Sulfonated Tetraphenylethylene-Based Hypercrosslinked Polymer as a Heterogeneous Catalyst for the Synthesis of Symmetrical Triarylmethanes via a Dual C-C Bond-Cleaving Path

Article abstract of DOI:10.1055/a-1277-3995

A sulfonic acid functionalized tetraphenylethylene-based hypercrosslinked polymer (THP-SO ₃H) with a well-developed porous network and accessible sulfonic acid sites was synthesized and characterized by different analytical techniques. The cata

Full text of DOI:10.1055/a-1277-3995

Submission Date:
Accepted Date:
Publication Date:
2020-07-12
2020-10-01
2020-10-01
Accepted Manuscript
Synlett
Sulfonated Tetraphenylethylene-Based Hypercrosslinked Polymer as a Hetero-
geneous Catalyst for the Synthesis of Symmetrical Triarylmethanes via a Dual
C–C Bond Cleaving Path
Gitumoni Kalita, Namrata Deka, Dipankar Paul, Loknath Thapa, Gitish K Dutta, Paresh N Chatterjee.
Affiliations below.
DOI: 10.1055/a-1277-3995
Please cite this article as: Kalita G, Deka N, Paul D et al. Sulfonated Tetraphenylethylene-Based Hypercrosslinked Polymer as a Hetero-
geneous Catalyst for the Synthesis of Symmetrical Triarylmethanes via a Dual C–C Bond Cleaving Path. Synlett 2020. doi: 10.1055/a-
1277-3995
Conflict of Interest: The authors declare that they have no conflict of interest.
This study was supported by Science and Engineering Research Board (http://dx.doi.org/10.13039/501100001843), SB/FT/CS-
075/2014,SB/FT/CS-115/2014
Abstract:
A sulfonic acid functionalized tetraphenylethylene-based hypercrosslinked polymer (THP-SO3H) with a well-developed porous
network and accessible sulfonic acid sites was synthesized and characterized by different analytical techniques. The catalytic
prowess of the synthesized material THP-SO3H was investigated in a challenging dual C–C bond-breaking reaction for the syn-
thesis of symmetrical triarylmethanes (TRAMs) in high yield. The scope of the developed metal-free method was also explored
with a wide variety of substrates. The organocatalyst can be easily recovered by filtration and reused up to five consecutive
cycles without substantial loss in its catalytic efficacy.
Corresponding Author:
Paresh N Chatterjee, National Institute of Technology Meghalaya, Chemistry, Bijni Complex, 793003 Shillong, India, paresh.chatterjee@
nitm.ac.in
Affiliations:
Gitumoni Kalita, National Institute of Technology Meghalaya, Chemistry, Shillong, India
Namrata Deka, National Institute of Technology Meghalaya, Chemistry, Shillong, India
Dipankar Paul, National Institute of Technology Meghalaya, Chemistry, Shillong, India
[…]
Paresh N Chatterjee, National Institute of Technology Meghalaya, Chemistry, Shillong, India
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Synlett
Letter
Sulfonated Tetraphenylethylene-Based Hypercrosslinked Polymer as a
Heterogeneous Catalyst for the Synthesis of Symmetrical
Triarylmethanes via a Dual C–C Bond Cleaving Path
Gitumoni Kalita†
Namrata Deka†
Dipankar Paul†
Loknath Thapa
Gitish K. Dutta*
Paresh Nath Chatterjee*
Department of Chemistry, National Institute of Technology
Meghalaya, Bijni Complex, Laitumkhrah, Shillong 793003,
Meghalaya, INDIA
† Equal contribution
* indicates the main/corresponding author.
paresh.chatterjee@nitm.ac.in
gitish.dutta@nitm.ac.in
Click here to insert a dedication.
Received:
Accepted:
hydrophilic environment. In this regard, the effective design of
Published online:
DOI:
hypercrosslinked polymer-based catalysts may help to combine
the advantages of both heterogeneous and homogeneous
Abstract
A
sulfonic acid functionalized tetraphenylethylene-based
catalysts. Acid-functionalized hypercrosslinked polymers have
been recently utilized as heterogeneous catalysts, mostly for the
conversion of biomass to biofuel,6 biofuel additives7 and
hydroxymethylfurfural (HMF).8 Bhaumik and his group have
hypercrosslinked polymer (THP-SO3H) with a well-developed porous network
and accessible sulfonic acid sites was synthesized and characterized by
different analytical techniques. The catalytic prowess of the synthesized
material THP-SO3H was investigated in a challenging dual C–C bond-breaking
reaction for the synthesis of symmetrical triarylmethanes (TRAMs) in high
yield. The scope of the developed metal-free method was also explored with
a wide variety of substrates. The organocatalyst can be easily recovered by
filtration and reused up to five consecutive cycles without substantial loss in
its catalytic efficacy.
recently employed
a hypercrosslinked supermicroporous
polymer as a heterogeneous catalyst for synthesizing biodiesel.6
However, the scope of such functionalized polymer-based
catalysts has not been investigated much in other organic
synthetic applications.
Keywords hypercrosslinked polymer, heterogeneous catalyst, reusable, C–C
bond-breaking, triarylmethane.
For example, organic reactions proceeding through
unusual yet challenging C–C bond-breaking reactions still await
the same level of interest as C–C bond-forming counterparts.
Over the past years, several catalytic routes for the cleavage of
the C–C bonds have been developed by researchers.11 Our
interest on exploring new catalytic approaches for the activation
of C–C bonds, lead us to develop a facile FeCl3 catalyzed dual C–C
bond-breaking reaction in homogeneous medium for the
synthesis of symmetrical and unsymmetrical triarylmethanes
(TRAMs).12 Inspite of tremendous reactivity and selectivity of
homogeneous catalysts, it has limited applications in industrial
processes due to the difficulties associated with the removal,
recovery, and recycling of the active catalysts. Till date, several
methods are reported in the literature on the synthesis of
TRAMs.13 To the best of our knowledge, the synthesis of TRAMs
Functionalization of porous organic polymers has
provided an exciting platform for catering to a varied array of
applications such as adsorption, energy applications, catalysis,
etc.1 The high thermal and chemical stability, high specific
surface areas and hierarchical pore networks of porous organic
polymers have attracted significant attention over recent
decades.2 Moreover, they have an added advantage of the ease of
preparation and functionalization using mild synthetic
conditions. The proper selection of monomer units further aids
in designing polymer materials with tailor-made properties for
different applications. Based on the reactions involved in the
synthetic process, porous organic polymers may be further
classified into the categories such as hypercrosslinked
polymers, microporous organic polymers, covalent organic
framework, etc.3 Hypercrosslinked polymers possessing high
surface areas, inherent porosity, good chemical and thermal
stability and a rigid skeleton for easy incorporation of catalytic
sites have been proven to be a promising candidate for their use
as heterogeneous catalysts.4 Heterogeneous catalysts are being
gradually preferred over classical homogeneous catalysts owing
to their non-corrosiveness, ease of recovery and reusability.5
However, common limitations of heterogeneous catalysts
via
a dual C–C bond-breaking reaction of diarylmethyl
substituted 1,3-dicarbonyl derivatives 1 has not been attempted
with heterogeneous catalysts. In this regard, acid-functionalized
hypercrosslinked polymers can be used as reusable
heterogeneous catalyst for the synthesis of TRAMs. Here, we
have
synthesized
a
sulfonic
acid
functionalized
hypercrosslinked polymer derived from tetraphenylethylene
(TPE). Hypercrosslinked polymers have been previously used
by researchers as polymeric supports due to their porous
natures and high thermal stabilities.14 However, the choice of
monomer units heavily influences the physico-chemical
include high cost, low yields and catalyst poisoning in
a
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Synlett
Letter
characteristics of the polymer. The tetraphenylethylene (TPE)
moiety consists of peripheral phenyl rings, which prevents the
π-π stacking of its polymerized form. Hence, the surface area of
TPE-based hypercrosslinked polymers is usually very high and
provides a suitable platform for the incorporation of numerous
catalytic sites. Moreover, increasing the crosslinking between
the monomer units improves the thermal stability of the
bond cleavage in the reaction. It is noteworthy that the use of 96
mg catalyst at 80 °C produced the maximum yield of the product
3a in 30 min (Table 1, entry 3). An increase in the amount of
catalyst loading (144 mg) did not affect the yield of the reaction
significantly (Table 1, entry 8). But a lower catalyst loading (48
mg) resulted in the lesser yield of the product 3a (Table 1, entry
9). Besides, no dual C–C bond-breaking reaction was noticed in
the absence of catalyst and the starting materials were
recovered quantitatively (Table 1, entry 10). It is to be noted
that the leaving 1,3-diphenylpropan-1,3-dione and 1,3,5-
trimethoxybenzene were isolated in more than 90% yields
(Table 1, entry 3).
polymeric
catalyst.
The
synthesized
TPE-based
hypercrosslinked polymer (THP) has a high surface area and
optimum pore dimensions, which make it a suitable framework
for introducing sulfonic acid sites. The sulfonated polymer
(THP-SO3H) possesses high sulfonic acid content and good
thermal stability. Also, THP-SO3H shows high potential as a
heterogeneous catalyst for the synthesis of symmetrical TRAMs
Table 1: Optimization of reaction conditionsa
via
a dual C–C bond-breaking reaction of diarylmethyl
substituted 1,3-dicarbonyl derivatives 1. It is noteworthy to
mention that, TRAM skeleton is found in several natural
products, pharmaceuticals, dyes etc.15 Moreover, the application
of THP-SO3H as a reusable heterogeneous catalyst in the dual C–
C bond-breaking reaction enhances the practical utility of the
present work.
The tetraphenylethylene-based hypercrosslinked
polymer (THP) scaffold was synthesized via a simple Friedel–
Crafts based crosslinking reaction with tetraphenylethylene as
the monomer and formaldehyde dimethylacetal as the
crosslinker.16 Sulfonation of the polymer was successfully
carried out in chlorosulfonic acid (ClSO3H) at 25 °C under N2
atmosphere (Scheme S1 of ESI).6 The details of the structural
and morphological characterizations of THP-SO3H are included
in the ESI.
Entry
1
Solvent
MeNO2
MeCN
DCE
Temp. (°C)
Time (min)
Yield (%)b
89
80
80
80
80
80
55
RT
80
80
80
45
60
2
81
3
30
94
4
toluene
EtOH
DCE
90
64
5
180
180
300
30
56
6
78
7
DCE
52
8c
9d
10e
DCE
96
DCE
30
78
DCE
60
nil
aReaction conditions: 1a (480 mg,1.0 mmol), 2a (246 mg, 3.0 mmol), catalyst (96
mg), solvent (2 mL); Isolated yields; catalyst (144 mg); catalyst (48 mg); No
catalyst.
After characterizing the THP-SO3H material, we were
interested to explore its catalytic prowess for the synthesis of
symmetrical TRAMs via a challenging dual C–C bond-cleaving
reaction of diarylmethyl substituted 1,3-dicarbonyl derivatives
1 in a heterogeneous medium. To investigate the optimized
reaction conditions, we chose 1,3-diphenyl-2-(phenyl(2,4,6-
trimethoxyphenyl)methyl)propane-1,3-dione (1a) and 2-
methylfuran (2a) as the model substrates for the synthesis of
b
c
d
e
After optimizing the reaction conditions, we explored
the substrate scope of the developed method with our in-house
synthesized organocatalyst THP-SO3H. From our previous work,
we experienced that the combination of 1,3-diphenylpropan-
1,3-dione (as the 1,3,-dicarbonyl substituent) and 2,4,6-
trimetheoxyphenyl unit (as the electron-rich arene substituent)
in the starting substrates 1 showed the best results during dual
C–C bond-breaking reaction.12
symmetrical TRAM 3a by the cleavage of both Csp3–Csp3 and Csp3
–
Csp2 bonds in substrate 1a (Table 1). Initially, we screened
different solvents (Table 1, entries 1–5) for the dual C–C bond
cleavage in the presence of THP-SO3H to find out the suitable
solvent for the reaction. Among different solvents, the highest
yield of the symmetrical TRAM 3a was obtained in DCE solvent
