From waste biomass to solid support: Lignosulfonate as a cost- Effective and renewable supporting material for catalysis

Article abstract of DOI:10.1002/chem.201303364

Lignosulfonate (LS) is an organic waste generated as a byproduct of the cooking process in sulfite pulping in the manufacture of paper. In this paper, LS was used as an anionic supporting material for immobilizing cationic species, which can then be used as heterogeneous catalysts in some organic transformations. With this strategy, three lignin-supported catalysts were prepared including 1) lignin- SO₃Sc(OTf)₂, 2) lignin-SO₃Cu(OTf), and 3) lignin-IL@NH₂ (IL= ionic liquid). These solid materials were then examined in many organic transformations. It was finally found that, compared with its homogeneous counterpart as well as some other solid catalysts that are prepared by using different supports with the same metal or catalytically active species, the lignin-supported catalysts showed better performance in these reactions not only in terms of activity but also with regard to recyclability.

Full text of DOI:10.1002/chem.201303364

DOI: 10.1002/chem.201303364
Full Paper
&
Green Chemistry
From Waste Biomass to Solid Support: Lignosulfonate as a Cost-
Effective and Renewable Supporting Material for Catalysis
Shaohuan Sun,[a] Rongxian Bai,*[a] and Yanlong Gu*[a, b]
Abstract: Lignosulfonate (LS) is an organic waste generated
as a byproduct of the cooking process in sulfite pulping in
the manufacture of paper. In this paper, LS was used as an
anionic supporting material for immobilizing cationic spe-
cies, which can then be used as heterogeneous catalysts in
some organic transformations. With this strategy, three
lignin-supported catalysts were prepared including 1) lignin-
SO3Sc(OTf)2, 2) lignin-SO3Cu(OTf), and 3) lignin-IL@NH2 (IL=
ionic liquid). These solid materials were then examined in
many organic transformations. It was finally found that, com-
pared with its homogeneous counterpart as well as some
other solid catalysts that are prepared by using different
supports with the same metal or catalytically active species,
the lignin-supported catalysts showed better performance in
these reactions not only in terms of activity but also with
regard to recyclability.
Introduction
On the other hand, conversion of waste biomass to value-
added materials has gained the attention of academia and in-
dustry. Particularly, in the last five years, a lot of effort has
been devoted to converting lignin, which is one of the major
parts of inedible biomass to valuable materials.[4] Although
many kinds of lignin-based biomass are available, most of the
efforts have been spent on valorization of natural lignin, and
the rational utilization of the other lignin derivatives is far less
studied. The salt of lignosulfonic acid is one of the most impor-
tant lignin derivatives that is produced from an eluted solution
(black liquor) obtained as a byproduct of the cooking process
in sulfite pulping. The sulfonic group of lignosulfonate (LS) is
usually introduced into the a-position of the phenylpropane
structure of lignin by cleavage of the side chain.[5] Molecular
mass of LS ranges from several hundred to several million ac-
cording to the preparation conditions. Since LS consists of
a C6–C3 hydrophobic basic structure with hydrophilic groups,
such as sulfonic, hydroxyl, and carboxyl groups, an aqueous
solution of LS shows amphiphilic properties. In this account,
metal salts of LS have often been used as dispersants in
a wide range of industrial fields.[6] Because LS salts are very
cheap and largely available in the market,[7] value-added con-
versions of sodium lignosulfonate (NaLS, 800000 tons per year)
into fine chemicals have also been explored.[8] However, exis-
tence of sulfur in lignosulfonate precluded the possible appli-
cation of novel metal-based catalysts, such as Pd and Pt, in its
value-added conversions. Strong acid strength of lignosulfonic
acid also allowed its use as either a proton-transfer material for
fuel cells or a Brønsted acid catalyst for hydrolysis of biomass.[9]
Unfortunately, until now, preparation of the acid form of ligno-
sulfonate has had to rely on an energy-intensive procedure.
Recently, we have been interested in rational utilizations of
bio-based chemicals. In a continuation of our research to ex-
plore organic reactions by using bio-based chemicals as alter-
natives to conventional solvents or auxiliaries,[10] we thought it
The synthesis of novel catalysts with well-designed composi-
tion and structure tailored to the requirements of a particular
application is one of the most active fields in catalysis research.
The relationship between structure, organized environment,
and catalytic properties of active species tells us how to estab-
lish a new strategy for the rational design of heterogeneous
catalysts. However, to realize this goal, diversity of solid sup-
port has to be extended as much as possible because the
chemical properties of the support have been shown to play
an important role in determining catalyst activity and selectivi-
ty.[1] Although researchers are now able to manipulate, to
some extent, the morphology and surface character of some
supporting materials, such as metal oxides[2] and resins,[3] with
the increasing demand on task-specific catalysis, especially in
the area of sustainable energy and environmental science,
preparation of new supporting materials with unique proper-
ties that enable researchers to conduct rational design of a cat-
alytic system still remains a big challenge.
[a] S. Sun, Dr. R. Bai, Prof. Dr. Y. Gu
Hubei Key Laboratory of Material Chemistry and Service Failure
Key Laboratory for Large-Format Battery
Materials and System, Ministry of Education
School of Chemistry and Chemical Engineering,
Huazhong University of Science and Technology (HUST)
1037 Luoyu road, Hongshan District, Wuhan 430074, (P.R. China)
Fax: (+86)2787543745
E-mail: bairx@126.com
klgyl@hust.edu.cn
[b] Prof. Dr. Y. Gu
State Key Laboratory for Oxo Synthesis and Selective Oxidation
Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences
Lanzhou, 730000 (P.R. China)
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201303364.
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would be worthwhile to investigate the possibility of using LS
as catalyst support. The reasons are multifold: 1) NaLS is a fine
powder that is quite stable at moderately high temperature
(<2008C) under neutral conditions, and insoluble in most of
the organic solvents; this will facilitate the use and the follow-
ing recycling of the LS-immobilized metal catalyst; 2) a large
amount of sulfonic group in LS enables its use as an anionic
support that can load some cationic species by means of ion
exchange; 3) the skeleton of LS contains various polar func-
tional groups, such as hydroxyl and carboxyl groups, which
might be able to affect the catalytic efficiency synergistically;
and importantly, this kind of synergistic effect, if exists, cannot
be easily attained with some other supporting materials. Out
of these considerations, we have recently started a research
program on this topic. Herein, we disclose the successful out-
come of this endeavor in which lignosulfonate-based support
not only displays an excellent ability to immobilize the select-
ed cationic species, but also confers the formed catalysts an
outstanding performance including high catalytic activity and
good recyclability. This observation opens a new way for ra-
tional utilization of this waste biomass while making benefit of
the heterogenization of homogeneous metal catalysts.
then dried under vacuum at 808C. By means of changing the
mass ratio of NaLS/Sc(OTf)3, two ScIII-modified lignin materials
were obtained, which possess different Sc loadings as shown
in Figure 1. A control experiment, ion exchange of lignin with
Figure 1. Solid-supported catalysts prepared in this work.
