat-5
Cat-5
Cat-5
Cat-5
Cat-5
Cat-5
Cat-5
Toluene
Toluene
Toluene
Toluene
Toluene
MeOH
THF
CH3CN
DCM
Toluene
Toluene
Toluene
Toluene
À20
À20
À20
À20
À20
À20
À20
À20
À20
20
40
67
81
80
87
93
66
60
51
81
90
50
86
1.2:1
1.0:1
1.4:1
1.9:1
4.0:1
1.2:1
2.3:1
1.5:1
2.8:1
4.0:1
4.0:1
2.3:1
4.6:1
2
20
3
11
73
4
26
11
42
65
66
59
70
0
À78
À20
There are few reports of Michael reaction of ketoesters to nitro-
olefins constructing a stereogenic quaternary carbon center with
high diastereo- and enantioselectivity.12 Therefore the Michael
a
Note: The reaction was performed with 1.0 mmol of nitrostyrene, 1.1 mmol of
cyclic b-ketoester (2a), 10 mol % of catalyst, for 24 h.
b
GC yield.
c
Determined by 1H NMR.
reaction of nitrostyrene (1a) and
a-substituted cyclic b-ketoester
d
The ee values of major products were determined by HPLC (see Supplementary
(methyl 1-oxo-2,3-dihydro-1H-indene-2-carboxylate, 2a) was se-
lected as model reactions (Scheme 1). Initially, different commer-
cially available organocatalysts were examined, and the results
data).
e
5 mol % of Ts-DPEN.
are summarized in Table 1. L-Proline and other chiral Lewis base,
including primary diamine, (R,R)-1,2-diphenylethylenediamine
(DPEN), showed low enantioselectivities and dr (Table 1, entries
1–4). We then synthesized a simple organocatalyst, Ts-DPEN, bear-
ing an amino sulfonamide moiety from (R,R)-1,2-diphenylethyl-
enediamine (DPEN), which could activate the nitrostyrene with
hydrogen-bonding interactions. It is known that the Ts-DPEN and
(Table 1, entries 5–9). Further optimization of standard parameters
revealed that the reaction carried out at À20 °C in the presence of
5% to 10 mol % of the catalytic Ts-DPEN represents the best reactiv-
ity and enantioselectivity (Table 1, entries 10–13).
We next examined the scope of this class of Michael reactions
with a series of nitroolefins and cyclic b-ketoesters under the opti-
mized reaction conditions. Table 2 summarizes the results using
different substrates. The Michael reaction of different substituted
nitroolefins with methyl 1-oxo-2,3-dihydro-1H-indene-2-carbox-
ylate (2a) proceeded smoothly with good enantioselectivities
(Table 2, entries 1–9, 67–84% ee). In this way, it was revealed that
all the Michael adducts with various nitroolefins were obtained in
good yields and enantioselectivities. Furthermore, the Michael
reaction of various cyclic b-ketoesters and nitroolefins gave
corresponding adducts with good enantioselectivities and yields
(entries 10–15, up to 71% ee, up to 5.3 dr). The scope of the reaction
Noyori’s Ts-DPEN ligand, in combination with Ru(II)Cl(6
g-arene),
exhibited high enantiofacial discrimination ability in hydrogena-
tion.16 However, to the best of our knowledge, no report is known
of Ts-DPEN-catalyzed organic reaction. Herein, to our surprise, as
shown in Table 1 (entry 5), the Noyori’s Ts-DPEN ligand showed
the best enantioselectivities (73% ee and 4:1 dr) compared to pre-
vious organocatalyst (cat-1 to cat-4). These results indicated that
N-sulfonamide is crucial for a high yield and selectivity. We then
carried out Michael reaction of nitrostyrene (1a) and cyclic b-keto-
ester (2a) in different solvent. Evaluation of usual reaction media
led to the further identification of toluene as the best solvent

Y.-D. Ju et al. / Tetrahedron Letters 49 (2008) 6773–6777
6775
Table 2
Enantio- and diastereoselective Michael reactions of nitroolefins in the presence of catalytic Ts-DPEN
O
O
OMe
NO2
2
R2
O
3
R1
Ts-DPEN(10mol%)
n
O
H
R2
toluene
+
NO2
R1
OMe
-20 °C
n
1
3
2
Entrya
1
Nitroolefins
Cyclic b-ketoesters
Time (h)
Yieldb (%)
dr (2R/2S)c
eed (%)
68
O
O
NO2
24
24
24
24
24
24
85
3.2:1
OMe
O
O
O
O
O
NO2
O
2
3
4
5
6
81
72
78
81
79
5.7:1
4.6:1
3.0:1
4.9:1
4.6:1
80
73
71
71
69
Cl
OMe
NO2
O
Br
OMe
NO2
O
MeO
Cl
OMe
NO2
NO2
O
OMe
O
Cl
Cl
OMe
O
O
O
NO2
O
7
8
24
24
24
48
48
48
85
77
76
72
87
78
4.9:1
3.3:1
5.7:1
2.7:1
4.8:1
3.0:1
77
84
67
71
73
68
F
OMe
NO2
O
Br
NC
Br
Br
Br
OMe
NO2
O
9
OMe
O
NO2
NO2
NO2
O
10
11
12
OMe
O
MeO
O
OMe
O
O
(continued on next page)
OMe
Br

6776
Y.-D. Ju et al. / Tetrahedron Letters 49 (2008) 6773–6777
Table 2 (continued)
Entrya
Nitroolefins
Cyclic b-ketoesters
Time (h)
48
Yieldb (%)
83
dr (2R/2S)c
eed (%)
60
O
NO2
NO2
O
13
14
3.2:1
Cl
OMe
O
MeO
O
48
48
85
87
5.3:1
2.8:1
70
64
Cl
OMe
O
NO2
O
15
Cl
OMe
Br
a
The reaction was performed with 1.0 mmol of nitrostyrene, 1.1 mmol of cyclic b-ketoester 2a), 10 mol % of Ts-DPEN, in toluene (2 mL), at À20 °C.
b
c
Isolated yield.
Determined by 1H NMR.
d
The ee values of major prodcuts were determined by HPLC (see Supplementary data), and the relative configuration was determined by comparing the retention time of
HPLC of products with that of the literature data.12e
and Dr. Kanai, Graduate School of Pharmaceutical Sciences, The
University of Tokyo, for their help.
Supplementary data
O
H
H
S
N
O
O
R
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.tetlet.2008.09.025.
O
N
N
H
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O
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O
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Acknowledgments
This work was supported in part by Hangzhou Normal Univer-
sity and the National Nature Science Foundation of China (Project
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