using the synthesized organocatalyst at 80 °C in 30 min (Table
1, entry 3). The reaction gave comparably lower yield of the
desired TRAM 3a in MeNO2, MeCN and toluene solvents (Table
1, entries 1–2, 4). However, polar protic solvent, such as EtOH
gave poor yield of 3a even after 3 h (Table 1, entry 5). The
temperature also played a significant role in the dual C–C bond-
breaking reaction. When we decreased the temperature from 80
°C to 55 °C, only 78% yield of desired product 3a was obtained
after 3 h (Table 1, entry 6). Further decreasing the temperature
to room temperature, product 3a was obtained only in 52%
yield after 5 h (Table 1, entry 7). Unlike our previous report,12
we did not isolate any unsymmetrical TRAM via the cleavage of
Csp3–Csp3 bond only,17 resulting dibenzoylmethane as the carbon-
based leaving group. In addition, we varied the catalyst loading
to determine the optimum amount of THP-SO3H for the dual C–C
Figure 1: List of nucleophiles used in the dual C–C bond cleavage reaction.
Hence, to study the catalytic efficacy of THP-SO3H for
the synthesis of symmetrical TRAMs, we varied only the R-
group in 1, keeping 1,3-diphenylpropan-1,3-dione and 2,4,6-
trimetheoxyphenyl units intact in the precursor 1 (Scheme 1).
We found that the aromatic ring bearing EWG, in substrate 1
generated slightly higher yields of the symmetrical TRAMs 3b-d
than the aromatic ring bearing EDG 3e-f.
A heteroaryl
substituent in substrate 1g provided the corresponding product
3g in 71% yield. Furthermore, the reaction performed well
when 2,5-dimethylfuran (2b) was used as nucleophile
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producing the desired TRAM 3h in good yield. Then, we
examined other nucleophiles based on their performance in
dual C–C bond-cleaving reaction. In the presence of indole
derivatives (2c-i), the corresponding bis-indolylmethanes (3i-o)
were obtained in good yield. Surprisingly, 5-methoxyindole (2g)
gave a lower yield of the desired bis-indolylmethane derivative
3m after prolonged reaction time. The N-substituted indoles 2h-
In view of commercial applications, we also explored
the potential for reusability of the synthesized organocatalyst
THP-SO3H in the dual C–C bond-breaking reaction of substrate
1a and 2a. After 30 min of the reaction time in each cycle, the
catalyst was recovered by filtration, washed with DCE and dried
at 100 °C under vacuum oven for 3 h (the detailed procedure is
given in ESI). The recovered catalyst was reused for four
consecutive cycles without significant loss in its catalytic
efficiency (Figure 2).
The FT-IR spectrum of the reused catalyst after the
fifth cycle shows the same pattern as the synthesized THP-SO3H
material (Figure S7 of ESI), which indicates that the active site of
the heterogeneous catalyst remains intact even after the fifth
cycle.
i
were effective in the dual C–C bond-cleaving reaction
generating the symmetrical TRAMs 3n-o in excellent yields. 2-
Methylthiophene (2j) also reacted well with substrate 1a to give
the symmetrical TRAM 3p in 79% yield. It is important to note
that 4-methoxythiophenol (2k) took part in the reaction
producing 55% yield of the product 3q with two new Csp3–S
bonds at the cost of two C–C bonds. While examining the scope
of nucleophiles, we noticed that the symmetrical TRAM did not
form during the reactions between substrate 1a and
nucleophiles 2l-n via the dual C–C bond-breaking reaction.
Instead, we isolated unsymmetrical TRAMs 4 due to the
exclusive Csp3–Csp3 bond-cleaving reaction of 1a in the presence
of the above mentioned nucleophiles. We previously noted the
similar observations in our FeCl3 catalyzed dual C–C bond-
breaking work.12 These results indicate that the Csp3–Csp3 bond is
relatively easier to cleave than Csp3–Csp2 bond in substrate 1 in
our developed reaction conditions.18
Figure 2: Recyclability of THP-SO3H catalyst in the dual C–C bond-breaking
reaction.
Based on the above observations and the related
literature about the dual C–C bond-breaking reaction, we
propose
a plausible reaction mechanism for the reaction
between substrate 1a and 2a in the scheme 2. THP-SO3H has
abundant acidic sites due to the presence of a large number of -
SO3H groups at the surface of the hypercrosslinked polymer and
provides ample H+ ion in the reaction medium. The reaction may
be initiated by the activation of carbonyl groups of the starting
material 1a in the presence of H+ to produce a species A.12 2-
Methylfuran (2a) combines with the electrophilic species Aʹ to
form unsymmetrical TRAM B and consequently releases 1,3-
diphenylpropan-1,3-dione by the cleavage of Csp3–Csp3 bond. The
electron-donating –OMe group of the species B undergoes
conjugation and gets protonated in the acidic medium to
generate an ionic species C which may decompose to species D
via the elimination of 1,3,5-trimethoxybenzene.19 Subsequently,
a second molecule of 2a reacts with the electrophilic center in
species D to produce the desired symmetrical TRAM 3a via a
Csp3–Csp2 bond-breaking reaction and a proton is consequently
released in the reaction medium.
In conclusion, we have synthesized a novel sulfonic
acid functionalized tetraphenylethylene-based hypercrosslinked
polymer (THP-SO3H) with a porous network and accessible
sulfonic acid sites. Due to the abundant accessible acidic sites in
the material, its catalytic property was examined on a dual C–C
bond-breaking reaction in diarylmethyl substituted 1,3-
dicarbonyl derivatives. THP-SO3H showed promising catalytic
activity in the synthesis of symmetrical TRAMs via the cleavage
of both Csp3–Csp3 and Csp3–Csp2 bonds in mild reaction
conditions.20 The generality of the reaction was explored on a
Scheme 1: Substrate scope of the C–C bond-breaking reaction for the
synthesis of TRAMs. Reaction conditions for 3a-h: 1 (1.0 mmol), 2a (3.0
mmol), THP-SO3H (96 mg), DCE (2 mL), temperature 80 °C. Reaction
conditions for 3i-q and 4a-c: 1 (1.0 mmol), 2 (2.0 mmol), THP-SO3H (96 mg),
DCE (2 mL), temperature 80 °C.
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(5) Davies, I. W.; Matty, L.; Hughes, D. L.; Reider, P. J. J. Am. Chem. Soc.
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R.; Choi, B.; Madrahimov, S. T.; Nguyen, S. T. ACS Sustain. Chem. Eng.
2019, 7, 8126.
diverse range of substrates and the desired product was
obtained in high yield. Due to its heterogeneity in the reaction
medium, the catalyst could be recycled for further use. The
catalyst was reused up to five reaction cycles without any
substantial decrease in its catalytic efficiency. The results
described here demonstrate the first-ever synthesis of
symmetrical TRAMs via a metal-free, dual C–C bond-breaking
strategy
using
sulfonated
tetraphenylethylene-based
(11) (a) Yao, X.; Li, C. J. J. Org. Chem. 2005, 70, 5752. (b) Li, H.; Li, W.;
Liu, W.; He, Z.; Li, Z. Angew. Chem. Int. Ed. 2011, 50, 2975. (c) Mahoney,
S. J.; Lou, T.; Bondarenko, G.; Fillion, E. Org. Lett. 2012, 14, 3474.(d)
Armstrong, E. L.; Grover, H. K.; Kerr, M. A. J. Org. Chem. 2013, 78,
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11776. (f) Yao, Q.; Kong, L.; Wang, M.; Yuan, Y.; Sun, R.; Li, Y. Org. Lett.
2018, 20, 1744. (g) Yao, Q.; Kong, L.; Zhang, F.; Tao, X; Li, Y. Adv. Synth.
Catal. 2017, 359, 3079. (h) Cheng, X.; Zhou, Y.; Zhnag, F.; Zhu, K.; Liu,
Y.; Li, Y. Chem. Eur. J. 2016, 22, 12655. (i) Zhou, Y.; Tao, X.; Yao, Q.;
Zhao, Y.; Li, Y. Chem. Eur. J. 2016, 22, 17936.
hypercrosslinked polymer as a heterogeneous catalyst.
(12) Paul, D.; Khatua, S.; Chatterjee, P. N. New J. Chem. 2019, 43, 10056.
(13) (a) Esquivias, J.; Gomez Arrayas, R.; Carretero, J. C. Angew. Chem.
Int. Ed. 2006, 45,629. (b) Mondal, S.; Panda, G. RSC Adv. 2014, 4,
28317. (c) Yue, C.; Na, F.; Fang, X.; Cao, Y.; Antilla, J. C. Angew. Chem. Int.
Ed. 2018, 57, 11004. (d) Zhang, Z.; Wang, H.; Qiu, N.; Kong, Y.; Zeng, W.;
Zhang, Y.; Zhao, J. J. Org. Chem. 2018, 83, 8710.
(14) Lee, J. -S. M.; Briggs, M. E.; Hasell, T.; Copper, A. I. Adv. Mater.
2016, 28, 9804.
(15) (a) Nambo, M.; Crudden, C. M. ACS Catal. 2015, 5, 4734. (b)
Praveen, P. J.; Parameswaran, P. S.; Majik, M. S. Synthesis 2015, 47,
1827. (c) Shiri, M.; Zolfigol, M. A.; Kruger, H. G.; Tanbakouchian, Z.
Chem. Rev. 2010, 110, 2250.
(16) Zeng, J. H.; Wang, Y. F.; Gou, S. Q.; Zhang, L. P.; Chen, Y.; Jiang, J. X.;
Shi, F. ACS Appl. Mater. Interfaces 2017, 9, 34783.
(17) The following unsymmetrical TRAM (via only Csp3–Csp3 bond
cleavage) was not isolated in the reaction.
Scheme 2: Plausible reaction mechanism for the reaction between 1a and 2a
catalyzed by THP-SO3H.
Funding Information
SERB is gratefully acknowledged for financial support to G. K. D. (grant
no. SB/FT/CS-075/2014) and P. N. C. (grant no. SB/FT/CS-115/2014).
Acknowledgment
(18). Luo, Y. -R.; Kerr, J. CRC Handbook of Chemistry and Physics 2012,
89, 89.
(19). (a) Thirupathi, P.; Soo Kim, S. J. Org. Chem. 2010, 75, 5240. (b)
Castellani, C. B.; Perotti, A.; Scrivanti, M.; Vidari, G. Tetrahedron 2000,
56, 8161.
We thank NIT Meghalaya for financial support to G. K., N. D. and D. P.
SAIF, NEHU; NMR Research Centre, IISc Bangalore; SAIC, TU; Centre for
Energy, IIT Guwahati; MSE, IIT Kanpur and SAIF, IIT Bombay are also
acknowledged for analytical facilities.
(20). Typical procedure for the synthesis of 3a
A 25 mL round-bottom flask equipped with a magnetic bar and water
condenser were charged with 1a (1.0 mmol), 2a (3.0 mmol), DCE (2.0
mL) and THP-SO3H (96 mg) in an air atmosphere. The flask was placed
in a constant temperature oil-bath at 80 °C and the progress of the
reaction was monitored by TLC. After 30 min, the mixture was filtered
to separate the catalyst and washed twice with DCE (2 x 5 mL). Then
the filtrate was removed under reduced pressure and the crude
product was purified by dry columnvacuum chromatography (silica
gel G, petroleum ether 60-80 °C/EtOAc) to give a yellow oily liquid;
yield: 94%.
1H NMR (400 MHz, CDCl3): δ (ppm) 2.158 (s, 6H), 5.256 (s, 1H), 5.788
(d, J = 3.2 Hz, 4H), 7.159–7.243 (m, 5H). 13C NMR (100 MHz, CDCl3): δ
(ppm) 13.65, 45.12, 106.08, 108.19, 126.97, 128.40, 128.44, 140.00,
151.46, 152.85.
Supporting Information
YES (this text will be updated with links prior to publication)
References and Notes
(1) (a) Guillerm, V.; Weseliński, Ł. J.; Alkordi, M.; Mohideen, M. I. H.;
Belmabkhout, Y.; Cairns, A. J.; Eddaoudi, M. Chem. Commun. 2014, 50,
1937. (b) Hao, S.; Liu, Y.; Shang, C.; Liang, Z.; Yu, J. Polym. Chem. 2017,
8, 1833. (c) Dawson, R.; Cooper, A. I.; Adams, D. J. Polym. Int. 2013, 62,
345.
(2) Zhang, Y.; Riduan, S. N. Chem. Soc. Rev. 2012, 41, 2083.
(3) Ahmed, D. S.; El-Hiti, G. A.; Yousif, E.; Ali, A. A.; Hameed, A. S. J.
Polym. Res. 2018, 25, 75.
(4) Huang, J.; Turner, S. R. Polym. Rev. 2018, 58, 1.
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Sulfonated Tetraphenylethylene-Based Hypercrosslinked Polymer as a Heterogeneous
Catalyst for the Synthesis of Symmetrical Triarylmethanes via a Dual C–C Bond Cleaving
Path
Gitumoni Kalita,† Namrata Deka,† Dipankar Paul,† Loknath Thapa, Gitish K. Dutta,* Paresh
Nath Chatterjee*
Department of Chemistry, National Institute of Technology Meghalaya, Bijni Complex,
Laitumkhrah, Shillong 793003, Meghalaya, INDIA
† Equal contribution
* Corresponding author
Email of corresponding authors: paresh.chatterjee@nitm.ac.in
gitish.dutta@nitm.ac.in
Supplementary Material
Contents
Page
2
1
2
3
4
5
6
7
8
9
General remarks
Synthesis of sulfonated THP (THP-SO3H)
3
Characterization of THP-SO3H material
3-6
7
Calculation of acid strength of THP-SO3H material
General procedure for the optimization of reaction conditions
General procedure for the synthesis of TRAMs 3a-g
General procedure for the synthesis of TRAMs 3h-q and 4
General procedure for recyclability of the catalyst THP-SO3H
FT-IR spectra of THP-SO3H material after the fifth cycle
7-8
8
8
8
9
10 Analytical data of products 3 and 4
9-14
15
16-35
11 References
12 1H and 13C NMR spectra of products 3 and 4
1