Sc(OTf)3, revealed that only a trace amount of Sc was absorbed
onto the unmodified natural lignin, which implied the fact that
the presence of sulfonic groups in NaLS is the key to render
the immobilization possible. Two conventional solid-supported
ScIII reagents were also prepared through an ion exchange
method, which included a silica-supported scandium (SiO2–Sc)
and a resin-supported scandium (Resin–Sc), to understand well
the catalytic efficiency of the LS–Sc materials.
Results and Discussion
To demonstrate the feasibility of using LS as a solid support to
immobilize cationic species, our initial studies started with im-
mobilization of ScIII by using Sc(OTf)3, which has been exten-
sively used as a Lewis acid catalyst in many organic transfor-
mations thanks to a series of original works of Kobayashi in
the 1990s,[11] as the metal source. As Sc(OTf)3 is very expensive
and normally soluble in the reaction mixture, recycling of
Sc(OTf)3 after its use is practically difficult. Therefore, much
effort has recently been paid to the immobilization of this spe-
cies onto solid supports.[12] However, immobilizing ScIII with
solid supports while maintaining the high catalytic activity of
the homogeneous counterpart is not easy because catalytic ac-
tivity of the heterogeneous ScIII catalyst was also affected by
many factors, such as accessibility of substrate to the catalyst
and diffusion of the product into the solvents. Generally, prep-
aration of a highly active solid-supported scandium(III) catalyst
not only needs sophisticated ability on the structural tuning of
the supporting materials, but also requires a good control on
the balance of steady immobilization and maintenance of the
catalytic activity. For these reasons, the reported solid-support-
ed ScIII catalysts, so far, were only used in some high-end appli-
cations, although some of them are commercially available. In
searching for a more practical and efficient approach to the
immobilization of the scandium(III) catalyst, we were attracted
by the unique properties of NaLS. Because it is a cheap and
largely available organic waste product, the strategy of immo-
bilizing ScIII with NaLS, if established, will be a huge incentive
for both academia and industry to use the obtained catalysts.
NaLS was provided by Shanghai Jingchun Industry. Imple-
mentation of our study was started with a simple ion ex-
change of NaLS with Sc(OTf)3 in ethanol. The thereby obtained
solid materials were thoroughly washed with ethanol, and
With all the solid-supported scandium catalysts in hand, we
then examined the catalytic efficiency of these materials in
some organic reactions. In the beginning, we undertook this
study with the implementation of a Michael addition/dehydra-
tion tandem reaction of 3-acetyl-2-hydroxy-2-methylchromene
and indole that might be able to provide densely functional-
ized 4H-chromene derivatives, which have showed various in-
teresting pharmacological properties.[13] Although 3-acetyl-2-
hydroxy-2-methylchromene could be easily obtained through
condensation of salicylaldehyde and acetoacetone,[14] its use as
a Michael acceptor has not been evaluated before. In continua-
tion of our research to synthesize substituted 4H-chromenes,[15]
we envisioned that Michael addition/dehydration tandem reac-
tion of 3-acetyl-2-hydroxy-2-methylchromene with a nucleo-
phile should be a possible way for constructing these hetero-
cycles.
Initial experimentation was undertaken in ethanol by using
1a, 2a, and catalytic amounts of toluenesulfonic acid (PTSA)
under an atmospheric environment, the mixture being heated
at 808C for 8 h (Table 1, entry 1). After reaction, a pale-yellow
solid was obtained by means of isolation with preparative TLC.
The following spectrometric analysis of the sample with NMR
and IR spectroscopy, and HRMS analysis confirmed the struc-
ture of 3a. However, the yield only reached 70% in this case.
No product was obtained under catalyst-free conditions, which
indicated the fact that a catalyst is necessary for this reaction
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reaction time, and the optimal conditions should be 1.2 mol%
of LS–Sc I, 808C, and 8 h (entries 16–18).
Table 1. Michael addition/dehydration tandem reaction of 1a with
indole.[a]
Because LS–Sc is solid, recycling of the catalyst is very easy.
After reaction, the recovered LS–Sc I was washed with ethanol
and dried under vacuum conditions at 608C, and then, subject-
ed to the next run. After three times of reuse, the LS–Sc I cata-
lyst is still capable of catalyzing the model reaction in 90% of
yield (Table 1, entry 7), which indicates that the present LS–Sc
catalyst is quite robust under the reaction conditions. We also
investigated Sc leaching during the reaction. The heterogene-
ous catalyst was isolated by centrifugation after 4 h of reaction
(ca. 65% yield) and the solution phase was allowed to react for
a further 4 h under the same conditions. The yield of 3a was
only 66% after that time, which confirmed that there was
hardly any leaching of Sc into the reaction mixture. ICP-MS
showed that the Sc content of the catalyst did not change ap-
preciably after the reaction. The slight decrease in catalytic ac-
tivity in subsequent runs may be due to the unavoidable loss
of solid catalyst during recovery and washing. Replacing LS–Sc
I with other solid-supported scandium catalysts, such as SiO2–
Sc and Resin–Sc, gives also good results with the fresh cata-
lysts. However, in the second round of recycling the catalysts,
only moderate yields were obtained (entries 19 and 20). ICP-
MS analysis revealed that Sc loadings of the recovered SiO2–Sc
and Resin–Sc catalysts decreased to 0.27 and 0.30 mmolgÀ1
after its use. Although the linkage is the same in all the sup-
ported ScIII catalysts, because of the presence of a lot of
hydoxy and carboxyl groups in the NaLS support, immobilizing
ScIII onto this support was naturally affected by the possible in-
teraction of ScIII with these polar functional groups. This kind
of interaction might play a role in culling, in which only tightly
bonded ScIII can remain in the support, and some ScIII species
trapped by the support through relatively weak interactions
were removed; this behavior ensures the immobilized ScIII
stays steadily in the support even under the reaction condi-
tions; however, in the case of SiO2 and resin supports, due to
a lack of such a kind of culling effect, a part of the immobilized
ScIII species might break away from the support with the aid of
an interaction with polar substrates, thus resulting in leaching
of ScIII. All these results indicated that 1) the properties of sup-
porting materials are indeed crucial for maximizing the catalyt-
ic efficiency of the scandium catalyst and 2) NaLS is a preferable
support, compared with silica and resin, for immobilizing
Sc(OTf)3 when the obtained catalyst was utilized in the model
reaction. It is worth noting that the reaction can also be effec-
tively scaled up with similar efficiency. For example, the
10 mmol scale reaction of 1a with 2a gave the corresponding
4H-chromene 3a in 91% yield (entry 21) by using the same
catalyst, LS–Sc I. This result not only demonstrated the feasibil-
ity of using lignin-supported metal as a practical catalyst, but
also manifested the great potential of the model reaction in
organic synthesis.
Entry
Cat.
