Carbohydrate-based tolylsulfonyl hydrazines: Effective catalysts for the Mannich reaction and the syntheses of bisindolylalkanes in water

Article abstract of DOI:10.1071/CH08004

Three carbohydrate-based tolylsulfonyl hydrazines were used to catalyze the three-component Mannich reaction, as well as the adduct reaction of aldehyde and indole to prepare bisindolylalkanes in water. Moderate to good yields were achieved. The results demonstrate that carbohydrate derivatives can be employed as effective catalysts in water, and an environmentally benign methodology was developed to synthesize bioactive bisindolylalkanes and the β-amino carbonyl framework. CSIRO 2008.

Full text of DOI:10.1071/CH08004

Full Paper
CSIRO PUBLISHING
www.publish.csiro.au/journals/ajc
Aust. J. Chem. 2008, 61, 359–363
Carbohydrate-Based Tolylsulfonyl Hydrazines: Effective
Catalysts for the Mannich Reaction and the Syntheses
of Bisindolylalkanes in Water
Peng Wu,A,B Yiqian Wan, and Jiwen Cai
B
A,B,C
A
School of Pharmaceutical Sciences, Sun Yat-Sen University, Guangzhou 510080, China.
School of Chemistry and Chemical Engineering, Sun Yat-Sen University,
Guangzhou 510275, China.
B
C
Corresponding author. Email: puscjw@mail.sysu.edu.cn
Three carbohydrate-based tolylsulfonyl hydrazines were used to catalyze the three-component Mannich reaction, as well
as the adduct reaction of aldehyde and indole to prepare bisindolylalkanes in water. Moderate to good yields were
achieved. The results demonstrate that carbohydrate derivatives can be employed as effective catalysts in water, and an
environmentally benign methodology was developed to synthesize bioactive bisindolylalkanes and the β-amino carbonyl
framework.
Manuscript received: 6 January 2008.
Final version: 8 April 2008.
OH
Introduction
O
O
S
Performing organic reactions in aqueous media is of current
interest, because water is cheap, safe, and environmentally
benign. However, using water as the sole medium for organic
reactions is not always practical because of the poor solubil-
HO
HO
Catalyst 1:
Catalyst 2:
NH NH
Tol
[
1]
OH
OH
O
HO
O
O
ity of organic molecules in water, as well as the possibility that
water could inhibit the catalyst’s activity.[1] Consequently, cata-
HO
NH NH
S
Tol
Tol
OH
O
lysts suitable for activation of organic reactions in water require
special design.
O
O
HO
HO
Catalyst 3:
Amine-based organocatalysis is an effective platform for car-
rying out organic transformations, and many powerful aminocat-
NH
S
NH
OH
O
[2]
alysts have been developed in recent years. Although a few
aminocatalysts can be used in water,[ most of the reactions
were typically performed in organic solvents. Recently, sev-
eral surfactant-type organic amines have been successfully used
to catalyze organic reactions in water.[ Moreover, Tomkinson
reported that hydrazides could catalyze Diels–Alder reactions
and trigger the formation of bisindolylalkanes efficiently.[
This made us wonder whether the carbohydrate-based hydrazide
derivatives could be used as aminocatalysts to activate organic
reactions in water. A series of carbohydrate-based tolylsulfonyl
hydrazines that carry both the hydrophilic and hydrophobic
groups, as shown in Fig. 1, were selected as the surfactant-type
catalysts to increase the solubility of both the substrate and the
catalyst, and their catalytic efficiency for the adduct reaction
between aldehyde and indole, as well as the three-component
Mannich reactions in water, was investigated.
3]
Fig. 1. Carbohydrate-based tolylsulfonyl hydrazines.
O
S
O
S
4]
Glycose
NHNH2
NHNH gly
CH CH OH
5]
O
3
2
O
Catalyst 1: gly ϭ D-glucopyranosyl
Catalyst 2: gly ϭ D-galacopyranosyl
Catalyst 3: gly ϭ D-xylopyranosyl
Scheme 1. The synthesis protocol for the catalysts.
Direct Three-Component Mannich Reactions
The Mannich reaction has been a very effective platform to
produce β-amino carbonyl compounds, including various phar-
maceutical and natural products, as well as their synthetic
intermediates. The classical Mannich reaction has serious dis-
advantages and substrate limitation. The modern versions of
Mannich reactions have extended the substrate scope by using
Results and Discussion
Our approach began with the preparation of catalysts 1–3 from
glycoses according to the literature, as shown in Scheme 1.[
These carbohydrate derivatives were then examined for their
ability to activate the C–C bond formation reactions in water.
6]
[7]
©
CSIRO 2008
10.1071/CH08004
0004-9425/08/050359

