Synthesis of cyclic monothiocarbonates via the coupling reaction of carbonyl sulfide (COS) with epoxides

Article abstract of DOI:10.1039/c5cy00977d

Two guanidine bases were used as organocatalysts for the synthesis of cyclic monothiocarbonates via the coupling reaction of carbonyl sulfide (COS) and epoxides. The systems proved to be efficient single-component, metal-free catalysts for the reaction of

Full text of DOI:10.1039/c5cy00977d

View Article Online
View Journal
Catalysis
Science &
Technology
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: M. Luo, X. Zhang
and D. J. Darensbourg, Catal. Sci. Technol., 2015, DOI: 10.1039/C5CY00977D.
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Accepted Manuscripts are published online shortly after
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the Ethical guidelines still
apply. In no event shall the Royal Society of Chemistry be held
responsible for any errors or omissions in this Accepted Manuscript
or any consequences arising from the use of any information it
contains.
www.rsc.org/catalysis

Please do not adjust margins
Catalysis Science & Technology
Page 1 of 6
View Article Online
DOI: 10.1039/C5CY00977D
Journal Name
ARTICLE
Synthesis of Cyclic Monothiocarbonates via the Coupling Reaction
of Carbonyl Sulfide (COS) with Epoxides
M. Luo,a,b X.-H. Zhanga and D. J. Darensbourgb
Received 00th January 20xx,
Accepted 00th January 20xx
Two guanidine bases were used as organocatalysts for the synthesis of cyclic monothiocarbonates via the coupling
reaction of carbonyl sulfide (COS) and epoxides. The systems proved to be efficient single-component, metal-free catalysts
for the reaction of simple (propylene oxide, 1,3-butene oxide) or activated epoxides (epichlorohydrin, glycidyl phenyl
ether) with COS under solvent-free and mild reaction conditions to selectively afford the corresponding cyclic
monothiocarbonates. The yield of this reaction is generally high, thereby providing ready means for pure product isolation.
DOI: 10.1039/x0xx00000x
www.rsc.org/
triazabicyclo[4.4.0]dec-5-ene (TBD), under solvent-free and
mild reaction conditions. The selectivity of this reaction is very
high, no byproduct is produced, and following the full
conversion of the starting epoxide, minor purification is
needed, the only impurity being a trace amount of catalyst.
Introduction
Inasmuch as there are numerous reports of the catalytic
preparation of cyclic carbonates from a wide variety of
epoxides and CO2, there are no reports of the synthesis of
cyclic monothiocarbonates via a similar process utilizing
carbonyl sulfide.1 Cyclic monothiocarbonates (MTCs) are
important synthetic intermediates in organic2 and polymer
sciences.3 A few synthetic methods have been developed for
the preparation of MTCs, such as the carbonylation of β-
hydroxy thiol with phosgene, the reaction of oxiranes with
sulfur and carbon monoxide in the presence of sodium
hydride, the base-catalyzed cyclization of the imidazolide
derivative prepared by the treatment of epoxy alcohol with
thiocarbonyl diimidazole, the oxidation of 2-alkoxy-1,3-
oxathiolane, and the acid-assisted cyclization of 2-
hydroxyethyl thiocarbonate.2-6 All these methods have their
disadvantages: (i) the use of poisonous phosgene, carbon
monoxide and odorous thiol (ii) multiple component reaction
system, making the purification of the product difficult, and
(iii) harsh reaction condition. In addition, the decarboxylation
of MTCs occasionally occur under these reaction conditions,
and thiirane can be formed as a byproduct.6
Results and Discussion
Initially, we examined the reaction of the simple aliphatic
terminal epoxide, propylene oxide (PO, 1a in Table 1), with
o
carbonyl sulfide (COS) in the presence of TBD at 60 C. After 12
1
hours, 26% of the PO was consumed on the basis of the H
NMR spectrum of the crude product (Figure S1). The cyclic
monothiocarbonate, 5-methyl-1,3-oxathiolan-2-one
(2a in
Table 1), was produced, which was confirmed by NMR, IR, and
Gas Chromatography Mass Spectrometry (GC-MS) (Figure S1-