1. General remarks
All reagents and solvents are of analytical reagent (AR) grade and were procured from SRL,
Spectrochem, Merck, and Alfa Aesar. Solvents were distilled prior to use. All the reactions were
done in oven-dried glass apparatus in an air atmosphere unless otherwise mentioned. Progress of
the reactions was monitored by TLC on silica gel 60 F254 using UV light and p-anisaldehyde stain
as visualizing agents. All the organic products were purified by dry column vacuum
chromatography using silica gel G as the stationary phase and petroleum ether 60-80 °C/ethyl
1
acetate as the eluent. H and 13C NMR spectra of synthesized TRAMs were measured on a
BrukerAvance II (1H NMR: 400 MHz and 13C NMR: 100 MHz) spectrometer. Chemical shifts are
reported in ppm from TMS, with the solvent resonance as the internal standard (unless otherwise
mentioned, chloroform: δ 7.26 ppm). Data are reported as follows: chemical shifts, multiplicity
(s=singlet, d=doublet, t=triplet, q=quartet, br=broad, dd=double doublet, m=multiplet), coupling
constant (in Hz), integration. 13C NMR spectra were recorded at 100 MHz with proton decoupling.
Chemical shifts are reported in ppm from TMS with the solvent resonance as the internal standard
(unless otherwise mentioned, chloroform: δ 77.0 ppm). Elemental analyses were carried out using
a FlashEA 1112 elemental analyzer. Fourier transform infrared (FT-IR) spectra of THP and THP-
SO3H were recorded using PerkinElmer Spectrum Two spectrometer. The surface areas of the
polymers were calculated from nitrogen adsorption-desorption isotherms measured using
QuantachromeAutosorbiQ. The pore-size distributions were calculated based on NLDFT
calculations using a trial version of SAIEUS software. Thermogravimetric analyses (TGA) were
conducted in an inert atmosphere at a heating rate of 10 °C min-1. The solid-state 13C NMR
spectrum of THP-SO3H was obtained on a 400 MHz JEOL ECX400. Field emission scanning
electron microscopy (FESEM) analysis was done with NOVA NANOSEM 450 instrument to
analyze the surface morphologies. Tetraphenylethylene-based hypercrosslinked polymer (THP)
was synthesized by following a previously reported procedure in the literature.1 The various
precursors 1 for the synthesis of TRAMs were also prepared by following a previously reported
procedure.2-3
2