3
60
P. Wu, Y. Wan, and J. Cai
silyl enolates instead of ketones as nucleophilic components.[8]
However, employing silyl enolates, which are prepared under
anhydrous conditions, was not an atom-economic and environ-
mentally benign approach. Protocols that employ unmodified
carbonyl donor, amine, and aldehyde as reaction substrates and
use water as the sole reaction medium are of great interest. So far,
only a few one-pot three-component Mannich reactions carried
out in water have been reported.[ Herein, we present the direct
three-component Mannich-type reactions catalyzed by a series
of carbohydrate-based tolylsulfonyl hydrazines for the first time.
Initially, we chose the condensation reaction of benzalde-
hyde, aniline, and acetophenone in aqueous media as the model
reaction, and the catalytic efficiency of the three glycosyl deriva-
tives in aqueous media was evaluated.As summarized inTable 1,
moderate yields were achieved for all three catalysts, with the
glucose derivative (catalyst 1) being the most efficient one
(Table 1, entry 1). When organic solvents such as chloroform,
acetonitrile, toluene, or DMSO were employed, the reactions
were feasible and the desired products were obtained in low
yield with the formation of side products (Table 1, entries 4–7).
Addition of the surfactant sodium dodecyl sulfate (SDS) did not
improve the catalytic efficiency (Table 1, entry 9). When SDS
was used alone, only 5% of the desired product was obtained
(Table 1, entry 8).
9]
Based on the results obtained above, the generality of the
procedure was investigated and the results are summarized in
Table 2. The condensation of various aldehydes, amines, and
ketones was found to be catalyzed efficiently by catalyst 1
at room temperature in water. The catalyst was effective for
aldehydes including aromatic aldehydes (Table 2, entries 1–9),
heteroaromatic aldehydes (Table 2, entry 12), and aliphatic alde-
hydes (Table 2, entries 10 and 11). For an enolizable aliphatic
aldehyde (isovaleraldehyde), which is not always suitable for the
conventional Mannich reaction, the target product could also be
attained in 61 and 69% yields (Table 2, entries 10 and 11). More-
over, benzaldehyde, p-anisidine, and acetophenone produced the
Mannich adduct in 59% yield in our protocol (Table 2, entry 2),
in contrast to the conventional HCl-catalyzed reaction in EtOH
with only 30% transformation.[ Finally, when active reaction
substrates were employed, the catalytic loading could be lowered
to 10 mol-% (Table 2, entries 3 and 7). It was noteworthy that
the catalyst could be recycled, and 65% yield was attained for
the addition of benzaldehyde, aniline, and cyclohexanone in the
second round.
Table 1. The catalytic efficiency of carbohydrate-based tolylsulfonyl
hydrazines on the three-component Mannich reaction in various media
All reactions were performed at room temperature. Yields are of isolated
1
13
products. All products were characterized by H NMR, C NMR, IR,
and MS
Ph
O
NH
O
Catalyst (20mol-%)
H2O, r.t.
PhCHO ϩ PhNH2
ϩ
Ph
(2.0eq)
Ph
Ph
(
1.0eq)
(1.1eq)
10]
Entry
Catalyst
Solvent
Yield [%]/
time [h]
1
2
3
4
5
6
7
8
9
Catalyst 1
Catalyst 2
Catalyst 3
Catalyst 1
Catalyst 1
Catalyst 1
Catalyst 1
Sodium dodecyl sulfate
Catalyst 1 + sodium
dodecyl sulfate
H2O
H2O
H2O
Chloroform
Ccetonitrile
Toluene
DMSO
65/16
60/16
62/16
12/24
16/24
10/24
48/24
5/24
Syntheses of Bisindolylalkanes
Bisindolylalkanes and their derivatives are widely found in
[11]
bioactive metabolites of terrestrial and marine origin.
Con-
H2O
H2O
siderable attention has been paid to the synthetic methods
leading to indole derivatives. It has been reported that bisindolyl-
67/16
alkanes could be prepared using either protic[ or Lewis
12]
[13]
Table 2. The catalytic efficiency of catalyst 1 on the three-component direct Mannich reactions
1
13
Yields are of isolated products. All products were characterized by H NMR, C NMR, IR, and MS
R2
O
NH
O
Catalyst 1
1
2
R4
R1
R4
R CHO ϩ R NH
ϩ
2
H O, r.t.
2
R3
R3
Entry
R1
R2
R3
R4
Catalyst 1 [mol-%]
Anti/synA
Yield [%]/
reaction time [h]
1
2
3
4
5
6
7
8
9
Ph
Ph
Ph
Ph
H
H
Ph
Ph
20
20
10
20
20
20
10
20
20
20
20
20
–
–
65/16
59/21
85/12
80/12
76/14
82/14
95/12
91/12
87/14
61/12
69/14
62/12
4-CH3OC6H4
Ph
Ph
Ph
–(CH2)4–
–(CH2)4–
–(CH2)4–
–(CH2)4–
–(CH2)4–
–(CH2)4–
–(CH2)4–
–(CH2)4–
–(CH2)4–
–(CH2)4–
78/22
69/31
58/42
71/29
50/50
52/48
64/36
70/30
69/31
57/43
4-ClC6H4
4-BrC6H4
4-NO2C6H4
Ph
4-ClC6H4
4-NO2C6H4
(CH3)2CHCH2
(CH3)2CHCH2
2-furfural
Ph
4-ClC6H4
4-ClC6H4
4-ClC6H4
Ph
4-ClC6H4
Ph
1
1
1
0
1
2
A
1
1
Diastereomeric ratio determined by H NMR spectroscopy, the syn/anti isomers were determined from H NMR coupling constants.