S4). The crude product was removed from the reactor and no
further purification was undertaken. The yield of product was
calculated after the evaporation of the unreacted PO. In order
to accelerate the reaction, it was carried out at higher
temperatures (entries 2-5, Table 1). Interestingly, higher
reaction temperature initiated oxygen/sulfur scrambling in the
reaction process. An additional cyclic dithiocarbonate, 4-
methyl-1,3-dithiolan- 2-one (3a in Table 1), was produced. 3a
was similarly determined by NMR, IR and GC-MS (Figure S5-
S8). In our previous report on the copolymerization of COS
with PO, 2a and 3a have been observed as reaction byproducts
at elevated reaction temperatures.7 Figure 1 depicts the 1H
NMR spectra of the coupling reaction products obtained at
various temperatures. These spectra clearly illustrate the
relationship between reaction temperature and cyclic product
distribution, with an increase in the percentage of 3a with
increasing temperature. Hence, it is possible by selecting
temperature and/or catalyst to selectively synthesize either 2a
or 3a. That is, using TBD as catalyst at 60 oC only 2a is
In this article, we report on the development of an efficient
and easy-handling method for the synthesis of MTC by the
coupling reaction of epoxides with carbonyl sulfide (COS)
catalyzed by a single compound and metal-free catalyst, 1,5,7-
a.MOE Key Laboratory of Macromolecular Synthesis and Functionalization,
Department of Polymer Science and Engineering, Zhejiang University, Hangzhou
310027, China.
b.Department of Chemistry, Texas A&M University, College Station, Texas 77843,
United States.
† Corresponding Authors: X.-H. Zhang (xhzhang@zju.edu.cn) and D. J. Darensbourg
(djdarens@chem.tamu.edu).
Electronic Supplementary Information (ESI) available: Experimental spectroscopic
data. See DOI: 10.1039/x0xx00000x
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 1
Please do not adjust margins

Please do not adjust margins
Catalysis Science & Technology
Page 2 of 6
ARTICLE
Journal Name
produced, whereas, at 120 oC predominantly 3a (>94%) is The plausible reaction pathways to the formationVoiefw2AarticalenOdnl3inae
DOI: 10.1039/C5CY00977D
2, respectively. As shown in
afforded. Alternatively, employing MTBD as catalyst, the are shown in Scheme 1 and
process is highly selective for producing 2a at all temperatures Scheme 1, the coordination of TBD with COS forms a
investigated.
transiently stable six-membered ring with the oxygen atom of
COS interacting with the N-H proton of TBD via a hydrogen
bond. A similar pathway has been presented by Cantat and
coworkers for the organocatalyzed reductive functionalization
of CO2 in the presence of TBD.8 A crystal structure of the CO2
adduct of TBD has been reported, where a zwitterionic
structure is seen with N···O distance in the N-H···O unit of
2.535(2) Å.9 This is followed by sulfur attack of the PO on the
less hindered carbon leading to an intermediate where an
oxygen anion is formed. 2a is generated by the backbiting of
the oxygen anion on the carbonyl carbon. For the
dithiocarbonate 3a, an oxygen/sulfur scrambling may occur
during the reaction as shown in Scheme 2. At high reaction
temperatures, the oxygen anion can attack another COS with
the formation of a sulfur anion. Subsequently, the sulfur anion
attacks the methine carbon of PO to form a new sulfur anion
with release of CO2. 3a is generated by the backbiting of the
sulfur anion on the carbonyl carbon. In order to verify the
credibility of this pathway, a reaction of CO2 and PO with TBD
was carried out at 120 °C. After 24 hours only trace amount of
cyclic carbonate was observed, with the conversion of PO
being less than 1%. Thus, CO2 does not effectively react with
PO under the condition of TBD as in the presence of COS. This
explains why no cyclic carbonate was observed in entries 2-5.
Figure 1. 1H NMR spectra of the products from PO/COS coupling at different
temperatures. 1H NMR signals for hydrogens in
c and cˊ positions are further
upfield and not shown here, see Figure S28-30.
Table 1. Coupling reaction of COS with PO.