2. Synthesis of sulfonated THP (THP-SO3H)
Scheme S1: Synthesis of sulfonic acid functionalized tetraphenylethylene-based hypercrosslinked
polymer (THP-SO3H).
Vacuum-dried THP (500 mg) was taken in a two-necked round-bottom flask with 15 mL of
degassed anhydrous DCM under N2 atmosphere. After the mixture was cooled to 0 °C in an ice
bath, 12 mL of chlorosulfonic acid (ClSO3H) was added drop-wise from a dropping funnel with
constant stirring. The mixture was further stirred at 25 °C for 2 days under N2 atmosphere. The
reaction mixture was quenched with ice, and the precipitate was filtered. The obtained precipitate
was washed several times with double distilled water and acetone. Finally the product THP-SO3H
was vacuum dried at 80 ºC for 24 h.
3. Characterization of THP-SO3H material
The structure and morphology of the sulfonated hypercrosslinked polymer (THP-SO3H) were
characterized using different analytical techniques. The amount of sulfonic acid (-SO3H) sites
present in the material was quantitatively analyzed by a back-titration method. THP-SO3H material
was found to contain 11.11 mmol/g acidity. The facile preparation and high scalability of the
sulfonated polymer stress on the viability of the material for practical applications. FT-IR and
solid-state 13C NMR spectra (Figure S1 & S2) confirm the formation of the polymeric framework
of THP-SO3H. The band at ~620 cm−1 may be assigned to the stretching vibration of C‒S bond
present in the material4 and thus confirms the successful anchoring of the –SO3H group to the
hypercrosslinked polymer (Figure S1). The bands at ~1050 cm−1and ~1180 cm−1 are due to the
O=S=O group.5 The band at ~2960 cm−1 is attributed to the presence of unsaturated C‒H
framework (C=C–H). The presence of O‒H group was confirmed by a broad hump centered
13
around 3400 cm−1. In the C CP-MAS NMR spectra (Figure S2), a strong peak appears at 129
ppm, which may be attributed to the presence of the phenyl ring carbon in the crosslinked
framework. A hump at a slightly higher value (139 ppm) of the spectrum was recognized for the
successful sulfonation of the phenyl ring in the polymer. The sulfonation of the precursor, THP,
was also confirmed by analyzing the elemental contents of the polymer before and after the
sulfonation step (Table S1). The thermal stability of the polymers was investigated using
3

