An efficient heterogeneous copper fluorapatite (CuFAP)-catalysed oxidative synthesis of diaryl sulfone under mild ligand- and base-free conditions

Article abstract of DOI:10.1039/c8nj04845b

A simple, eco-friendly and efficient method for the synthesis of unsymmetrical diaryl sulfones using heterogeneous copper fluorapatite (CuFAP)-catalysed coupling of aryl sulfonic acid and phenyl boronic acid has been developed with good to excellent yields without use of any ligand, base or co-catalyst. Broad substrate scope and gram scale operations are the important features of this method.

Full text of DOI:10.1039/c8nj04845b

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An efficient heterogeneous copper fluorapatite
(CuFAP)-catalysed oxidative synthesis of diaryl
sulfone under mild ligand- and base-free
Cite this: New J. Chem., 2019,
43, 1632
conditions†
ab
Rohit B. Kamble,ab Santosh S. Chavanc and Gurunath Suryavanshi
*
Received 24th September 2018,
Accepted 10th December 2018
A simple, eco-friendly and efficient method for the synthesis of unsymmetrical diaryl sulfones using
heterogeneous copper fluorapatite (CuFAP)-catalysed coupling of aryl sulfonic acid and phenyl boronic
acid has been developed with good to excellent yields without use of any ligand, base or co-catalyst.
Broad substrate scope and gram scale operations are the important features of this method.
DOI: 10.1039/c8nj04845b
rsc.li/njc
Diaryl sulfones are important synthetic intermediates1 due to
their interesting chemical2 and biological3 properties. These
moieties are known to exhibit promising antitumor and anti-
fungal activities and inhibition of HIV-1 reverse transcriptase.4
Furthermore, they act as useful building blocks in numerous
drugs such as migraine medication Eletriptan,5 antibacterial
Dapsones,6 sFRPÀ1 inhibitor,7 Laropiprant,8 a prostaglandin D2
antagonist, and COX-2 inhibitor Vioxx9 (Fig. 1).
Sulfone also plays an important role as an inhibitor of parasitic
infections, which include leishmaniasis10 and malaria.11 Arylsul-
fones are important synthetic targets and are extensively used
synthons in many industrial applications.12 In addition, sulfones
and their derivatives are distinctive structural frameworks13
widely useful in organic transformations such as the Ramberg–
Backlund reaction14 and Julia olefination.15 Due to the impor-
tance of diaryl sulfones, various metal and metal-free approaches
have been published in the literature for the synthesis of diaryl
Fig. 1 Bioactive compounds having aryl sulfone motifs.
sulfones. The most conventional methods are the oxidation of which was effectively utilized for the synthesis of diaryl sulfones
sulphides and sulfoxides.1,16 Also, sodium sulfinate salts can be using Pd- and Cu-catalysed cross-coupling of a Grignard reagent,
efficiently utilised for the preparation of diaryl sulfones under organolithium compounds and aryl halides (Scheme 1).19 The
metal and metal-free conditions with a wide range of reagents arylsulfinic acid salts are coupled with aryl halide or aryl boronic
such as boronic acids,17a,b aryl halides17c–e and phenyliodonium acids using Pd- or Cu-catalysts, which have milder reaction
salts17f,g (Scheme 1). Transition metals such as Pd and Cu are conditions; on the other hand, the use of toxic and expensive
extensively used for the preparation of sulfones under oxidative transition metals limits the use of such preparations. Recently,
cross-coupling reactions of sodium sulfinate salts,18a sulfonyl transition-metal-free synthesis of diaryl sulfones was established
hydrazone,18b,c and phenyldiazonium salts18d with aryl halides. with arylsulfinic acid, organometallic reagents and diaryliodonium
Willis and co-workers introduced a new sulfonyl reagent ‘‘DABSO’’, salts.22 More recently, diaryl sulfones were prepared by cross-
coupling of sodium and lithium sulfinate with aryl iodide using a
a Chemical Engineering & Process Development Division, CSIR-National Chemical
Laboratory, Dr Homi Bhabha Road, Pune, Maharashtra, 411008, India.