O
N
S
O
N
N
COS
H
2a
S
TBD
N
N
N
Conv.b Yieldc 2ad
3ad 4ae
(%) (%)
Entrya Catalyst T (°C) t (h)
(%)
26
(%)
25
96
96
98
98
40
41
38
95
(%)
100
75
N
C
N
H
N
H
1
2
3
4
5
6
7
8e
TBD
60
12
24
24
12
12
72
48
24
48
0
0
0
0
0
0
0
0
5
7
TBD
70
>99
>99
>99
>99
43
25
37
66
94
0
C
O
O
O
S
TBD
80
63
N
TBD
100
120
70
34
TBD
6
N
C
N
H
O
MTBD
MTBD
MTBD
MTBD
100
100
95
80
45
0
S
O
O
100
120
41
0
9e
>99
93
0
a
The reactions were performed in neat PO (0.5 ml, 2.64 mmol; 1.5
MPa COS was added; catalyst/epoxides = 1/1000 in molar ratio) in a
10 ml autoclave. Determined by 1H NMR spectrum of the crude
b
c
product. The crude product was removed from autoclave to a clean
Scheme 1. The plausible reaction pathway to the generation of 2a catalyzed by
vial, and the isolated yield was calculated after the evaporating of the
TBD.
d
PO. The yield is for the total cyclic products. The molar ratio of 2a
The two pathways shown in Scheme 1 and
2 rely on the N-H
1
e
and 3a was determined by H NMR spectrum of the crude product.
group of TBD to stabilize the orientation of COS and support
subsequent reaction processes.10 Hence, if indeed this is a
necessary requirement for oxygen/sulfur exchange, this
scrambling process should be eliminated upon removing the
N-H function from the organocatalyst. In order to support this
In entries 8 and 9, besides 2a and 3a, another cyclic product 4a: 4-
methyl-1,3-oxathiolan-2-one was produced.
2 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 3 of 6
Catalysis Science & Technology
Please do not adjust margins
Journal Name
hypothesis,
ARTICLE
a
derivative
of
TBD, 7-methyl-1,5,7-
View Article Online
DOI: 10.1039/C5CY00977D
triazabicyclo[4.4.0]dec-5-ene (MTBD), was employed as In order to examine the effect of substituents on the epoxide
catalyst for the coupling reaction. The results of these substrate when coupling with carbonyl sulfide on the cyclic
reactions are provided in Table 1 (entries 6-9).
thiocarbonate product(s), we carried out studies with a variety
of epoxides, and the results are summarized in Table 2. The
aliphatic 1,2-butene oxide (1b, entries 1 and 2 in Table 2)
behaves similarly to propylene oxide, providing cyclic
monothiocarbonate (2b) with 100% selectively at 60 oC, and
the product was well-defined (Figure S14-17). Upon raising the
N
O
COS
N
C
N
H
temperature to 70 oC, about 6% of cyclic dithiocarbonate (3b
was produced as a result of oxygen/sulfur exchange. However,
for the halogen-substituted epoxide, epichlorohydrin (1c
)
S
O
O
COS
N
,
N
N
C
N
H
entries 3-5 in Table 2), the selectivity for the cyclic
monothiocarbonate (2c) was not influenced by reaction
temperatures. Over the temperature range of 70 to 90 °C the
selectivity remained 100%, and the product was well-defined
(Figure S18-21). Notably, this coupling reaction occurred
efficiently with phenyl glycidyl ether (1d, entry 6 in Table 2),
where the coupling of phenyl glycidyl ether with COS was
completed in 12 hours at 60 °C providing selectively 100%
cyclic monothiocarbonate (2d), and the product was well-
defined (Figure S22-25). For the vinyl-substituted epoxide, 1,3-
butadiene oxide (1e, entries 7, 8 in Table 2), no reaction
occurred at 60 °C. However, at 70 oC, 47% of the epoxide
converted to cyclic monothiocarbonate (2e) in 12 hours (Figure
S26). However, because of the reactivity of the vinyl group on
the cyclic product, the thiocarbonate resulted in formation of a
cross-linked compound which was insoluble in most organic
solvents such as chloroform, tetrahydrofuran, and dimethyl
sulphoxide. The phenyl-substituted styrene oxide (1f, entries 9,
10 in Table 2) underwent oxygen/sulfur scrambling at 70 °C,
N
N
H
S
O
O
O
TBD
S
N
O
S
N
N
S
H
C
S
O
S
CO2
3a
Scheme 2. The plausible reaction pathway to the generation of 3a catalyzed by
TBD.