thermogravimetric analysis (TGA) (Figure S3). Both THP and THP-SO3H possess high thermal
stability at temperatures up to 700 °C. THP undergoes a minor weight loss of 2.3 % till 300 °C,
beyond which thermal degradation of C‒H and C‒C bonds takes place leading to a decrease in the
thermogram.6 The thermal decomposition of the sulfonated polymer, THP-SO3H occurs at a lower
temperature than its precursor polymer, which may be due to the desulfonation of acid groups at a
temperature of around 200 °C.7 Moreover, 4% weight loss can be observed up to 100 °C in the
thermogram of THP-SO3H because of the evaporation of absorbed water molecules in the sulfonic
acid sites. Nevertheless, retention of a high carbon mass percentage of THP-SO3H even at a high
temperature of 700 °C suggests good thermal stability of the polymer. FESEM images of THP-
SO3H reveal the presence of aggregated clusters of irregular particles (Figure S4). The FESEM
images obtained are typically observed in organic polymers with a highly porous framework.8
High surface area and accessible pores in a polymer are beneficial for the incorporation of sulfonic
acid groups. The N2 adsorption-desorption isotherms of THP polymer is shown in Figure S5. The
N2 isotherm displays a small knee at low relative pressure, which could be attributed to the
presence of some micropores present.9 However, the hysteresis loop in the type IV isotherm
indicates towards the phenomena of capillary condensation occurring in the mesopores.10 The BET
surface area of the THP polymer, calculated from the multi-point BET method is 995 m2g−1. The
porosity profile of THP was also investigated with the help of a pore-size distribution plot (Figure
S6). The presence of both micropores and mesopores in the material provides a suitable platform
for introducing accessible sulfonic acid sites.
Figure S1: FT-IR spectrum of THP and THP-SO3H materials.
4

Figure S2:13C CP-MAS NMR spectrum THP-SO3H material. Spinning side bands are denoted
by asterisk (*) symbols.
Table S1: Elemental content obtained from CHNS analysis
Sample
THP
C (%)
73.9
H (%)
4.4
O (%)
21.7
S (%)
-
THP-SO3H
63.0
4.7
23.8
8.5
Oxygen content was calculated by subtracting the total elemental content from 100%.
Figure S3: TGA plots of THP and THP-SO3H materials.
5

Figure S4: FESEM images of THP-SO3H material at a) 25000X and b) 150000X magnifications.
Figure S5: N2 adsorption-desorption isotherm of the precursor, THP material.
Figure S6: Pore-size distribution plot of the precursor, THP material.
4. Calculation of acid strength of THP-SO3H material 11
6

