Cu-doped zeolitic imidazolate framework catalysed highly selective conversion of alkynes to β -keto and vinyl sulfones using sodium sulfinates

Article abstract of DOI:10.1007/s12039-018-1582-5

Abstract: Cu ^{2 +}-doped zeolitic imidazolate framework-8 (ZIF-8)-catalyzed one-pot procedure to synthesize β -keto and vinyl sulfones by the direct oxysulfonylation and hydrosulfonylation of alkynes via radical reaction under mild conditions has been described. The advantages of this protocol included broad substrate scope and excellent β -keto and E-stereoselectivity. The Cu/ZIF-8 catalyst not only exhibited excellent performance but also had a great stability in the reaction, successfully allowing its reuse up to five cycles. This efficient Cu/ZIF-8 heterogeneous catalyst is explored for the first time to generate β -keto and vinyl sulfones. Graphical Abstract:: Cu ^{2 +}-doped zeolitic imidazolate framework-8 (ZIF-8)-catalyzed one-pot procedure to synthesize β -keto and vinyl sulfones by the direct oxysulfonylation and hydrosulfonylation of alkynes via radical reaction under mild conditions is described. The advantages of this protocol included broad substrate scope and excellent β -keto and E-stereoselectivity. This efficient Cu/ZIF-8 heterogeneous catalyst is explored for the first time for C-S bond formation. [Figure not available: see fulltext.].

Full text of DOI:10.1007/s12039-018-1582-5

J. Chem. Sci.
(2019) 131:8
© Indian Academy of Sciences
https://doi.org/10.1007/s12039-018-1582-5
REGULAR ARTICLE
Cu-doped zeolitic imidazolate framework catalysed highly
selective conversion of alkynes to β-keto and vinyl sulfones using
sodium sulfinates
NAGESWARA RAO YALAVARTHI, NARAYANARAO GUNDOJU, RAMESH BOKAM and
MANGALA GOWRI PONNAPALLI∗
Centre for Natural Products and Traditional Knowledge, CSIR-Indian Institute of Chemical Technology,
Hyderabad, Telangana 500 007, India
E-mail: mangala@iict.res.in
MS received 26 July 2018; revised 23 October 2018; accepted 12 November 2018
Abstract. Cu2+-doped zeolitic imidazolate framework-8 (ZIF-8)-catalyzed one-pot procedure to synthesize
β-keto and vinyl sulfones by the direct oxysulfonylation and hydrosulfonylation of alkynes via radical reaction
under mild conditions has been described. The advantages of this protocol included broad substrate scope and
excellent β-keto and E-stereoselectivity. The Cu/ZIF-8 catalyst not only exhibited excellent performance but
also had a great stability in the reaction, successfully allowing its reuse up to five cycles. This efficient Cu/ZIF-8
heterogeneous catalyst is explored for the first time to generate β-keto and vinyl sulfones.
Keywords. Phenyl acetylenes; Cu/ZIF-8; β-Keto and vinyl sulfone.
1. Introduction
ZIF-8 structure should enable its use as a reusable
heterogeneous catalyst in organic reactions.10
Methods for the formation of C–S bonds are
considered as an important tool in synthetic organic
chemistry. These are used as versatile building
blocks15–17 in biomedical research. Particularly, vinyl
sulfones are a novel class of neuroprotective agents
toward Parkinson’s therapy,16 anti-trypanosomal
agents18 and β-keto sulfones as inhibitors of 11β-
hydroxysteroid dehydrogenase type I.19 Over the years,
a number of procedures were made available for the
preparation of vinyl and β-keto sulfones.20–28 However,
the major drawbacks of some of these methods include
longer reaction periods, high temperatures and the for-
mation of side products. Hence, the development of a
new protocol for the synthesis of vinyl and β-keto sul-
fones using reusable heterogeneous catalyst is highly
beneficial.
In recent years, there is a growing interest in the use of
copper nanoparticles as a catalyst due to their significant
physicalandchemicalpropertiesaswellasabroadrange
of applications.1–3 The capability of copper to attain var-
ious oxidation states makes it a suitable candidate for the
synthesis of nanoparticles with varying composition. On
the other hand, zeolitic imidazolate framework (ZIFs)
materials constitute a new distinctive and rapidly devel-
oping subclass of metal-organic frameworks (MOFs).
In particular, ZIF-8 is the most investigated ZIF mate-
rial for a variety of applications including heterogeneous
catalysis,7–12 gas sorption4 and sensing.5,6 Its applica-
tion as an efficient heterogeneous catalyst support has
been demonstrated recently for various reactions such
as Knoevenagel reaction,13,14 1,3-dipolar cycloaddi-
tions, Friedlander and Combes condensations.10 Based
on these observations, we focused our efforts on the
use of Cu2+-doped ZIF-8 as a heterogeneous cata-
lyst for exploring new protocols for the synthesis of
organic scaffolds. The presence of Cu2+ ions in the
A literature survey revealed that homogeneous
copper catalyzed sulfonylation of alkynes with sodium
p-toluenesulfinate provides alkenyl sulfones with a
trace amount of β-keto sulfones or β-hydroxyl sulfones
*
For correspondence
Electronic supplementary material: The online version of this article (https://doi.org/10.1007/s12039-018-1582-5) contains
supplementary material, which is available to authorized users.
0123456789().: V,-vol