As is evident in Table 1, MTBD is less active as a catalyst
relative to TBD, however it is more selective. For example, at
the lower temperatures of 70 oC and 80 oC the only cycle
product observed was 2a based on 1H NMR spectroscopy.
However, at the higher temperatures of 100 oC and 120 oC,
although no 3a product was found which is indicative of no
oxygen/sulfur scrambling; trace quantities of the other isomer
of 2a, 4-methyl-1,3-oxathiolan-2-one (4a), were produced. 4a
was identified by 1H NMR and GC-MS analysis (Figure S11-S13).
Although, 2a and 4a have the same mass, they afford different
mass fragments in the GC-MS. Only 5 and 7% of 4a were
produced at 100 oC and 120 oC (entries 8 and 9), respectively.
4a results from a difference in the site of the PO ring-opening
step, where in this instance cleavage occurs at the sterically
hindered methine carbon center. Scheme 3 represents
proposed mechanistic pathways for the COS/PO coupling
reaction as catalyzed by MTBD. Presumably, reaction pathway
and both monothiocarbonate (2f) and dithiocarbonate (3f
)
were observed in the crude product. In addition, the reaction
showed no activity at the lower temperature (60 °C).
Therefore, it was impossible to achieve a good selectivity for
the product by adjusting temperature in the coupling of
styrene oxide with COS. Furthermore, utilizing MTBD as
catalyst, there was no reaction between styrene oxide and
COS. In addition, the disubstituted epoxide, cyclohexene oxide,
did not undergo reaction with COS in the presence of TBD at
80 – 110 oC. This is consistent with our earlier report, where
the cyclohexene oxide/COS reaction catalyzed by a zinc-cobalt
double metal cyanide complex provided exclusively copolymer
at 110 oC.11
B
has a higher activation barrier.
Scheme 3. The plausible reaction pathway for the generation of 2a (pathway
and 4a (pathway ) catalyzed by MTBD.
A)
B
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
Please do not adjust margins

Please do not adjust margins
Catalysis Science & Technology
Page 4 of 6
ARTICLE
Table 2. Coupling reactions of COS with various epoxides.
Journal Name
Conclusions
View Article Online
DOI: 10.1039/C5CY00977D
In summary, we have reported a new method for synthesizing
cyclic monothiocarbonate via the coupling reactions of
carbonyl sulfide with epoxides catalyzing by two guanidine
bases TBD and MTBD at mild reaction conditions. These
organocatalysts have proven to be efficient single-compound
and metal-free catalyst for this reaction. The yield of cyclic
thiocarbonate is generally high, thereby, no purification is
needed upon full conversion of the epoxides. For aliphatic
epoxides, cyclic monothiocarbonate or dithiocarbonate can be
selectively synthesized by adjusting the reaction temperature.
However, for epichlorohydrin and phenyl glycidyl ether, the
corresponding cyclic monothiocarbonates are the only
products.
Epoxide
1: R
T
t
Conv.b Yieldc
Entrya
Productd (%)
(°C) (h)
(%)
(%)
1b:
C2H5
1
60 24 33
70 12 63
30
2b: 100%
1b:
2b: 94%
3b: 6%
2
3
4
5
59
25
75
76
C2H5
Experimental section
Materials and Methods
1c:
70 12 27
80 12 77
90 12 78
2c: 100%
2c: 100%
2c: 100%
CH2Cl
Unless otherwise specified, all syntheses and manipulations
were carried out on a double-manifold Schlenk vacuum line
under an atmosphere of argon or in an argon-filled glovebox.