A 100 mL round-bottom flask equipped with a magnetic bar was charged with the sulfonated
material THP-SO3H (100 mg) and 50 mL water. The flask was placed in constant temperature oil-
bath at 40 °C. The mixture was stirred for 8 h at 40 °C. After 8 h, the mixture was cooled to room
temperature. 10 mL aqueous mixture of THP-SO3H was taken in a 100 mL conical flask and 10
mL NaOH solution of strength 0.02894 (N) was added to it and allowed to stir for overnight. After
filtration, the excess NaOH solution was back titrated with 0.112 (N) oxalic acid solution. 0.6 mL
of oxalic acid solution was consumed to reach the first equivalence point of oxalic acid.
The amount of acid per 1 g of the THP-SO3H was calculated by the following method:
V(NaOH) x S(NaOH) = V(OX) x S(OX)
V(NaOH) x 0.02894 = 0.6 x 0.112
V(NaOH) = 2.322 mL
So, the NaOH required to neutralize the acidic site of the THP-SO3H = (10-2.322) mL = 7.678
mL.
V(NaOH) x S(NaOH) =V(THP-SO3H) x S(THP-SO3H)
7.678 x 0.02894= 10 x S(THP-SO3H)
S(THP-SO3H) = 0.02222 (N)
The equivalent weight of -SO3H group = 81.
Calculation:
1000 mL 1 (N) THP-SO3H = 81 g free –SO3H group in the sulfonated material (THP-SO3H)
Therefore, 50 mL 0.02222 (N) THP-SO3H = 0.089991 g free –SO3H group
=1.111 mmol free –SO3H group
So, 50 mL 0.02222 (N) THP-SO3H aqueous mixture contains 0.089991 g free –SO3H site
i.e. 100 mg of THP-SO3H sample contains 1.111 mmol free –SO3H site
Therefore, 1000 mg of THP-SO3H sample contains 11.11 mmol free –SO3H site.
5. General procedure for the optimization of reaction conditions
A 25 mL round-bottom flask equipped with a magnetic bar and water condenser were charged
with substrates 1a (480 mg, 1.0 mmol), 2a (246 mg, 3.0 mmol), solvent (2.0 mL) and THP-SO3H
(96 mg) in air atmosphere. The flask was placed in a constant temperature oil-bath at 80 °C, and
the progress of the reaction was monitored by TLC. After the specified time as mentioned in Table
1 of the manuscript, the solvent was removed under reduced pressure and the crude product was
purified by dry column vacuum chromatography (silica gel G, petroleum ether 60-80 °C/EtOAc).
7

6. General procedure for the synthesis of TRAMs 3a-g
A 25 mL round-bottom flask equipped with a magnetic bar and water condenser were charged
with 1 (1.0 mmol), 2a (3.0 mmol), DCE (2.0 mL) and THP-SO3H (96 mg) in an air atmosphere.
The flask was placed in a constant temperature oil-bath at 80 °C and the progress of the reaction
was monitored by TLC. After the specified time as mentioned in Scheme 1 of the manuscript, the
mixture was filtered to separate the catalyst and washed twice with DCE (2 x 5 mL). Then the
filtrate was removed under reduced pressure and the crude product was purified by dry column
vacuum chromatography (silica gel G, petroleum ether 60-80 °C/EtOAc) to obtain the desired
product.
7. General procedure for the synthesis of TRAMs 3h-q and 4
A 25 mL round-bottom flask equipped with a magnetic bar and water condenser were charged
with 1 (1.0 mmol), 2 (2.0 mmol), DCE (2.0 mL) and THP-SO3H (96 mg) in an air atmosphere.
The flask was placed in a constant temperature oil-bath at 80 °C and the progress of the reaction
was monitored by TLC. After the specified time as mentioned in Scheme 1 of the manuscript, the
mixture was filtered to separate the catalyst and washed twice with DCE (2 x 5 mL). Then the
filtrate was removed under reduced pressure and the crude product was purified by dry column
vacuum chromatography (silica gel G, petroleum ether 60-80 °C/EtOAc) to obtain the desired
product.
8. General procedure for recyclability of the catalyst THP-SO3H
A 25 mL round-bottom flask equipped with a magnetic bar and water condenser were charged
with 1a (1.0 mmol), 2a (3.0 mmol), DCE (2.0 mL) and TMOP-SO3H (96 mg) in an air atmosphere.
The flask was placed in a constant temperature oil-bath at 80 °C and the progress of the reaction
was monitored by TLC. After 30 min, the catalyst was recovered by simple filtration, washed twice
with DCE and dried at 100 °C under vacuum oven for 3 h. Then the recovered catalyst was used
for further four cycles. The crude product was purified after each cycle to get the isolated yield.
8

9. FT-IR spectra of THP-SO3H material after the fifth cycle.
Figure S7: FT-IR spectra of THP-SO3H material after the fifth cycle.
10. Analytical data of products 3 and 4
Me
O
O
Me
5,5'-(Phenylmethylene)bis(2-methylfuran) (3a):3 Yellow oily liquid. 1H NMR (400 MHz, CDCl3):
δ (ppm) 2.158 (s, 6H), 5.256 (s, 1H), 5.788 (d, J = 3.2 Hz, 4H), 7.159–7.243 (m, 5H). 13C NMR
(100 MHz, CDCl3): δ (ppm) 13.65, 45.12, 106.08, 108.19, 126.97, 128.40, 128.44, 140.00, 151.46,
152.85.
Me
O
Cl
O
Me
1
5,5'-((2-Chlorophenyl)methylene)bis(2-methylfuran) (3b):12 Yellow oily liquid. H NMR (400
MHz, CDCl3): δ (ppm) 2.240 (s, 6H), 5.297 (s, 1H), 5.883 (s, 4H), 7.114–7.140 (m, 1H), 7.215–
7.236 (m, 3H). 13C NMR (100 MHz, CDCl3): δ (ppm) 13.61, 44.75, 106.16, 108.46, 126.63,
127.20, 128.54, 129.66, 134.23, 142.05, 151.71, 151.96.
9