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J. Chem. Sci.
(2019) 131:8
as by-products.27,28 These reports not only encouraged 2.3 Synthesis of (E)-Vinyl sulfones
us to initiate the heterogeneous catalysis but also
Phenyl acetylene 1a (0.5 mmol, 1 equiv.), sodium 4-methylbe
directed us to investigate the oxysulfonylation and
hydrosulfonylation of alkynes under mild conditions.
Moreover, transition metals like Cu, Pd can transfer
a single electron and are easily oxidized or reduced
under certain conditions.22–28 Herein, we report Cu2+-
doped nanoparticles supported on ZIF-8 as an efficient
heterogeneous catalyst for hydrosulfonylation and oxy-
sulfonylation of alkynes under relatively mild operating
conditions. To the best of our knowledge, this is the first
nzenesulfinate 2a (0.6 mmol, 1.2 equiv.), Cu25%/ZIF-8
(0.05 mmol, 0.1 equiv.) and acetonitrile (2 mL) were added to
a 5 mL glass tube at room temperature and stirred for 3 h and
monitored periodically by TLC. Then the reaction mixture
was extracted with ethyl acetate (3 × 5 mL) and dried over
anhydrous Na2SO4. The solvent was removed under reduced
pressure, and the crude product was purified by silica gel
column chromatography using petroleum ether and ethyl
acetate (9:1 v/v) as eluent to give the pure product
report on the formation of the C–S bond using hetero- 3a.
geneous Cu2+-doped ZIF-8 as a catalyst.
3. Results and Discussion
2. Experimental
Cu2+-doped zeolitic imidazolate frameworks (ZIFs)
crystals were synthesized following the same proto-
col reported in the literature.10 After preparation, these
crystals were denoted as Cu1%/ZIF-8, Cu7%/ZIF-8,
Cu15%/ZIF-8, and Cu25%/ZIF-8. The synthesized cata-
lyst was characterized by FT-IR (Figure S1), UV (Figure
S2), X-ray diffraction analysis (XRD) (Figure S3), scan-
ning electron microscopy (SEM) (Figure S4), and also
compared with reported data.10 The advantage of using
ZIF-8 as the support is due to its ease of preparation,
large surface area, and stability in acids, bases, water
and even in the presence of methanol.
2.1 Materials and physical measurements
All the reagents and solvents were purchased as
commercial grade and used as received. IR spectra were
recorded on a Nicolet-740 FT-IR spectrophotometer with
KBr pellets. The NMR spectra were recorded with Bruker
1
Avance (300/400/500 MHz) for H, and 100/125 MHz for
13C NMR spectra in CDCl3 with TMS as an internal standard.
Coupling constants are given in Hz. The ESI MS data were
recorded on an Agilent 1100 MSD with ESI SL Trap. The
HR-ESIMS data were acquired on an Agilent 6510 Q-TOF
and ESI probe. Scanning electron microscopy (SEM) pictures
were prepared using a JEOL Scanning Electron Microscope
JSM-6490 LV. The powder samples were placed on a sili-
con zero-background sample holder and the XRD patterns
Initially, we performed the oxysulfonylation of
phenylacetylene (1) with sodium p-toluenesulfinate (2)
in the presence of Cu1%/ZIF-8, Cu7%/ZIF-8, Cu15%
/
ZIF-8, Cu25%/ZIF-8 in ethanol at room temperature
for 12 h, the desired product 3a was obtained in 65%
yield with Cu25%/ZIF-8 (Table 1, entry 5). Interest-
ingly, the yield of 3a was improved markedly to 89%
when methanol was introduced into the Cu25%/ZIF-8
catalyzed reaction system. These results indicated that
methanol played a very significant role in the reac-
tion. Methanol gives better yield compared to other
solvents like ethanol, isopropanol, tert-butyl alcohol
(Table 1, entry 4–8). A careful solvent survey indicated
that methanol improved the yield compared to ethanol,
isopropanol, tert-butyl alcohol, and water (Table 1,
entry 4). Subsequently, various copper doping ZIF-
8 catalysts Cu1%/ZIF-8, Cu7%/ZIF-8, Cu15%/ZIF-8,
Cu25%/ZIF-8 were treated as the catalysts. Cu25%/ZIF-
8 was proved to be the best choice and the target
product 3a was obtained in 89% yield (Table 1,
entry 4).
α
were recorded at room temperature using Cu K radiation
(
= 0.15418 nm). The textural properties of the mate-
λ
rials were investigated with a Micromeritics ASAP 2420
instrument using liquid nitrogen (−196 ◦C). Prior to the anal-
yses, the samples were out-gassed overnight in vacuum at
40 ◦C on the degassing port followed by 4 h out-gassing
on the analyse port. Diffuse reflectance UV-Vis spectra of
the samples were measured using a Shimadzu UV-2101 PC
spectrophotometer and spectra are recorded in a range of
200–700 nm.
2.2 Synthesis of β-keto sulfones
Phenyl acetylene 1a (0.5 mmol, 1 equiv.), sodium 4-methylbe
nzenesulfinate 2a (0.6 mmol, 1.2 equiv.), Cu25%/ZIF-8
(0.05 mmol, 0.1 equiv.) and methanol were added to a 5 mL
glass tube at room temperature and stirred for 12 h and
monitored periodically by TLC. Then the reaction mixture
was extracted with ethyl acetate (3 × 5 mL) and dried over
anhydrous Na2SO4. The solvent was removed under reduced
pressure, and the crude product was purified by silica gel col-
umn chromatography using petroleum ether and ethyl acetate
(8:2 v/v) as eluent to give the pure product 4a.
With optimized reaction conditions in hand, we
next examined the substrate scope. Therefore, a range
of substituted aromatic alkynes were chosen to react
with Cu25%/ZIF-8 and the results are summarized