Carbohydrate-Based Tolylsulfonyl Hydrazines
361
acids as the catalysts to treat aldehydes with a two-fold excess
of indole. However, these reactions generally require strongly
acidic reaction conditions and elevated temperature to achieve
reasonable yield or it has to endure the high cost of the catalyst.
With the increasing interests in environmentally friendly reac-
bisindolylalkanes in water, as shown in Scheme 2. Vibrindole
[17]
A,
a bacterial metabolite, was first targeted and attained in
70% yield from the reaction of indole and acetaldehyde solu-
tion in water. Trisindolylalkane, isolated from the bacterium
Vibrio parahaemolyticus,[ was produced from the coupling
of indole-3-carboxaldehyde and indole in 50% yield.
18]
[14]
tions, novel methodologies including solvent-free reactions,
[
5a]
[15]
organocatalysis,
ionic liquids
and SDS catalysis,
as well as the use of
With regard to the catalytic mechanism, we believe that the
formation of the iminium ion was the key step in the reaction,
as in that described by Tomkinson for a similar reaction carried
out in organic solvent.[ The tolylsulfonyl hydrazine group was
the effective catalytic component, and the carbohydrate group
functioned as a surfactant component to promote better interac-
tion between the organic substrates and the catalyst in aqueous
media.
[
16]
have been developed to synthesize bisindoly-
lalkanes. Herein, we test the abilities of the carbohydrate-based
tolylsulfonyl hydrazines for the preparation of bisindolylalkanes
in aqueous medium.
5]
Catalyst 1 was initially employed, and the reaction between
propionaldehyde and indole to produce bisindolylalkane was
used as the model reaction. As summarized in Table 3, in less
polar solvents such as chloroform and acetonitrile, the reaction
could not proceed (Table 3, entries 1 and 2). When more polar
solvents such as DMF and DMSO were employed (Table 3,
entries 3 and 4), the reaction was feasible, with 26 and 30%
transformation in 24 h. A remarkable change occurred when the
reactions were carried out in protic solvents, such as methanol
and water, with the desired bisindolylalkane isolated in 60 and
Among various indole derivatives, diindol-3-ylmethane has
been gaining increasing importance in recent years because
of its potent anticarcinogenic properties.[ We were able to
19]
Table 4. Scope of bisindolylalkane formation
All reactions were performed at room temperature. Yields are of isolated
products. All products were characterized by 1H NMR, 13C NMR, IR,
6