E-mail: gm.suryavanshi@ncl.res.in
b Academy of Scientific and Innovative Research (AcSIR), Ghaziabad 201 002, India
c Post Doctorate Fellow at Okinawa Institute of Science and Technology, Japan
† Electronic supplementary information (ESI) available. CCDC 1862593. For ESI and
crystallographic data in CIF or other electronic format see DOI: 10.1039/c8nj04845b
photoredox/Ni catalyst,20a singlet oxygen-induced oxidation of
aryl thiols and aryl diazonium salts using silver catalysis and
visible light,20b and Ni-catalysed photoredox sulfinylation of aryl
and vinyl halides.20c In spite of the various routes for the
synthesis of diaryl sulfones, there are many limitations that could
pose a problem: limited substrate sources, use of expensive noble
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Table 1 Optimization of reaction conditionsa
Entry
Solvent
Time (h)
Yieldb (%)
1
2
3
4
5
6
7
8
DCE
DCM
MeCN
DMF
DMSO
PhMe
THF
1,4-Dioxane
EtOH
MeOH
t-BuOH
IPA
MeOH
MeOH
MeOH
24
24
24
24
24
24
24
24
12
12
12
12
12
12
12–24
64
43
70
N.R.
N.R.
N.R.
66
75
90
95
88
81
96
94
52
9
10
11
12
13c
14d
15e
a
Reaction conditions: 1a (1.2 mmol), 2a (1.0 mmol) and CuFAP
b
(100 mg) in solvent (4 mL) at rt for 12–24 h. Isolated yield. N.R. =
no reaction. CuFAP (75 mg). CuFAP (50 mg). CuFAP (25 mg).
c
d
e
short reaction time. Methanol was found to be the most
effective solvent to produce the desired compound 3a in 95%
yield (entry 10). Next, we screened the catalyst loading, in which
it was observed that decreasing catalyst loading from 75 mg to
50 mg (entries 13 and 14) also showed excellent performance to
Scheme 1
metal complexes, harsh reaction conditions, use of air- or moisture- deliver the compound 3a in a good yield.
sensitive reagents, incompatibility with various functional groups,
After optimizing the reaction conditions, we explored the
etc. Therefore, it is imperative that a simple, convenient and substrate scope and generality of the heterogeneous recyclable
generally applicable protocol for synthesis of aryl sulfones be CuFAP-catalysed synthesis of diaryl sulfones (Table 2).
established.
First, various arylboronic acids 2b–2r were reacted with 1a
To the best of our knowledge, there are no reports to date on under optimized reaction conditions to provide the desired
the utilization of a heterogeneous CuFAP catalyst for the synthesis diaryl sulfones in moderate to good yields (Table 2, entries
of diaryl sulfones. However, it has been extensively studied in the 3a–3r). This protocol is practically remarkable with various
formation of C–C, C–O and C–N bonds. As a part of our present arylboronic acids having both electron-donating and electron-
study on the development of new synthetic methodologies and withdrawing substituents on the aryl ring. With a variety of
organic transformation over heterogeneous catalysts,21 herein, we functional groups such as t-Bu, Me, OMe, and OPh present at
disclose an environmentally benign protocol for the synthesis of para and meta positions of the arylboronic acid, disubstituted
diaryl sulfones using a heterogeneous CuFAP catalyst under mild diarylboronic acids are also well tolerated under standard
reaction conditions with good to excellent yields.
reaction conditions, giving excellent yields of desired diaryl
We started our investigation by combining sodium p-toluene sulfones (entries 3a–3f). Moreover, phenylboronic acids bearing
sulfinate 1a with phenylboronic acid 2a in the presence of reactive functional groups such as –NHAc, –NMe2, and –CHQCH2
heterogeneous CuFAP as the catalyst in 4 mL solvent as the were successfully reacted to afford the corresponding products in
model reaction. Initially, a series of solvents were screened over 72 to 85% yields (entries 3g–3j). The substrates having electron-
the CuFAP catalyst (Table 1, entries 1–12) at room temperature. withdrawing substituents on the aromatic ring of boronic acids,
The reaction afforded 43 to 70% yield of desired diaryl sulfone for example, –I, –Cl, –F, and –NO2 and disubstituted boronic acids
3a in DCE, DCM, and MeCN solvents (entries 1–3). The reaction were efficiently reacted to produce substituted diaryl sulfones in
failed to deliver the product in aprotic solvents such as DMF, slightly lower yields (entries 3k–3q). Also, 3-thiopheneboronic acid
DMSO, and PhMe.