1
5,5'-((3-Chlorophenyl)methylene)bis(2-methylfuran) (3c):12 Yellow oily liquid. H NMR (400
MHz, CDCl3): δ (ppm) 2.234 (s, 6H), 5.840–5.878 (m, 5H), 7.172–7.186 (m, 3H), 7.346–7.371
13
(m, 1H). C NMR (100 MHz, CDCl3): δ (ppm) 13.64, 41.62, 106.11, 108.75, 126.85, 128.26,
129.60, 129.94, 133.82, 137.46, 151.56, 151.66.
1
5,5'-((4-Chlorophenyl)methylene)bis(2-methylfuran) (3d):3 Yellow liquid. H NMR (400 MHz,
CDCl3): δ (ppm) 2.162 (s, 6H), 5.222 (s, 1H), 5.780–5.809 (m, 4H), 7.097 (d, J = 8.4 Hz, 2H),
7.195 (d, J = 8.4 Hz, 2H). 13C NMR (100 MHz, CDCl3): δ (ppm) 12.54, 43.43, 105.05, 107.27,
127.52, 128.70, 131.71, 137.50, 150.59, 151.18.
5,5'-((4-Methoxyphenyl)methylene)bis(2-methylfuran) (3e):12 Yellow liquid. 1H NMR (400 MHz,
CDCl3): δ (ppm) 2.168 (s, 6H), 3.714 (s, 3H), 5.208 (s, 1H), 5.761–5.803 (m, 4H), 6.773 (d, J =
8.8 Hz, 2H), 7.092 (d, J = 8.4 Hz, 2H). 13C NMR (100 MHz, CDCl3): δ (ppm) 13.63, 44.30, 55.24,
106.01, 107.97, 113.80, 129.36, 132.15, 151.36, 153.17, 158.53.
5,5'-(p-Tolylmethylene)bis(2-methylfuran) (3f):3 Yellow liquid. 1H NMR (400 MHz, CDCl3): δ
(ppm) 2.159 (s, 6H), 2.246 (s, 3H), 5.218 (s, 1H), 5.770–5.5.788 (m, 4H), 7.024–7.076 (s, 4H).
13C NMR (100 MHz, CDCl3): δ (ppm) 12.57, 20.03, 43.71, 104.98, 106.97, 127.19, 128.08,
135.46, 136.00, 150.30, 152.02.
10

1
5,5'-(Thiophen-2-ylmethylene)bis(2-methylfuran) (3g):3 Yellow liquid. H NMR (400 MHz,
CDCl3): δ (ppm) 2.274 (s, 6H), 5.603 (s, 1H), 5.904–5.913 (m, 2H), 5.995 (d, J = 2.8 Hz, 2H),
6.891–6.904 (m, 1H), 6.937–6.959 (m, 1H), 7.213 (dd, J = 5.2 Hz and 1.2 Hz, 1H). 13C NMR (100
MHz, CDCl3): δ (ppm) 13.63, 40.15, 106.17, 107.88, 124.52, 125.61, 126.56, 143.22, 151.55,
152.16.
3,3'-(Phenylmethylene)bis(2,5-dimethylfuran) (3h):3 Yellow oil. 1H NMR (400 MHz, CDCl3): δ
(ppm) 2.056 (s, 6H), 2.123 (s, 6H), 4.851 (s, 1H), 5.651 (s, 2H), 7.102–7.209 (m, 5H). 13C NMR
(100 MHz, CDCl3): δ (ppm) 11.69, 13.60, 37.92, 107.33, 121.93, 126.04, 128.10, 128.20, 143.96,
145.41, 149.22.
1
3,3'-(Phenylmethylene)bis(1H-indole) (3i):3 White solid. H NMR (400 MHz, CDCl3): δ (ppm)
5.798 (s, 1H), 6.509 (d, J = 2.4 Hz, 2H), 6.924 (d, J = 7.6 Hz, 2H), 7.066–7.319 (m, 11H), 7.715
13
(s, 2H). C NMR (100 MHz, CDCl3): δ (ppm) 40.19, 111.07, 119.23, 119.67, 119.95, 121.93,
123.66, 126.16, 127.07, 128.25, 128.75, 136.66, 144.02.
3,3'-(Phenylmethylene)bis(5-nitro-1H-indole) (3j):3 Yellowish solid. 1H NMR (600 MHz, DMSO-
d6): δ (ppm) 6.066 (s, 1H), 6.998 (s, 1H), 7.085–7.268(m, 5H), 7.402 (d, J = 8.8 Hz, 2H), 7.832
11

13
(d, J = 8.0 Hz, 2H), 8.179 (s, 2H), 11.544 (br, 2H). C NMR (150 MHz, DMSO-d6): δ (ppm)
54.98, 112.19, 116.28, 116.70, 120.59, 125.83, 126.46, 127.66, 128.26, 128.53, 139.85, 140.23,
143.82.
1
3,3'-(Phenylmethylene)bis(5-bromo-1H-indole) (3k):3 Yellowish solid. H NMR (400 MHz,
CDCl3): δ (ppm) 5.758 (s, 1H), 6.652–6.657 (m, 2H), 7.250 (d, J = 0.8 Hz, 3H), 7.271 (s, 2H),
7.296–7.311 (m, 4H), 7.477 (s, 2H), 8.131 (s, 2H).
NH
Me
Me
NH
3,3'-(Phenylmethylene)bis(2-methyl-1H-indole) (3l):3 White solid. 1H NMR (400 MHz, CDCl3):
δ (ppm) 1.985 (s, 6H), 5.936 (s, 1H), 6.782 (t, J = 7.6 Hz, 2H), 6.898–6.983 (m, 4H), 7.153–7.223
(m, 7H), 7.642–7.676 (m, 2H). 13C NMR (100 MHz, CDCl3): δ (ppm) 29.71, 39.23, 109.94,
113.39, 119.04, 119.32, 120.58, 125.95, 128.09, 129.07, 130.95, 131.80, 135.02, 143.72.
3,3'-(Phenylmethylene)bis(5-methoxy-1H-indole) (3m):3 Yellowish solid. 1H NMR (400 MHz,
CDCl3): δ (ppm) 3.626 (s, 6H), 5.711 (s, 1H), 6.601–6.609 (m, 2H), 6.732–6.777 (m, 4H), 7.169–
7.238 (m, 5H), 7.274–7.299 (m, 2H), 7.791–7.804 (m, 2H). 13C NMR (100 MHz, CDCl3): δ (ppm)
40.28, 55.60, 101.92, 111.68, 111.87, 119.26, 124.45, 126.43, 127.92, 128.67, 128.72, 131.85,
143.93, 153.66.
12

3,3'-(Phenylmethylene)bis(1-methyl-1H-indole) (3n):3 White solid. 1H NMR (400 MHz, CDCl3):
δ (ppm) 3.573 (s, 6H), 5.807 (s, 1H), 6.446 (s, 2H), 6.894–6.993 (m, 2H), 7.096–7.140 (m, 3H),
7.175–7.213 (m, 4H), 7.261–7.318 (m, 4H). 13C NMR (100 MHz, CDCl3): δ (ppm) 32.71, 40.14,
109.12, 118.29, 118.69, 120.09, 121.47, 126.08, 127.50, 128.25, 128.32, 128.74, 137.45, 144.51.
3,3'-(Phenylmethylene)bis(1-benzyl-1H-indole) (3o):3 White solid. 1H NMR (400 MHz, CDCl3):
δ (ppm) 5.174 (s, 4H), 5.916 (s, 1H), 6.635 (s, 2H), 6.936–7.008 (m, 6H), 7.069–7.110 (m, 2H),
7.168–7.272 (m, 11H), 7.347–7.402 (m, 4H). 13C NMR (100 MHz, CDCl3): δ (ppm) 39.81, 49.46,
109.27, 118.35, 118.49, 119.75, 121.22, 125.67, 125.98, 129.93, 127.33, 127.49, 127.81, 128.21,
128.30, 136.57, 137.43, 143.65.
5,5'-(Phenylmethylene)bis(2-methylthiophene) (3p):13 Yellow oil. 1H NMR (400 MHz, CDCl3): δ
13
(ppm) 2.411 (s, 6H), 5.672 (s, 1H), 6.566–6.590 (m, 4H), 7.219–7.313 (m, 5H). C NMR (100
MHz, CDCl3): δ (ppm) 14.88, 47.27, 124.03, 125.19, 126.49, 127.82, 127.95, 138.59, 143.31,
144.75.
1
(Phenylmethylene)bis((4-methoxyphenyl)sulfane) (3q):3 Yellow liquid. H NMR (400 MHz,
CDCl3): δ (ppm) 3.741 (s, 6H), 5.159 (s, 1H), 6.755 (d, J = 8.8 Hz, 4H), 7.209–7.285 (m, 9H). 13C
13