Cat. amount [mol%]
Solvent
Yield [%]
1
2
3
4
5
6
7
8
PTSA
–
ZnCl2
LiBr
1.2
0
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
70
0
15
26
80
90
93 (90)[b]
0
0
34
81
75
65
84
30
1.2
1.2
1.2
1.2
1.2
–
FeCl3
Sc(OTf)3
LS–Sc I
lignin
9
NaLS
–
EtOH
EtOH
10
11
12
13
14
15
16
17[c]
18[d]
19
20
21
LS–Sc II
LS–Sc I
LS–Sc I
LS–Sc I
LS–Sc I
LS–Sc I
LS–Sc I
LS–Sc I
LS–Sc I
SiO2–Sc
Resin–Sc
LS–Sc I
1.2
1.2
1.2
1.2
1.2
1.2
0.6
1.2
1.2
1.2
1.2
1.2
CH3NO2
CH3CN
1,4-dioxane
DCE
toluene
EtOH
EtOH
EtOH
EtOH
EtOH
41
43
65
92 (50)[b]
87 (63)[b]
91[e]
EtOH
[a] 1a: (0.5 mmol), 2a: (0.6 mmol), solvent: (1 mL). [b] The yield in paren-
thesis showed reuse of the catalyst in the third run. [c] Reaction tempera-
ture: 508C. [d] Reaction time: 4 h. [e] The reaction was performed in
10 mmol scale. DCE=dichloroethane.
(entry 2). In the presence of weak Lewis acids, such as ZnCl2
and LiBr, the reaction proceeded sluggishly, and 3a was ob-
tained in less than 30% of yields (entries 3 and 4). The reaction
rate can be significantly improved by using strong Lewis acids,
such as FeCl3 and Sc(OTf)3, as catalysts, and the reaction yields
reached 80 and 90%, respectively, under identical conditions
(entries 5 and 6). Some solid catalysts were examined later on.
Interestingly, a maximum yield, 93%, was obtained with a het-
erogeneous scandium catalyst, LS–Sc I (entry 7). The reaction
was also performed over lignin and NaLS systems, and no 3a
was detected in these cases (entries 8 and 9). All these results
indicated that the immobilized scandium is responsible for the
good performance of LS–Sc I. When LS–Sc II, which possesses
a lower Sc loading than that of LS–Sc I, was used in the reac-
tion, only a moderate yield was obtained under the identical
conditions (entry 10), which implied the fact that scandium
loading on the NaLS support was also able to significantly
affect the catalytic activity of the prepared lignin-immobilized
metal catalyst. The effect of the organic solvents on the model
reaction was also examined, in which ethanol and acetonitrile
gave high yields (entries 11–15). For safety and environmental
reasons, we continued the reactions with ethanol. Further in-
vestigation revealed that the reaction was also affected by the
other parameters including catalyst amount, temperature, and
With the optimized conditions in hand, we probed the
scope of the reaction with respect to both the 3-acetyl-2-hy-
droxy-2-methylchromene and the indole components. As evi-
denced by the results in Figure 2, 3-acetyl-2-hydroxy-2-methyl-
chromenes with different substituents smoothly reacted with
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gave only a moderate yield, the
selectivity to the ring-opening
product, 7a, over this catalyst
was very high (entry 2). De-
crease of the catalyst amount
from 10 to 5 mol% resulted in
a significant loss of the reaction
yield (entry 3). Remarkably, be-
cause the model ring-opening
reaction was known to be sus-
ceptible to the acid strength of
the catalyst, applying the ho-
mogeneous counterpart of the
LS–Sc I catalyst, Sc(OTf)3, in this
reaction resulted in formation
of a very messy mixture. As
a result, the yield of 7a ob-
tained in this case was only
23% under identical conditions
(entry 4). This result also indicat-
ed that immobilizing Sc(OTf)3
onto the NaLS support might
either be able to tune the Lewis
Figure 2. Substrate scope for the model Michael/dehydration tandem reaction catalyzed by LS–Sc I.
indoles, producing the corresponding densely substituted 4H-
chromene products in generally good to excellent yields. Both
electron-rich and moderately electron-poor indoles readily par-
ticipated in the reaction. However, indoles containing a strongly
electron-withdrawing group, such as carboxyl, failed to partici-
pate in the reaction, likely due to their poor reactivity. This se-
quential reaction can also be extended, over LS–Sc I catalyst,
to another carbon-based nucleophile, antipyrine, affording the
hitherto unreported 4-(3-acetyl-2-methyl-4H-chromen-4-yl)anti-
pyrine 5a in good yield (Scheme 1).
acidity of the ScIII species, or be capable of offering a synergistic
effect between the support and ScIII species that is responsible
for the enhancement of the reaction selectivity. This point de-
serves further investigation. Screening of the reaction solvents
revealed that the best one is nitromethane. In this solvent, LS–
Sc I is insoluble at the end of the reaction, thus facilitating the
recovery of the catalyst (entries 5 to 8). Reuse experiments
demonstrated that LS–Sc I can be reused at least twice in the
model ring-opening reaction without significant loss of its ac-
tivity (entries 9 and 10). However, it should be noted that nitro-
methane is toxic and explosive solvent, which diminished to
some extent the greenness of this system. Fortunately, green
Table 2. LS–Sc-catalyzed electrophilic ring-opening reactions of 2-butoxy-
3,4-dihydropyran with indoles.[a]
Scheme 1. LS–Sc-catalyzed Michael addition/dehydration tandem reaction of
1a and antipyrine.
To extend the utility of this catalyst, we then examined
some other reactions with LS–Sc catalyst. The second reaction
we investigated was electrophilic ring-opening reactions of 2-
butoxy-3,4-dihydropyran with indoles. This type of reaction is
an acid-catalyzed reaction, but proved to be very sensitive to
the acid strength of the catalyst.[16] Previously, it has been suc-
cessfully performed in the presence of manganese(II) halides,
such as MnCl2 and MnBr2.[17] However, these catalysts cannot
be recycled after the reaction. We examined the performance
of the LS–Sc catalyst in this type of reaction, and the results
are listed in Table 2. To our delight, LS–Sc I can indeed effec-
tively catalyze the model ring-opening reaction and an 89%
yield could be obtained (Table 2, entry 1). Although LS–Sc II
Entry
Cat.
Solvent
T [8C]
Yield [%]
1
2
3[b]
4
5
6
7
LS–Sc I
LS–Sc II
LS–Sc I
Sc(OTf)3
LS–Sc I
LS–Sc I
LS–Sc I
LS–Sc I
LS–Sc I
CH3NO2
CH3NO2
CH3NO2
CH3NO2
EtOH
CH3CN
1,4-dioxane
DCE
100
100
100
100
80
80
100
80
89
45
69
23
trace
trace
<10%
trace
88
8
9[c]
CH3NO2
100
[a] 6a: (0.5 mmol, indole: 1.25 mmol, Sc catalyst, 10 mol%, solvent: 1 mL,
1008C, 11 h. [b] Sc catalyst: 5 mol%. [c] The catalyst was used in the third
time.
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ple, for the synthetic reaction of
9a, only a 66% yield was ob-
tained with triflic acid.[19c] By
using sulfamic acid as a catalyst,
the yield reached 83%; howev-
er, a longer reaction time, 8 h,
was needed.[19f] Although glu-
conic acid gave a comparable
yield with that of LS–Sc I, it was
used, unfortunately, as a sol-
vent.[10a] Some solid catalysts
have also been evaluated,[20]
however, because their prepara-
tions are not always easy, our
present system thus offers
a cost-effective and easily acces-
sible alternative to the previous-
ly reported solid catalysts.