Following purification, materials were stored in an argon-filled
glovebox prior to use. Epoxides (propylene oxide, 1,2-butene
oxide, butadiene monoxide, epichlorohydrin, styrene oxide,
phenyl glycidyl ether) were purchased from Acros or TCI and
distilled over CaH2 before used. Carbonyl sulfide (99.0%, 0.756
lbs) was purchased from Specialty Gases of America Inc., and
used directly. 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) and 7-
1c:
CH2Cl
1c:
CH2Cl
methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene
(MTBD)
were
purchased from Aldrich and dried at 80 °C in vacuum and then
transferred into the glovebox. MTBD was dissolved in dry
dichloromethane as a solution with a concentration of
10μl/ml. Dichloromethane was purified by an MBraun Manual
Solvent Purification System packed with Alcoa F200 activated
1d:
6
60 12 99
98
2d: 100%
-
CH2OPh
1
alumina desiccant. H and 13C NMR spectra were recorded on
1e:
CHCH2
1e:
7
8
9
70 12
80 12 47
60 24
-
-
40
-
Mercury 300 MHz and Inova 300 MHz spectrometers. The
peak frequencies were referenced versus the internal standard
(TMS) shift at 0 ppm for 1H NMR and against the solvent
chloroform-d at 77.0 ppm for 13C NMR.
Cross-linked
product
CHCH2
1f:
Typical procedure for coupling reaction of carbonyl sulfide
and epoxides
-
-
Ph
The coupling reactions of carbonyl sulfide (COS) and epoxides
were performed in a 10 mL autoclave equipped with a
magnetic stirrer and a barometer. In a typical experiment, the
autoclave was firstly dried in an oven for 24 hours and
transferred into the glovebox. 0.5 ml PO and 1mg TBD were
added into the autoclave successively. The autoclave was
pressurized to 1.5 MPa pressure with COS and then placed in
an oil bath of 60 °C, and the reaction mixture was stirred for 6
hours. After reaction, the reactor was cooled in an ice bath to
room temperature and COS was slowly released. An aliquot
was taken from the crude product for the determination of the
conversion rate of epoxide and the percentage of different
1f:
Ph
2f: 43%
3f: 57%
10
70 12 69
60
a The reactions were performed in neat epoxide (0.5 ml at R.T.;
1.5 MPa COS was added; TBD was used as catalyst,
catalyst/epoxides = 1/1000 in molar ratio) in a 10 ml autoclave.
b Determined by using 1H NMR spectroscopy. c The crude
product was removed from autoclave to a clean vial, and the
isolated yield was calculated after the evaporating of the
unreacted epoxide. d The molar ratio of cyclic products were
determined by 1H NMR spectrum of the crude product.
1
cyclic products by H NMR spectra. Subsequently, the crude
4 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 5 of 6
Catalysis Science & Technology
Please do not adjust margins
Journal Name
ARTICLE
Feinauer, M. Jacobi and K. Hamann, ChemisVciheweArBtieclreicOhnltinee,
product was removed and placed into a clean vial, and upon
evaporation of the unreacted epoxide, the product was
weighed in order to calculate the yield. The obtained pure
product was analyzed by 1H NMR, 13C NMR, IR and GC-MS.
1965, 98, 1782-1788.
DOI: 10.1039/C5CY00977D
5
(a) D. D. Reynolds, M. K. Massad, D. L. Fields and D. L.
Johnson, J. Org. Chem., 1961, 26, 5122-5124; (b) D. D.
Reynolds, J. Am. Chem. Soc., 1957, 79, 4951-4952.
S. Hata, H. Goto, S.Tanaka and A. Oku, J. Appl. Polym. Sci.,
2003, 90, 2959-2968.
M. Luo, X. H. Zhang, B. Y. Du, Q. Wang and Z. Q. Fan,
Macromolecules, 2013, 46, 5899-5904.
C. D. N. Gomes, O. Jacquet, C. Villiers, P. Thuery, M.
6
7
8
Characterization of the products
5-methyl-1,3-oxathiolan-2-one (2a).4b IR data in CH2Cl2 (νCO):
1735 cm-1. 1H NMR (CDCl3): δ 1.31 (m, 3H), 3.25 (m, H) 3.53 (m,
H), 4.81 (m, H). 13C NMR (CDCl3): δ 19.81, 38.08, 77.86, 172.83.
GC-MS: 118; Yellow oil. Anal. Calcd. for C4H6O2S: C, 40.66; H,
5.12. Found: C, 40.05; H, 5.23.
Ephritikhine and T. Cantat, Angew. Chem. Int. Ed., 2012, 51
,
187-190.