J. Chem. Sci.
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Page 3 of 8
8
Table 1. Optimization of β-ketosulfone reaction conditionsa.
Entry
Catalyst
Solvent
Yieldb(%)
1
2
3
4
5
6
7
8
9
Cu1%/ZIF-8
Cu7%/ZIF-8
Cu15%/ZIF-8
Cu25%/ZIF-8
Cu25%/ZIF-8
Cu25%/ZIF-8
Cu25%/ZIF-8
Cu25%/ZIF-8
–
CH3OH
CH3OH
CH3OH
Trace
45
65
89
65
Trace
0
Trace
0
CH3OH
CH3CH2OH
(CH3)2CHOH
(CH3)3COH
H2O
CH3OH
aReaction conditions: Phenyl acetylene
1
(0.5 mmol,
1
equiv.), sodium 4-
methylbenzenesulfinate 2 (0.6 mmol, 1.2 equiv.), Cu25%/ZIF-8 (5 mol%) in methanol
at room temperature. bIsolated yields. The bold letters signify the optimized and final
reaction conditions.
Table 2. Scope of the β-ketosulfone reaction of various alkynes with sodiumsulfinatea,b
.
aReaction conditions: 1 (0.5 mmol), 2 (0.6 mmol), Cu25%/ZIF-8 (5 mol%), MeOH (3 mL),
12 h. bIsolated yields based on 1.
in Table 2. Halo groups such as (Br, F and OCF3) aromatic rings such as pyren-1-yl and 6-methoxy
were well-tolerated in the reaction system to provide naphthalene-2-yl alkynes afforded the corresponding
β-keto sulfones in excellent yields (Table 2). Bulky products in good yields (Table 2). Next, we turned