The LS–Sc catalyst also
showed a good catalytic activity
in ethanol in the condensation
of anthranilamide and cyclic ke-
Figure 3. Substrate scope of ring-opening of 2-butoxy-3,4-dihydropyrans with indoles catalyzed by LS–Sc I.
chemists already started to work on the replacement of nitro-
methane with environmentally benign solvents, and a recent
advance is a class of nitrofunctionalized imidazolium salts that
was proved to be able to replace nitromethane while keeping
its efficiency in acid catalysis.[18] Although the reported imida-
zolium salts are not compatible with LS–Sc catalyst (suffer
from a solubility problem), we believe that this problem can
be overcome in the future because of the rapid development
of green solvents.
tones, thus providing an ecofriendly route for the synthesis of
2-substituted-2,3-dihydroquinazolin-4(1H)ones
(Scheme 3).[21]
Later on, substrate scope was also investigated under the
optimized conditions. As shown in Figure 3, all the examined
2-butoxy-3,4-dihydropyrans and indoles readily participated in
the ring-opening reactions, and random combination of the
starting materials could give the final products with up to 96%
yield. These results indicated again the usefulness of the LS–Sc
catalyst for organic transformations.
Scheme 3. Condensation of anthranilamide and cyclic ketones catalyzed by
LS–Sc I.
All the above-mentioned examples demonstrated that LS–Sc
can indeed be used as an efficient and recyclable solid catalyst
for organic transformations. Considering the fact that previous
methods for immobilizing Sc(OTf)3 onto solid support were
generally associated with some supporting materials that were
either expensive or not commercially available, the present
method thus provided a cost-effective and practically feasible
route for heterogenizing Sc(OTf)3 catalyst.
Similarly, a Friedel–Crafts-type reaction of a-methyl-4-me-
thoxybenzyl alcohol, 8a, and indoles performed also very well
in the presence of LS–Sc I catalyst, providing 3-benzylindole
derivatives, 9a–c, in high yields (Scheme 2). LS–Sc I catalyst
could be reused at least twice without significant loss of its ac-
tivity. Although many catalyst systems have been used in
these types of reactions before, most of which are homogene-
ous Brønsted or Lewis acids that cannot be recycled and
reused, some of the reported systems lack efficiency. For exam-
To further explore the potential utility of our strategy for use
of NaLS as an anionic solid support, we then applied this mate-
rial to the immobilization of copper(II) catalyst. As we expect-
ed, NaLS support is indeed amenable to heterogenizing CuII
species when Cu(OTf)2 was used as the copper
source. The obtained LS–Cu catalyst was proved to
be highly active for catalyzing the three-component
click reaction of NaN3, phenylacetylenes, and benzyl
halides along with 20 mol% of sodium ascorbate
(Table 3). The desired cycloaddition products were
obtained in yields ranging from 88 to 99% with ex-
clusive 1,4-regioselectivity. Previously, various solid
copper catalysts, such as ammonium salt-tagged N-
heterocyclic carbene (NHC)–CuI complexes,[22g] cross-
Scheme 2. Friedel–Crafts-type reaction of 8a with indoles catalyzed by LS–Sc I.
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Table 3. LS–Cu-catalyzed three-component click reaction of NaN3, phe-
nylacetylenes and benzyl halides.[a]
entry
X
R1
R2
Product
Yield [%]
Scheme 5. LS–Cu-catalyzed oxidative coupling of N,N-dimethylaniline and
indole.
1
2
3
4
5
6
7
8
9
Br
Cl
Br
Br
Br
Br
Br
Br
Br
Br
H
H
NO2
H
H
H
H
H
H
H
H
H
Me
Et
n-Pr
nBu
n-amyl
OMe
tBu
12a
12a
12b
12c
12d
12e
12 f
12g
12h
12i
96 (94)[b]
88
96
99
99
98
97
99
Finally, another lignosulfonate, ammonium lignosulfonate
(NH4LS), was used to immobilize an amine-functionalized imid-
azolium-based ionic liquid by the ion exchange method, and
the obtained material was defined as LS-IL@NH2 (see Figure 1).
LS-IL@NH2 showed a good catalytic ability to promote a Knoe-
vengal reaction between 4-chlorobenzaldehyde 16a and malo-
nonitrile 17a. As before, LS-IL@NH2 catalyst could be reused
many times without significant loss of its catalytic activity. In-
terestingly, with LS-IL@NH2 catalyst, the yield of the desired
product 18a is much higher than that of another commercially
available natural base catalyst, chitosan, under the identical
conditions. This is quite reasonable considering the fact the
ion-exchange procedure ensures all the imidazolium cations
stay on the positions that are easily accessible in the support,
which allows the substrate contact easily with the NH2 group
in LS-IL@NH2. However, most of the NH2 groups of chitosan
were blocked by a hard backbone constructed by multiple hy-
drogen bond interaction between the glucose monomers.[24]
This example not only manifested the effectiveness of LS-
IL@NH2, but also demonstrated that LS is indeed a versatile
support for immobilizing homogeneous catalysts (Scheme 6).
96
60
10
H
[a] (Bromomethyl)benzene: 0.30 mmol, ethynylbenzene: 0.36 mmol,
NaN3: 0.40 mmol, Cu catalyst, 5 mol%, sodium ascorbate: 20 mol%, etha-
nol: 1 mL, 808C, 8 h. [b] Cu catalyst was used the third time.
linked polymeric ionic liquid material supported copper,[22h]
and glutathione bearing nanoferrites,[22i] have been developed
in this type reaction, sometimes with remarkable results.[22] Our
LS–Cu catalyst showed, however, its inherent advantages in
the following aspects: 1) cost-effectiveness of the supporting
material and 2) simple operation for preparing the catalyst. Be-
sides, taking the fact that Cu(OTf)2 is now an easily available
copper salt into account, it is not unreasonable to expect that
LS–Cu catalyst might be a preferable choice for researchers
who needed a heterogenized copper(II) catalyst. With this in
mind, two other reactions were then examined by using LS–Cu
as the catalyst. As shown in Scheme 4, more than 90% of
Scheme 4. LS–Cu-catalyzed Glaser reaction of phenylacetylenes.
Scheme 6. LS–AIL-catalyzed Knoevenagel reaction of 4-chlorobenzaldehyde
and malononitrile.
yields could be obtained in Glaser reactions of phenylacety-
lenes, in which LS–Cu catalyst is also recyclable. Oxidative cou-
pling of N,N-dimethylaniline and indole proceeded also very
well in the presence of LS–Cu catalyst (Scheme 5) bearing in
mind the fact that only 73% of yield was obtained over expen-
sive ruthenium porphyrins catalysts.[23] The mechanism of this
reaction most likely involves the formation of formaldehyde
through oxidation of the methyl group of N,N-dimethylaniline
14a, which followed by an electrophilic alkylation reaction.[23]
All these results demonstrated that LS–Cu is indeed a versatile
heterogeneous catalyst for organic transformations.