9
C. Villiers, J.-P. Dognon, R. Pollet, P. Thuery and M.
Ephritikhine, Angew. Chem. Int. Ed., 2010, 49, 3465-34680
10 G. Fiorani, W. Guo and A. W. Kleij, Green Chem., 2015, 17
,
4-methyl-1,3-dithiolan-2-one (3a).12 IR data in CH2Cl2 (νCO):
1650 cm-1. 1H NMR (CDCl3): δ 1.59 (m, 3H), 3.39 (m, H) 3.71 (m,
H), 4.20 (m, H). 13C NMR (CDCl3): δ 20.00, 43.04, 47.99, 197.88.
GC-MS: 134; Yellow oil.
1375-1389.
11 M. Luo, X. H. Zhang, B. Y. Du, Q. Wang and Z. Q. Fan,
Polymer, 2014, 55, 3688-3695.
12 S. Sakai, Y. Fujimura, Y. Ishii, J. Org. Chem., 1970, 35, 2344–
2347.
5-ethyl-1,3-oxathiolan-2-one (2b).4b IR data in CH2Cl2 (νCO):
1
1733 cm-1. H NMR (CDCl3): δ 1.03 (m, 3H), 1.79, 1.90 (m, 2H)
3.28 (m, H), 3.48 (m, H) 4.60 (m, H). 13C NMR (CDCl3): δ 9.68,
27.35, 36.17, 82.73, 172.90. GC-MS: 132; Yellow oil.
5-(chloromethyl)-1,3-oxathiolan-2-one (2c).4b IR data in CH2Cl2
1
(νCO): 1747 cm-1. H NMR (CDCl3): δ 3.56, 3.65 (m, 2H), 3.75,
3.77 (m, 2H), 4.88 (m, H). 13C NMR (CDCl3): δ 33.81, 43.22,
78.48, 171.74. GC-MS: 152; Light yellow oil.
5-(phenoxymethyl)-1,3-oxathiolan-2-one (2d).4c IR data in
1
CH2Cl2 (νCO): 1745 cm-1. H NMR (CDCl3): δ 3.68 (m, 2H), 4.23
(m, 2H), 5.03 (m, H), 6.91, 6.93 (m, 2H), 7.01 (m, H), 7.31 (m,
2H). 13C NMR (CDCl3): δ 33.27, 66.89, 77.89, 114.64, 121.93,
129.79, 157.90, 172.37. GC-MS: 210; White powder.
Acknowledgements
We gratefully acknowledge the financial support of the
National Science Foundation (CHE-1057743) and the Robert A.
Welch Foundation (A-0923). The China Scholarship Council and
National Science Foundation of the People’s Republic of China
(no. 21274123 and 21474083) are also acknowledged for their
support.
Notes and references
1
(a) M. North, R. Pasquale and C. Young, Green Chem., 2010,
12, 1514-1539; (b) A. Decortes, A. M. Castilla and A. W. Kleij,
Angew. Chem. Int. Ed., 2010, 49, 9822-9837; (c) R. Martin
and A. W. Kleij, ChemSusChem., 2011,
4, 1259-1263; (d) P. P.
Pescarmona and M. Taherimehr, Catal. Sci. Technol., 2012,
2
,
2169-2187; (e) X.-B. Lu and D. J. Darensbourg, Chem. Soc.
Rev., 2012, 41, 1462-1484; (f) J. W. Comerford, I. D. V.
Ingram, M. North and X. Wu, Green Chem., 2015, 17, 1966-
1987.
W. R. Roush and D. Gustin, Tetrahedron Lett., 1994, 35
4931-4934.
P. C. Wang, Heterocycles, 1986, 24, 329-369.
(a) Y. Nishiyama, C. Katahira and N. Sonoda, Tetrahedron,
2006, 62, 5803-5807; (b) Y. Taguchi, K. Yanagiya, I. Shibuya
and Y. Suhara, Bull. Chem. Soc. Jpn., 1988, 61, 921-926; (c) R.
2
,
3
4
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
Please do not adjust margins

Catalysis Science & Technology
Page 6 of 6
View Article Online
DOI: 10.1039/C5CY00977D
33x14mm (300 x 300 DPI)