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Table 3. Optimization of the vinyl sulfone reaction conditionsa.
J. Chem. Sci.
(2019) 131:8
Entry
Catalyst
Solvent
Yieldb (%)
1
2
3
4
5
6
7
8
Cu25%/ZIF-8
Cu25%/ZIF-8
Cu25%/ZIF-8
Cu25%/ZIF-8
Cu25%/ZIF-8
Cu25%/ZIF-8
Cu25%/ZIF-8
Cu25%/ZIF-8
Cu25%/ZIF-8
Cu1%/ZIF-8
Cu7%/ZIF-8
Cu15%/ZIF-8
–
THF
CH3CN
DME
DMF
DMSO
DCM
1,4-Dioxane
EtOAc
H2O
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
0
88
80
78
69
0
58
76
0
9
10
11
12
13
14
Trace
45
74
0
Cu25%/ZIF-8
88c
aReaction conditions: Phenyl acetylene
1
(0.5 mmol, 1 equiv.), Sodium 4-
methylbenzenesulfinate 2 (0.6 mmol, 1.2 equiv.), Cu25%/ZIF-8 (5 mol%) in acetonitrile
(3 mL) at room temperature. bIsolated yields. cReaction carried at 50 ◦C, 80 ◦C, 100 ◦C. The
bold letters signify the optimized and final reaction conditions.
our focus towards hydrosulfonylation, in order to check the desired product (12 h) was obtained in 72% yield
the generality of the transformation in the presence of (Table 4).
Cu15%/ZIF-8 (5 mol%) in CH3CN at room temperature
After completion of the reaction, the catalyst was
for 12 h to afford (Table 3, entry 12) vinyl sulfone (4a) separated by centrifugation and washed thoroughly with
in 74% yield. A variety of other copper doped catalysts methanol, dried overnight at 100 ◦C and used directly
Cu1%/ZIF-8, Cu7%/ZIF-8, Cu15%/ZIF-8, Cu25%/ZIF-8 for the next round of reaction. We noticed that catalyst
were investigated in CH3CN (Table 3, entry 2, 10–12). was reused five cycles without any significant loss of
Cu25%/ZIF-8 accomplished 4a in 88% yield (Table 3, activity.
entry 2). To check the effect of temperature on the
To gain a better understanding of the reaction
reaction, the test reaction was carried out at different mechanism, a series of control experiments related to
temperatures (Table 3, entry 14). It was observed that radicals were performed (Scheme 1). When the rad-
the maximum conversion occurred at room temperature ical scavenger reagent TEMPO (2,2,6,6-tetramethyl
in 12 h, providing the desired product 4a in 88% yield piperadinyloxy, awell-knownradical-capturingspecies)
(Table 3, entry 2). A higher temperature didn’t improve and DPE (1,1-diphenylethylene) were introduced into
the yield.
the standard reaction system, no products (3a and 4a)
With optimized reaction conditions in hand, we next were detected in both cases and the starting materi-
examined the substrate scope (Table 4) on als were recycled, indicating that the reactions were
substituents bearing either an electron donating or elec- completely inhibited by TEMPO/DPE (Scheme 1). This
tron withdrawing groups on the aromatic ring. All strongly suggests that both the reactions have been pre-
reacted smoothly to furnish the desired vinyl sulfones ceded through a radical mechanism. When aliphatic
with excellent E-stereo selectivity in good to excellent terminal alkynes were introduced into the standard
yields (Table 4), a number of functional groups (OMe, conditions, no product was observed whereas internal
Br, F, CF3, and CH3) were tolerated under optimized alkyne yielded the product 5a (Scheme 1).
conditions. Heterocyclic alkyne was also suitable for
A plausible reaction mechanism for oxysulfonylation
this transformation and corresponding vinyl sulfone and hydrosulfonylation from these results and rele-
was obtained in 67% yield (4f). When 6-methoxy vant literature29–38 is illustrated in Scheme 2. In the
naphthalene-2-yl substituted alkyne was treated with first step, sodium p-toluene sulfinate is oxidized in the
sodium p-toluenesulfinate under standard conditions, presence of Cu(II) catalyst and sulfonyl radical A is

J. Chem. Sci.
(2019) 131:8
Page 5 of 8
8
Table 4. Scope of the vinyl sulfone reaction of various alkynes with sodium sulfinatea,b
.
aReaction conditions: 1 (0.5 mmol), 2 (0.6 mmol), Cu25%/ZIF-8(5 mol%), CH3CN (3 mL),
12 h. bIsolated yields based on 1.
Scheme 1. Control experiments.
generated, which reacts with an alkyne to give a radical abstraction of a hydrogen atom, the peroxy radical
intermediate B. In the next step, radical B is trapped transforms into hydro peroxide,39–41 which transforms
with oxygen forming peroxy radical. Sequentially, after to D (Scheme 2), and gives the main product 3a after

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J. Chem. Sci.
(2019) 131:8
Scheme 2. A plausible oxysulfonylation and hydrosulfonylation mechanism using
the example of the reaction of phenyl acetylene 1a and sodium p-toulenesulfinate
2a.
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Characterization data and copies of 1H, 13C NMR spectra are
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Mild Oxidative Aryl Radical Addition into Alkenes by