Conclusion
Lignosulfonates were used, for the first time, as a solid support
of cationic catalysts. This protocol was proved to be amenable
to the immobilizations of Sc(OTf)3, Cu(OTf)2, and an amine-
functionalized imidazolium-based ionic liquid. The obtained
catalysts were then successfully applied to many organic trans-
formations, in which the catalysts showed not only high activi-
ty but also good recyclability. In some cases, synergistic effects
between the metal species and lignosulfonate support were
also observed, which conferred the catalyst a salient ability
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duced pressure. Then, the desired product, 3a, was obtained in
93% yield (177.6 mg) by isolation with preparative TLC (eluting sol-
vent: ethyl acetate/petroether=1:5 (v/v)). Tests for substrate scope
were all performed with an analogous procedure. The recovered
catalyst was dried in air and directly used in the next run. The
large-scale reaction was also performed in the same procedure.
that cannot be attained with other supporting materials. Be-
cause LS is a cheap waste biomass, the use of LS as the sup-
porting material ensures a bonus of practicability, sustainability,
and safety to the processes which deals with the LS-based cat-
alysts. In fact, our strategy stems upon the unexpected capaci-
ty of LS material for cationic exchange. Inspired by this obser-
vation, some other technologies might be developed with the
aid of using metal salts of lignosulfanic acid as anionic
supports.
Spectroscopic data of new compounds
However, the use of NaLS support is also suffering from
some limitations: 1) because LS is soluble in water, the cata-
lysts prepared with this strategy may not be suitable to use in
aqueous conditions taking into consideration their recycling,
2) due to the possible degradation, durability of the obtained
catalysts needed to be further improved, especially when the
catalysts were used in harsh conditions; condensation of ligno-
sulfonate with formalin under acidic conditions can be one of
the suitable methods to strengthen the stability of the ligno-
sulfonate catalyst,[25] 3) in some cases, special attention should
be paid to the reactivity of lignosulfanate support because
there are a large amount of functionalities in the matrix of LS,
which otherwise will affect negatively the reaction outcomes
under appropriate conditions. Furthermore, the structure of
lignin may change according to the season and its origin, the
potential effects of these factors on the catalytic behavior of
lignin support should also be considered.
1-[6-Bromo-4-(1H-indol-3-yl)-2-methyl-4H-chromen-3-yl]etha-
none (3a): Brown liquid; H NMR (400 MHz, CDCl3, 258C, TMS): d=
1
2.13 (s, 3H), 2.42 (s, 3H), 5.27 (s, 1H), 6.87 (d, J=8.8 Hz, 1H), 6.93
(d, J=2.4 Hz, 1H), 7.09–7.19 (m, 3H), 7.26 (d, J=8.0 Hz, 1H), 7.30
(d, J=2.4 Hz, 1H), 7.62 (d, J=2.4 Hz, 1H), 8.31 ppm (s, 1H);
13C NMR (100 MHz, CDCl3): d=19.7, 29.6, 33.0, 111.5, 113.6, 116.4,
117.9, 118.5, 120.0, 120.4, 122.2, 122.6, 125.5, 127.1, 130.4, 131.5,
136.5, 148.1, 157.5, 199.6 ppm; IR: n˜ =3401, 3351, 3057, 2923,
2247, 1884, 1677, 1618, 1569, 1477, 1738, 1240, 1185, 1041, 941,
907, 816, 737, 651, 626, 524, 424 cmÀ1; HRMS (ESI): m/z: calcd for
C20H16BrNNaO2: 404.0262 [M+Na]+; found: 404.0251.
1-[6-Bromo-2-methyl-4-(2-methyl-1H-indol-3-yl)-4H-chromen-3-
yl]ethanone (3b): Brown liquid; 1H NMR (400 MHz, CDCl3, 258C,
TMS): d=2.10 (s, 3H), 2.33 (s, 3H), 2.37 (s, 3H), 5.33 (s, 1H), 6.87 (d,
J=8.0 Hz, 1H), 7.02–7.09 (m, 3H), 7.16–7.20 (m, 2H), 7.45 (d, J=
7.2 Hz, 1H), 8.06 ppm (s, 1H); 13C NMR (100 MHz, CDCl3): d=11.8,
19.5, 29.8, 31.7, 110.4, 113.0, 115.5, 116.4, 117.5, 117.7, 119.8, 121.1,
126.5, 127.2, 130.4, 131.7, 131.8, 135.0, 149.1, 156.2, 199.7 ppm; IR:
n˜ =3396, 3057, 3025, 2978, 2921, 2247, 1880, 1679, 1619, 1570,
1477, 1380, 1237, 940, 814, 738, 433 cmÀ1; HRMS (ESI): m/z: calcd
for C21H18BrNNaO2: 418.0419 [M+Na]+; found: 418.0416.
Despite these drawbacks, by means of a careful control on
balancing every important factor, LS support has been proved
to be a potential candidate to be applied in many organic re-
actions in combination with immobilizing cationic catalysts. In
the future, these problems might be partially solved by com-
positing LS with some other materials. If such methods were
established, considering the low cost and the unique capacity
of LS, it is not unreasonable to expect that the use of LS as
a supporting material or one component of supporting materi-
als will constitute a new facet of catalysis research. We are
now actively working on this line.
1-[6-Bromo-4-(5-methoxy-1H-indol-3-yl)-2-methyl-4H-chromen-3-
yl]ethanone (3c): Brown liquid; 1H NMR (400 MHz, CDCl3, 258C,
TMS): d=2.16 (s, 3H), 2.42 (s, 3H), 3.82 (s, 3H), 5.22 (s, 1H), 6.81
(dd, Ja =2.4, Jb =8.8 Hz, 1H), 6.92–6.94 (m, 2H), 7.03–7.05 (m, 2H),
7.13–7.17 (m, 2H), 8.32 ppm (s, 1H); 13C NMR (100 MHz, CDCl3): d=
19.7, 29.6, 33.1, 55.7, 100.5, 112.1, 112.1, 113.4, 117.4, 120.1, 123.2,
125.8, 126.6, 127.5, 128.5, 128.9, 131.7, 147.7, 154.1, 157.6 ppm; IR:
n˜ =3353, 3055, 2996, 2939, 2249, 1873, 1679, 1623, 1576, 1482,
1379, 1241, 1220, 1043, 941, 908, 818, 732, 651, 552, 474, 429 cmÀ1
HRMS (ESI): m/z: calcd for C21H18BrNNaO3: 434.0368 [M+Na]+;
;
found: 434.0360.
Experimental Section
1-[6-Bromo-4-(5-bromo-1H-indol-3-yl)-2-methyl-4H-chromen-3-
yl]ethanone (3d): Brown liquid, 1H NMR (400 MHz, CDCl3, 258C,
TMS):d=2.15 (s, 3H), 2.42 (s, 3H), 5.23 (s, 1H), 6.91 (d, J=8.0 Hz,
1H), 6.97 (d, J=2.4 Hz, 1H), 7.14 (d, J=8.0 Hz, 1H), 7.18–7.32 (m,
5H), 7.71 (d, J=1.2 Hz, 3H), 7.71 (d, J=8.0 Hz, 1H), 8.42 ppm (s,
1H); 13C NMR (100 MHz, CDCl3): d=19.8, 29.8, 32.8, 112.9, 113.3,
113.6, 116.5, 118.1, 120.3, 121.0,123.8, 125.2, 126.7, 127.2, 130.6,
131.4, 135.0, 148.1, 157.7, 199.3 ppm; IR: n˜ =3344, 3066, 2926,
2249, 1673, 1620, 1567, 1476, 1238, 908, 817, 733, 644, 587,
420 cmÀ1; HRMS (ESI): m/z: calcd for C20H15Br2NNaO2: 481.9367
[M+Na]+; found: 481.9355.