5% yield, respectively (Table 3, entries 5 and 6). Similar solvent
and MS
R
effects were reported for the synthesis of bisindolylalkane cat-
alyzed by benzoic hydrazide-derived catalyst.[ In the absence
of the catalyst, the desired product was not detected (Table 3,
entry 7). The xylose-based catalyst 3 was found to be the most
efficient one in water (Table 3, entries 8 and 9).
5b]
Catalyst 3
R
CHO ϩ
Water, r.t.
N
H
N
H
N
H
The generality of the procedure was investigated and the
results are summarized in Table 4. The reaction was effective
for a variety of aldehydes including aliphatic (Table 4, entries
Entry
R
Catalyst [mol-%]
Yield [%]/
reaction time [h]
1
–3), aromatic (Table 4, entries 4–13), and heteroaromatic alde-
1
2
3
4
5
6
7
8
9
CH3CH2–
20
20
20
10
10
10
10
10
10
10
10
10
10
10
72/12
68/14
70/14
84/12
90/10
80/12
93/12
88/12
80/10
79/10
84/12
75/10
89/10
92/10
hydes (Table 4, entry 14).The catalytic loading could be lowered
to 10 mol-% for catalyst 3, with the bisindolylalkane adduct iso-
lated in good to excellent yield (Table 4, entries 4–14). In the
case of terephthalaldehyde, which bears two –CHO groups, only
one of them reacted with indole and produced bisindolylalkane
in 89% yield (Table 4, entry 13).
CH3CH2CH2–
(CH3)2CHCH2–
C6H5–
p-ClC6H4–
p-BrC H –
6
4
p-NO2C6H4–
m-NO2C6H4–
p-CH3OC6H4–
p-(CH3)2NC6H4–
p-HOC6H4–
p-CH3C6H4–
p-OHCC6H4–
2-furfural
The mild and environmentally benign methodology was
employed to prepare
a variety of naturally occurring
10
11
12
13
14
Table 3. The catalytic efficiency of carbohydrate-based tolylsulfonyl
hydrazines on the reaction of indole and propionaldehyde in different
solvent media
All reactions were performed at room temperature. Yields are of isolated
products. All products were characterized by H NMR, C NMR, IR,
1
13
and MS
Et
O
Catalyst
H
N
ϩ
O
Catalyst 3 (20mol-%)
Solvent, r.t.
N
H
Et
N
H
2
N
H
N
H
N
H
ϩ
Water, r.t.
Vibrindole A 70% yield
H
N
Entry
Catalyst [mol-%]
Solvent
Yield [%]/
reaction time [h]
CHO
H
N Catalyst 3 (20mol-%)
ϩ 2
1
2
3
4
5
6
7
8
9
1 (20)
1 (20)
1 (20)
1 (20)
1 (20)
1 (20)
None
CHCl3
CH3CN
DMF
DMSO
CH3OH
H2O
H2O
H2O
H2O
0
0
N
Water, r.t.
H
N
H
N
H
26/24
30/24
60/24
65/12
0
Trisindolylalkane 50% yield
H
O
N Catalyst 3 (20mol-%)
ϩ
2
H
H
Water, r.t.
N
H
N
H
Diindol-3-ylmethane 75% yield
2 (20)
3 (20)
68/12
72/12
Scheme 2. Synthesis of naturally occurring bisindolylalkanes.

3
62
P. Wu, Y. Wan, and J. Cai
attain diindol-3-ylmethane in 75% yield in water using the
methodology we developed.
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