NMR (100 MHz, CDCl3): δ (ppm) 55.31, 62.99, 114.36, 124.81, 127.83, 127.92, 128.33, 135.96,
140.16, 159.96.
1,3,5-Trimethoxy-2-((4-methoxyphenyl)(phenyl)methyl)benzene (4a):3 Pale yellow oil. 1H NMR
(400 MHz, CDCl3): δ (ppm) 3.587 (s, 6H), 3.775 (s, 3H), 3.798 (s, 3H), 5.998 (s, 1H), 6.143 (s,
2H), 6.779 (d, J = 8.8 Hz, 2H), 7.108–7.170 (m, 5H), 7.191–7.228 (m, 2H). 13C NMR (100 MHz,
CDCl3): δ (ppm) 43.78, 54.69, 54.75, 55.23, 91.11, 112.46, 124.67, 126.98, 128.38, 129.68,
135.54, 144.13, 156.88, 158.55, 159.41.
1
4-Methyl-N-(phenyl(2,4,6-trimethoxyphenyl)methyl)benzenesulfonamide (4b):2 White solid. H
NMR (400 MHz, CDCl3): δ (ppm) 2.198 (s, 3H), 3.515 (s, 6H), 3.638 (s, 3H), 5.778 (s, 2H), 6.005
(d, J = 10.8 Hz, 1H), 6.147 (d, J = 10.8 Hz, 1H), 6.901 (d, J = 8.0 Hz, 2H), 7.094–7.161 (m, 5H),
7.402 (d, J = 8.0 Hz, 2H). 13C NMR (100 MHz, CDCl3): δ (ppm) 21.37, 51.49, 55.31, 55.59, 90.54,
108.73, 126.43, 126.58, 126.84, 127.91, 128.66, 137.54, 141.29, 142.39, 157.89, 160.86.
1
1,3,5-Trimethoxy-2-(phenoxy(phenyl)methyl)benzene (4c): Yellow liquid. H NMR (400 MHz,
CDCl3): δ (ppm) 3.584 (s, 6H), 3.798 (s, 3H), 5.979 (s, 1H), 6.143 (s, 2H), 6.69 (d, J = 8.8 Hz,2H),
7.063–7.256 (m, 8H). 13C NMR (100 MHz, CDCl3): δ (ppm) 44.48, 55.44, 55.90, 91.83, 113.99,
114.59, 125.39, 127.68, 129.08, 130.53, 136.41, 144.71, 153.45, 159.23, 160.10. Anal. Cacld. (%)
for C22H22O4: C 75.41, H 6.33; Found: C 75.46, H 6.29.
11. References
14

(1) Zeng, J. H.; Wang, Y. F.; Gou, S. Q.; Zhang, L. P.; Chen, Y.; Jiang, J. X.; Shi, F. ACS Appl.
Mater. Interfaces 2017, 9, 34783.
(2) Paul, D.; Borah, A.; Khatua, S.; Chatterjee P. N. Asian J. Org. Chem. 2019, 8, 1870.
(3) Paul, D.; Khatua, S.; Chatterjee, P. N. ChemistrySelect 2018, 3, 11649.
(4) Rao, C. N. R.; Venkataraghavan, R.; Kasturi, T. R. Can. J. Chem. 1964, 42, 36.
(5) Suganuma, S.; Nakajima, K.; Kitano, M.; Hayashi, S.; Hara, M. ChemSusChem 2012, 5, 1841.
(6) Kundu, S. K.; Singuru, R.; Hayashi, T.; Hijikata, Y.; Irle, S.; Mondal, J. ChemistrySelect 2017,
2, 4705.
(7) Du, M.; Agrawal, A. M.; Chakraborty, S.; Garibay, S. J.; Limvorapitux, R.; Choi, B.;
Madrahimov, S. T.; Nguyen, S. T. ACS Sustain. Chem. Eng. 2019, 7, 8126.
(8) (a) Deka, N.; Patidar, R.; Kasthuri, S.; Venkatramaiah, N.; Dutta, G. K. Mater. Chem. Front.
2019, 3, 680. (b) Nath, I.; Chakraborty, J.; Heynderickx, P. M.; Verpoort, F. Appl. Catal. B:
Environmental 2018, 227, 102.
(9) Silvestre-Albero, J.; Silvestre-Albero, A.; Rodríguez-Reinoso, F.; Thommes, M. Carbon 2012,
50, 3128.
(10) Ravishankar, T. N.; Ramakrishnappa, T.; Nagaraju, G.; Rajanaika, H. ChemistryOpen 2015,
4, 146.
(11) Bhunia, S.; Banerjee, B.; Bhaumik, A. Chem. Commun. 2015, 51, 5020.
(12) Thirupathi, P.; Soo Kim, S. J. Org. Chem. 2010, 75, 5240.
(13) Dhiman, S.; Ramasastry, S. Org. Biomol. Chem. 2013, 11, 8030.
15

12. 1H and 13C NMR spectra of products 3 and 4
5,5'-(Phenylmethylene)bis(2-methylfuran) (3a)
16

5,5'-((2-Chlorophenyl)methylene)bis(2-methylfuran) (3b)
17

5,5'-((3-Chlorophenyl)methylene)bis(2-methylfuran) (3c)
18

5,5'-((4-Chlorophenyl)methylene)bis(2-methylfuran) (3d)
19

5,5'-((4-Methoxyphenyl)methylene)bis(2-methylfuran) (3e)
20

5,5'-(p-Tolylmethylene)bis(2-methylfuran) (3f)
21

5,5'-(Thiophen-2-ylmethylene)bis(2-methylfuran) (3g)
22

3,3'-(Phenylmethylene)bis(2,5-dimethylfuran) (3h)
23

3,3'-(Phenylmethylene)bis(1H-indole) (3i)
24

3,3'-(Phenylmethylene)bis(5-nitro-1H-indole) (3j)
25