General
Typical procedure for the preparation of LS–Sc catalyst: Sodium
ligninsulfonate (1.5 g) and Sc(OTf)3 (700 mg, 1.4 mmol) was mixed
with anhydrous ethanol (30 mL) in a 100 mL round-bottomed flask.
The mixture was then stirred at 808C for 36 h. After the reaction
was completed, the solid was obtained by filtration and then
washed with ethanol (50ꢁ5 mL). After drying, the loading of scan-
dium was measured by ICP-MS, and the value was 0.44 mmolgÀ1
(LS–Sc I).
Typical procedure for catalytic reaction: All reactions were con-
ducted in a 10 mL of V-type flask equipped with triangle magnetic
stirring. In a typical reaction, the prepared starting material 1a
1-[6-Bromo-2-methyl-4-(6-methyl-1H-indol-3-yl)-4H-chromen-3-
yl]ethanone (3e): Brown liquid; 1H NMR (400 MHz, CDCl3, 258C,
TMS): d=2.12 (s, 3H), 2.39 (s, 3H), 2.41 (d, J=1.2 Hz, 3H), 5.21 (s,
1H), 6.83–6.86 (m, 2H), 6.94 (d, J=8.4 Hz, 1H), 7.03 (s, 1H), 7.15
(dd, Ja =4.0, Jb =8.0 Hz, 1H), 7.29 (s, 1H), 7.49 (d, 1H), 8.25 ppm (s,
1H); 13C NMR (100 MHz, CDCl3): d=19.7, 21.5, 29.5, 33.0, 111.4,
113.5, 116.3, 117.8, 118.0, 120.2, 121.7, 121.9, 123.3, 127.1, 130.3,
131.5, 132.0, 136.9, 148.0, 157.5, 199.7 ppm; IR: n˜ =3402, 2919,
2861, 2248, 1876, 1677, 1621, 1568, 1476, 1378, 1240, 1219, 908,
(0.50 mmol) was mixed with 2a (0.60 mmol) and LS–Sc
I
(1.2 mol%) in anhydrous ethanol (1.0 mL) for 8 h at 808C. After re-
action, the mixture was cooled to room temperature, and then
centrifuged. The supernatant organic phase was isolated and the
bottom solid was washed with ethanol (1.0 mLꢁ2). All organic
phases were then combined together and concentrated under re-
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802, 733, 647, 484, 430 cmÀ1
;
HRMS (ESI): m/z: calcd for
125.7, 136.6, 147.0, 147.1, 158.8, 199.8 ppm; IR: n˜ =3413, 3056,
C21H18BrNNaO2: 418.0419 [M+Na]+; found: 418.0417.
2961, 2869, 2247, 1674, 1575, 1496, 1359, 1218, 916, 824, 739, 605,
425 cmÀ1
; HRMS (ESI): m/z: calcd for C24H25NNaO2: 382.1783
1-[6-Bromo-2-methyl-4-(1-methyl-2-phenyl-1H-indol-3-yl)-4H-
chromen-3-yl]ethanone (3 f): Brown liquid; 1H NMR (400 MHz,
CDCl3, 258C, TMS): d=1.98 (s, 3H), 2.01 (s, 3H), 3.41 (s, 3H), 5.36 (s,
1H), 6.76 (d, J=8.0 Hz, 1H), 7.01 (d, J=4.0 Hz, 1H), 7.07 (s, 1H),
7.11–7.31 (m, 5H), 7.42 (s, 3H), 7.71 ppm (d, J=8.0 Hz, 1H);
13C NMR (100 MHz, CDCl3): d=19.2, 29.8, 30.3, 31.9, 109.5, 112.5,
116.9, 117.2, 118.2, 120.0, 121.8, 126.3, 126.7, 127.4, 128.2, 128.5,
128.6, 130.7, 131.5, 136.4, 138.9, 147.4, 155.7, 199.5 ppm; IR: n˜ =
3055, 2928, 2248, 1882, 1683, 1610, 1574, 1477, 1359, 1240, 1218,
908, 817, 735, 546 cmÀ1; HRMS (ESI): m/z: calcd for C27H22BrNNaO2:
494.0732 [M+Na]+; found: 494.0714.
[M+Na]+; found: 382.1775.
1-[4-(1H-Indol-3-yl)-2,8-dimethyl-4H-chromen-3-yl]ethanone (3l):
Brown liquid; 1H NMR (400 MHz, CDCl3, 258C, TMS): d=2.12 (s,
3H), 2.23 (s, 3H), 2.47 (s, 3H), 5.30 (s, 1H), 6.79–6.84 (m, 2H), 6.91
(d, J=7.2 Hz, 1H), 7.06–7.12 (m, 3H), 7.18–7.20 (m, 1H), 7.69–7.71
(m, 1H), 8.28 ppm (s, 1H); 13C NMR (100 MHz, CDCl3): d=15.3, 19.5,
29.1, 32.8, 111.0, 113.4, 118.2, 119.3, 121.0, 121.6, 122.6, 123.3,
124.5, 124.9, 125.3, 125.8, 128.3, 136.1, 147.0, 158.0, 199.7 ppm; IR:
n˜ =3412, 3346, 3055, 2922, 2247, 1676, 1578, 1467, 1378, 1247,
1197, 1091, 936, 909, 739, 649, 425 cmÀ1; HRMS (ESI): m/z: calcd for
C21H19NNaO2: 340.1313 [M+Na]+; found: 340.1305.
1-[6-Chloro-4-(1H-indol-3-yl)-2-methyl-4H-chromen-3-yl]etha-
1
none (3g): Brown liquid; H NMR (400 MHz, CDCl3, 258C, TMS): d=
1-[4-(1H-Indol-3-yl)-8-methoxy-2-methyl-4H-chromen-3-yl]etha-
none (3m): Brown liquid; 1H NMR (400 MHz, CDCl3, 258C, TMS):
d=2.15 (s, 3H), 2.50 (s, 3H), 3.87 (s, 3H), 5.32 (s, 1H), 6.67–6.69 (m,
1H), 6.84–6.86 (s, 2H), 6.93 (d, J=2.4 Hz, 3H), 7.12–7.14 (m, 2H),
7.25–7.27 (m, 1H), 7.70–7.72 (m, 1H), 8.27 ppm (s, 1H); 13C NMR
(100 MHz, CDCl3): d=19.8, 29.5, 33.0, 56.0, 109.6, 111.3, 113.8,
118.6, 119.8, 120.3, 121.3, 122.0, 122.6, 123.9, 125.7, 126.2, 136.4,
138.7, 147.5, 157.9, 199.7 ppm; IR: n˜ =3403, 3056, 2933, 2840,
2248, 1675, 1576, 1483, 1330, 1204, 1094, 910, 738, 646, 600,
2.13 (s, 3H), 2.42 (s, 3H), 5.27 (s, 1H), 6.91–6.93 (m, 2H), 7.03 (dd,
Ja =2.4, Jb =8.8 Hz, 1H), 7.10–7.16 (m, 3H), 7.26 (d, J=7.6 Hz, 1H),
7.62 (d, J=7.6 Hz, 1H), 8.36 ppm (s, 1H); 13C NMR (100 MHz,
CDCl3): d=19.7, 29.6, 33.0, 111.5, 113.5, 117.5, 118.4, 119.9, 120.4,
122.2, 122.6, 125.5, 126.6, 127.5, 128.5, 128.8, 136.5, 147.6, 157.7,
199.7 ppm; IR: n˜ = 3403, 3354, 3058, 2924, 2248, 1883, 1677, 1619,
1572, 1480, 1357, 1241, 1221, 907, 818, 737, 654, 424 cmÀ1; HRMS
(ESI): m/z: calcd for C20H16ClNNaO2: 360.0767 [M+Na]+; found:
360.0755.