under optimized reaction conditions afforded the desired product
After careful adjustments, we found that THF and 1,4-dioxane in 95% yield (entry 3r). When sodium 4-fluorobenzenesulfinate
were less effective in the reaction, affording the corresponding and sodium 2-nitrobenzenesulfinate were reacted with p-tolylboronic
product 3a in 66 to 75% yield. However, protonated solvents acid under standardized reaction conditions, they delivered
provided high yields of desired compounds (entries 8–12) in a the expected diarylsulfones in 69 and 65% yields, respectively
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Table 2 Substrate scope of diaryl sulfones over heterogenous CuFAP
catalysta,b
Table
3
Substrate scope of phenyldiazonium tetrafluoroborate over
heterogeneous CuFAP catalysta,b
a
Reaction conditions: 1a (1.2 mmol), 4a (1.0 mmol) and CuFAP (50 mg)
b
in MeOH (4 mL) at rt for 12 h. Isolated yield.
and the results are shown in Table 3. To our delight, the reaction
successfully afforded the desired unsymmetrical diaryl sulfones in
good to excellent yields. It is noteworthy that the electron donating
group –OMe gave the highest yield, i.e., 94% (entry 5b), whereas
electron withdrawing groups, such as –F, –I and 2-NO2, delivered
comparatively lower yields (entries 5c–5e).
On the basis of previously reported data on CuFAP catalysts21
and in continuation of our previous study on C–O and C–C bond
formation reactions,22 a possible reaction mechanism for this
heterogeneous CuFAP-catalysed synthesis of diaryl sulfones is
shown in Fig. 2.
Initially, sodium phenyl sulfinate reacts with the CuFAP
catalyst to generate an intermediate complex (I). Subsequently,
complex (I) undergoes addition of phenylboronic acid to form
complex (II), which instantly undergoes interconversion of C–S
bond formation via reductive elimination to deliver the diaryl-
sulfone product (III) and the CuFAP catalyst in its original form
to be recycled.
Due to increasing worldwide environmental concerns, recover-
ability and recyclability of catalysts are highly desirable.
a
Reaction conditions: 1a (1.2 mmol), 2a (1.0 mmol) and CuFAP (50 mg)
b
c
in MeOH (4 mL) at rt for 12 h. Isolated yield. Sodium 4-fluoro-
benzenesulfinate. 2-Nitrobenzenesulfinate. Sodium pyridine-4-sulfinate
d
e
coupled with p-tolylboronic acid.
(entries 3s and 3t). In contrast, when the reaction was carried
out using sodium pyridine-4-sulfinate with phenyl boronic acid
as well as p-tolylboronic acid, it failed to deliver the expected
products (entries 3u and 3v).
To demonstrate the versatility of this environmentally benign
protocol, a range of phenyldiazonium tetrafluoroborates as coupling
partners were evaluated.
Thus, different substituted phenyldiazonium tetrafluoroborates
4a–4e were subjected to reaction under our optimized conditions,
Fig. 2 Plausible reaction mechanism.
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Table 4 Recoverability and reusability of CuFAP catalysta
Wiley, New York, 1988; (c) N. S. Smpkins, Sulfones in Organic
Synthesis, Pergamon Press, Oxford, 1993 and references
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Entry
Run
Yieldb (%)
1
2
3
4
5
Fresh
Run-1
Run-2
Run-3
Run-4
94
93
94
91
91
a
Reaction conditions: (1a) phenylboronic acid (1 mmol), (2a) sodium
phenyl sulfinate (1.2 mmol), CuFAP (50 mg) in MeOH (4 mL) at room
b
temperature for 12 h. Isolated yield by column chromatography.
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Hence, the recyclability and recovery of CuFAP catalyst were
investigated for the synthesis of diaryl sulfones from sodium
4-methylphenyl sulfinate with phenylboronic acid under optimized
reaction conditions, and the results are shown in Table 4. The
CuFAP catalyst was recovered quantitatively and reused again
for 4 times without loss of catalytic activity (Table 4, entries 2–5).
The isolated yield obtained after the 4th recycle (Table 4, entry 4)
was consistent with that for fresh CuFAP catalyst for the synthesis
of diarylsulfone.
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Conclusions
In summary, we have demonstrated a simple environmentally
friendly protocol over a heterogeneous recyclable CuFAP catalyst
for the synthesis of diarylsulfones in moderate to good yields.
The described protocol is very compatible with the wide sub-
strate scope and has several advantages over previous methods.
These advantages include mild reaction conditions, high yields
of product, reusability of catalyst and simple experimental
procedure. The CuFAP catalyst was recovered by filtration and
recycled for 4 times without loss of catalytic activity. Furthermore,
the applications of CuFAP catalyst and extension of the scope of the
present methodology are underway in our laboratory.
Conflicts of interest
There are no conflicts to declare.
Acknowledgements
The RBK is highly thankful to CSIR (National Repository of Small
Molecules) for providing fellowship & DST New Delhi for funding.
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