425 cmÀ1
; HRMS (ESI): m/z: calcd for C21H19NNaO3: 356.1263
[M+Na]+; found: 356.1255.
1-[6-Chloro-2-methyl-4-(2-methyl-1H-indol-3-yl)-4H-chromen-3-
yl]ethanone (3h): Brown liquid; 1H NMR (400 MHz, CDCl3, 258C,
TMS): d=2.09 (s, 3H), 2.30 (s, 3H), 2.37 (s, 3H), 5.32 (s, 1H), 6.90–
6.95 (m, 2H), 7.00–7.08 (m, 3H), 7.17 (d, J=7.6 Hz, 1H), 7.46 (d, J=
7.6 Hz, 1H), 8.09 ppm (s, 1H); 13C NMR (100 MHz, CDCl3): d=11.8,
19.5, 29.7, 31.8, 110.4, 112.9, 115.5, 117.3, 117.5, 119.7, 121.1, 127.2,
127.5, 128.8, 128.8, 131.8, 134.9, 147.5, 156.4, 199.9 ppm; IR: n˜ =
3395, 3058, 2922, 2247, 1879, 1679, 1619, 1573, 1479, 1225, 907,
817, 735, 652, 428 cmÀ1; HRMS (ESI): m/z: calcd for C21H18ClNNaO2:
374.0924 [M+Na]+; found: 374.0910.
1-[4-(1H-Indol-3-yl)-2,6,8-trimethyl-4H-chromen-3-yl]ethanone
1
(3n): Brown liquid; H NMR (400 MHz, CDCl3, 258C, TMS): d=2.01
(s, 3H), 2.14 (s, 3H), 2.27 (s, 3H), 2.47 (s, 3H), 5.26 (s, 1H), 6.74 (s,
1H), 6.86–6.90 (m, 2H), 7.10–7.13 (m, 2H), 7.22–7.23 (m, 1H), 7.70–
7.71 (m, 1H), 8.28 ppm (s, 1H); 13C NMR (100 MHz, CDCl3): d=15.2,
19.6, 20.2, 29.1, 32.8, 110.9, 113.3, 118.3, 119.3, 121.2, 121.5, 122.1,
124.1, 124.6, 125.3, 125.9, 132.6, 136.0, 145.0, 158.1, 199.5 ppm; IR:
n˜ =3411, 3347, 2921, 2247, 1675, 1584, 1482, 1378, 1212, 1150,
932, 909, 739, 652, 552, 423 cmÀ1; HRMS (ESI): m/z: calcd for
C22H21NNaO2: 354.1470 [M+Na]+; found: 354.1462.
1-[4-(1H-Indol-3-yl)-2-methyl-4H-chromen-3-yl]ethanone
(3i):
1
Brown liquid; H NMR (400 MHz, CDCl3, 258C, TMS): d=2.11 (s, 3H),
2.43 (s, 3H), 5.30 (s, 1H), 6.82 (d, J=2.4 Hz, 1H), 6.87 (t, 1H), 6.98
(d, J=8.0 Hz, 1H), 7.04 (d, J=7.6 Hz, 1H), 7.09–7.11 (m, 2H), 7.19 (t,
2H), 7.67–7.69 (t, 1H), 8.34 ppm (s, 1H); 13C NMR (100 MHz, CDCl3):
d=19.8, 29.4, 32.9, 111.4, 113.7, 116.0, 118.5, 119.6, 121.1, 121.9,
122.6, 124.2, 125.1, 125.6, 127.3, 128.7, 136.4, 148.9, 158.0,
200.1 ppm; IR: n˜ =3408, 3057, 2924, 2247, 1798, 1675, 1619, 1574,
1486, 1378, 1218, 939, 908, 739, 647, 597, 425 cmÀ1; HRMS (ESI):
m/z: calcd for C20H17NNaO2: 326.1157 [M+Na]+; found: 326.1154.
4-(3-Acetyl-6-bromo-2-methyl-4H-chromen-4-yl)-5-methyl-2-
phenyl-1H-pyrazol-3(2H)one (5a): Yellow liquid; 1H NMR
(400 MHz, CDCl3, 258C, TMS): d=2.11 (s, 3H), 2.31 (s, 3H), 2.36 (s,
3H), 3.01 (s, 3H), 5.16 (s, 1H), 6.86 (d, J=8.0 Hz, 1H), 7.23–7.28 (m,
2H), 7.36 (d, J=6.4 Hz, 3H), 7.43 ppm (t, J=8.0 Hz, 2H); 13C NMR
(100 MHz, CDCl3): d=10.7, 19.5, 29.6, 29.7, 35.4, 111.6, 113.5, 116.6,
117.6, 123.9, 125.3, 126.5, 129.1, 130.7, 131.5, 134.7, 148.4, 153.4,
157.8, 164.4, 199.6 ppm; IR: n˜ =3062, 2923, 2240, 1733, 1660, 1478,
1239, 940, 730, 648, 591, 500 cmÀ1; HRMS (ESI): m/z: calcd for
C23H21BrN2NaO3: 475.0633 [M+Na]+; found: 475.0619.
1-[4-(1H-Indol-3-yl)-6-methoxy-2-methyl-4H-chromen-3-yl]etha-
1
none (3j): Brown liquid; H NMR (400 MHz, CDCl3, 258C, TMS): d=
Ethyl 2-acetyl-5,5-bis(5-bromo-1H-indol-3-yl)pentanoate (7c):
1
2.14 (s, 3H), 2.44 (s, 3H), 3.60 (s, 3H), 5.29 (s, 1H), 6.62–6.65 (m,
1H), 6.74–6.75 (m, 1H), 6.91–6.94 (m, 2H), 7.09–7.13 (m, 2H), 7.22–
7.25 (m, 1H), 7.67–7.69 (m, 1H), 8.37 ppm (s, 1H); 13C NMR
(100 MHz, CDCl3): d=19.9, 29.5, 33.4, 55.3, 111.3, 112.8, 113.0, 113.1,
116.8, 118.5, 119.7, 121.0, 122.0, 122.4, 125.6, 125.8, 136.4, 143.1,
155.9, 158.4, 199.7 ppm; IR: n˜ =3409, 3349, 3057, 2930, 2836, 2248,
Brown liquid; H NMR (400 MHz, CDCl3, 258C, TMS): d=1.20 (t, J=
7.2 Hz, 3H), 1.84–1.96 (m, 2H), 2.06–2.12 (m, 2H), 2.14 (s, 3H), 3.47
(t, J=6.0 Hz, 1H), 4.15 (dd, Ja =7.2, Jb =14.4 Hz, 2H), 4.27 (t, J=
7.2 Hz, 1H), 6.86 (d, J=6.8 Hz, 2H), 7.12 (dd, Ja =8.8, Jb =26.0 Hz,
4H), 7.60 (s, 2H), 8.22 ppm (s, 2H); 13C NMR (100 MHz, CDCl3): d=
14.0, 26.6, 28.9, 32.5, 33.7, 59.5, 61.5, 112.1, 112.8, 118.0, 118.2,
121.6, 122.9, 124.5, 128.2, 128.2, 135.1, 169.8, 203.8 ppm; IR n˜ =
3421, 3076, 2981, 2933, 2251, 1855, 1731, 1708, 1559, 1459, 1214,
1097, 909, 884, 796, 732, 585, 422 cmÀ1; HRMS (ESI): m/z: calcd for
C25H24Br2N2NaO3: 581.0051 [M+Na]+; found: 581.0032.
1675, 1582, 1495, 1427, 1215, 1036, 928, 742, 640, 601, 424 cmÀ1
;
HRMS (ESI): m/z: calcd for C21H19NNaO3: 356.1263 [M+Na]+; found:
356.1255.
1-[6-(tert-Butyl)-4-(1H-indol-3-yl)-2-methyl-4H-chromen-3-yl]e-
1
thanone (3k): Brown liquid; H NMR (400 MHz, CDCl3, 258C, TMS):
Methyl 2-acetyl-5,5-bis(2-methyl-1H-indol-3-yl)pentanoate (7d):
Brown liquid; 1H NMR (400 MHz, CDCl3, 258C, TMS): d=1.88–1.96
(m, 2H), 2.08 (s, 3H), 2.20 (d, J=2.4 Hz, 6H), 2.36–2.43 (m, 2H),
3.45 (t, J=7.6 Hz, 1H), 3.64 (s, 3H), 4.38 (t, J=8.0 Hz, 1H), 6.95–
7.04 (m, 4H), 7.14 (d, J=8.0 Hz, 2H), 7.59 (dd, Ja =7.2, Jb =8.0 Hz,
2H), 7.74 ppm (s, 2H); 13C NMR (100 MHz, CDCl3): d=12.5, 12.5,
d=1.16 (s, 9H), 2.15 (s, 3H), 2.45 (s, 3H), 5.31 (s, 1H), 6.86 (d, J=
2.8 Hz, 1H), 6.93 (d, J=8.4 Hz, 1H), 7.10–7.13 (m, 3H), 7.19–7.22
(m, 1H), 7.32 (d, J=2.0 Hz, 1H), 7.75–7.77 (m, 1H), 8.34 ppm (s,
1H); 13C NMR (100 MHz, CDCl3): d=19.9, 29.4, 31.2, 33.5, 34.1,
111.3, 113.6, 115.6, 118.7, 119.5, 121.1, 121.9, 122.4, 124.4, 125.2,
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27.4, 28.7, 32.2, 34.7, 52.3, 59.7, 110.2, 113.8, 113.8, 118.9, 119.0,
119.1, 120.3, 128.0, 128.0, 130.9, 131.0, 135.0, 171.2, 203.4 ppm; IR:
n˜ =3396, 3055, 2951, 2866, 2248, 1736, 1709, 1617, 1550, 1487,
1459, 1358, 1301, 1245, 1154, 1046, 911, 741, 652, 591, 494,
430 cmÀ1; HRMS (ESI): m/z: calcd for C26H28N2NaO3: 439.1998
[M+Na]+; found: 439.1982.
119.4, 125.6, 128.0, 128.0, 128.7, 128.9, 129.1, 134.9, 143.1,
148.3 ppm; IR: n˜ =3090, 2953, 2924, 2855, 1714, 1455, 1346, 1219,
1080, 848, 818, 715, 578, 469 cmÀ1; HRMS (ESI): m/z: calcd for
C20H23N3Na: 328.1790 [M+Na]+; found: 328.1785.
Acknowledgements
3-[3,3-Bis(5-bromo-1H-indol-3-yl)propyl]pentane-2,4-dione (7g):
Brown liquid; 1H NMR (400 MHz, CDCl3, 258C, TMS): d=1.84–1.89
(m, 2H), 1.99–2.01 (m, 2H), 2.05 (s, 6H), 3.63 (t, J=7.2 Hz, 1H), 4.24
(t, J=7.2 Hz, 1H), 4.87 (s, 2H), 7.09 (s, 1H), 7.12–7.16 (m, 3H), 7.58
(s, 2H), 8.29 ppm (s, 2H); 13C NMR (100 MHz, CDCl3): d=21.0, 22.5,
26.7, 32.7, 33.8, 68.1, 112.2, 112.2, 112.8, 112.8, 118.0, 118.4, 121.5,
121.5, 122.7, 122.9, 124.5, 124.6, 128.2, 128.2, 135.1, 191.1,
204.8 ppm; IR n˜ =3417, 3075, 2250, 1722, 1696, 1560, 1457, 1358,
1247, 1099, 908, 796, 732, 587, 421 cmÀ1; HRMS (ESI): m/z: calcd for
C24H22Br2N2NaO2: 550.9946 [M+Na]+; found: 550.9933.
The authors would like to thank National Natural Science Foun-
dation of China for the financial support (21173089 and
21373093). The authors are also grateful for all the other staff
members in the Analytical and Testing Center of HUST. The
Program for new Century Excellent Talents in the University of
China (NCET-10–0383), Chutian Scholar Program of the Hubei
Provincial Government and the Cooperative Innovation Center
of Hubei Province are also acknowledged.
Ethyl 2-benzoyl-5,5-bis(5-bromo-1H-indol-3-yl)pentanoate (7i):
1
Brown liquid; H NMR (400 MHz, CDCl3, 258C, TMS): d=1.10 (t, J=
Keywords: acid catalysis · biomass · homogeneous catalysis ·
lignosulfonate · solid catalyst
7.2 Hz, 3H), 2.02 (s, 6H), 2.06–2.13 (m, 2H), 2.18–2.23 (m, 2H), 4.10
(q, Ja =6.8, Jb =14.0 Hz, 2H), 4.30–4.37 (m, 2H), 6.88 (s, 2H), 7.08–
7.16 (m, 4H), 7.37 (t, J=7.6 Hz, 2H), 7.50 (t, J=7.6 Hz, 1H), 7.59–
7.61 (m, 2H), 7.88 (d, J=7.6 Hz, 2H), 8.40 ppm (s, 2H); 13C NMR
(100 MHz, CDCl3): d=13.8, 27.6, 32.7, 33.8, 54.0, 61.5, 112.1, 112.7,
117.9, 118.1, 121.5, 121.6, 123.1, 123.1, 124.4, 128.2, 128.4, 128.6,
133.5, 135.2, 135.9, 170.0, 195.6 ppm; IR n˜ =3418, 3064, 2981,
2934, 2251, 1727, 1679, 1456, 1246, 1097, 1046, 909, 795, 732, 587,
421 cmÀ1; HRMS (ESI): m/z: calcd for C30H26Br2N2NaO3: 643.0208
[M+Na]+; found: 643.0198.
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Yellow solid; m.p: 71–738C; H NMR (400 MHz, CDCl3, 258C, TMS):
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J=6.8 Hz, 3H), 1.63 (sext, Ja =7.2, Jb =14.8, Jc =22.4 Hz, 2H), 2.58
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1
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Published online on December 4, 2013
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