Epoxidation of Alkenes with Molecular Oxygen as the Oxidant in the Presence of Nano-Al 2O 3

Article abstract of DOI:10.1055/s-0040-1707264

The nano-Al ₂O ₃-promoted epoxidation of alkenes with molecular oxygen as the oxidant has been developed, providing an efficient route to a variety of epoxides in moderate to excellent yields. The environmentally friendly and efficient nano-Al ₂O ₃catalyst could be easily recovered and reused five times without significant loss of activity.

Full text of DOI:10.1055/s-0040-1707264

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Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart
2020, 31, A–F
letter
A
en
X. Zhou et al.
Letter
Synlett
Epoxidation of Alkenes with Molecular Oxygen as the Oxidant in
the Presence of Nano-Al2O3
Xuan Zhou
nano-Al2O3 (10 mol%)
Qiong Wang
Wenfang Xiong
Lu Wang
R1
R2
O
R3
R4
R1
R2
R3
R4
O2
+
3,5,5-trimethylhexanal (3 equiv)
MeCN, 60 °C, 24–36 h
18 examples
up to 96% yield
Rongkai Ye
Ge Xiang
Chaorong Qi*
Jianqiang Hu*
School of Chemistry and Chemical Engineering, South China
University of Technology, Guangzhou 51064, P. R. of China
crqi@scut.edu.cn
jqhusc@scut.edu.cn
Corresponding Author
Chaorong Qi
Received: 24.06.2020
Accepted after revision: 03.08.2020
Published online: 01.09.2020
a) Previous work
Ni, Co, Mn, Cu, Pd, Ru
DOI: 10.1055/s-0040-1707264; Art ID: st-2020-k0223-l
aldehyde
R1
R2
O
R3
R4
R1
R2
R3
R4
Abstract The nano-Al2O3-promoted epoxidation of alkenes with mo-
lecular oxygen as the oxidant has been developed, providing an efficient
route to a variety of epoxides in moderate to excellent yields. The envi-
ronmentally friendly and efficient nano-Al2O3 catalyst could be easily
recovered and reused five times without significant loss of activity.
+
O2
b) This work
nano-Al2O3
3,5,5-trimethylhexanal
Scheme 1 Nano-Al2O3-catalyzed epoxidation of alkenes with molecu-
Key words alkenes, nano-alumina, epoxidation, epoxides, molecular
lar oxygen
oxygen
Recently, some metal oxides have been utilized as cata-
lysts for the epoxidation of alkenes.15 For example, Wang et
al. reported the synthesis of a novel hybrid Fe3O4–CuO@me-
so-SiO2 catalyst which displayed excellent activity in the
catalytic epoxidation of styrene with TBHP as the oxi-
dant.15a Suib’s group reported that mesoporous cobalt oxide
could act as an efficient catalyst for the epoxidation of ole-
fins, and the catalyst could be recycled and reused up to
several times without the loss of activity.15b Mizuno et al.
reported the efficient heterogeneous epoxidation of alkenes
by using a supported tungsten oxide catalyst.15e Despite
these impressive contributions, metal-oxide-catalyzed oxi-
dation of alkenes to epoxides with molecular oxygen or air
as the terminal oxidant under mild reaction conditions is
underdeveloped.
As our continuous interest in the synthesis of nanoma-
terials and their application in the field of catalysis,16 here-
in, we wish to report the epoxidation of olefins with molec-
ular oxygen in the presence of nano-Al2O3 as the catalyst
and 3,5,5-trimethylhexanal as co-reductant (Scheme 1, b).
A variety of epoxides could be obtained by our protocol, and
the nano-Al2O3 was easily recovered and reused at least five
times without significant deactivation.
Epoxidation of alkenes represents an important process
in both industry and academia, because epoxides are versa-
tile intermediates in organic synthesis.1 Moreover, epoxides
are widely used as monomers for the production of func-
tional polymers.2 Therefore, the development of effective
catalysts for the epoxidation of alkenes is of great signifi-
cance.
Over the past decades, numerous catalyst systems have
been developed for the epoxidation by using different oxi-
dizing agents such as iodosylbenzene,3 sodium periodate,4
peroxy acid,5 alkyl hydroperoxides,6 and hydrogen perox-
ide.7 Recently, molecular oxygen as the terminal oxidant
has attracted increasing attention due to its abundance in
nature, ease of handling, and environmentally friendly
character.8 Many transition-metal catalysts, including Ni,9
Cu,10 Co,11 Pd,12 Ru,13 and Mn14 have been reported for the
aerobic epoxidation of alkenes in the presence of aldehydes
as the co-reductant (Scheme 1, a). Although great progress
has been made in this field, the development of cheap and
efficient heterogeneous catalysts for the epoxidation of
alkenes is still highly desirable.
© 2020. Thieme. All rights reserved. Synlett 2020, 31, A–F
Georg Thieme Verlag KG, Rüdigerstraße 14, 70469 Stuttgart, Germany

B
X. Zhou et al.
Letter
Synlett
Initially, 1-phenyl-1-cyclohexene (1a) was employed as
the model substrate for the optimization of the reaction
conditions (Table 1).17 We found that when the reaction
was carried out in the presence of 10 mol% of commercially
available chromatography Al2O3 as the catalyst and 3,5,5-
trimethylhexanal as the co-reductant under 1 atm of mo-
lecular oxygen at 60 °C in MeCN, the desired product 2a was
obtained in 78% yield (entry 1). TiO2 could also promote the
reaction to give 2a in slightly lower yield while other metal
oxides examined such as Fe3O4, ZnO, ZrO2, and CeO2 gave in-
ferior results (entries 2–6). To our delight, when nano-Al2O3
with the average diameter of around 100 nm was used as
the catalyst, the yield of 2a was improved to 90% along with
little amount of allylic oxidation byproduct (entry 7). It
should be pointed out that, in this case, 1.4 mmol of 3,5,5-
trimethylhexanoic acid could be isolated as the coproduct
together with 1.3 mmol of 3,5,5-trimethylhexanal being re-
covered unchanged. These results demonstrated that a part
of the reacted 3,5,5-trimethylhexanal (approximately 30%)
was oxidized to 3,5,5-trimethylhexanoic acid without oxi-
dation of 1a. It was found that the usage amount of the al-
dehyde has a significant influence on the yield of the target
product 2a. The employment of 3 equivalents of 3,5,5-
trimethylhexanal was optimal since more or less amount of
the aldehyde resulted in decreased yields (entries 7–10).
Notably, the reaction could be conducted under ambient at-
mosphere of air instead of molecular oxygen, albeit giving
2a in a lower yield (entry 11). Further optimization showed
that decreasing or increasing the amount of nano-Al2O3
would lead to low yields (entries 12 and 13). Screening of
different solvents revealed that the solvent has a great im-
pact on the oxidation, and MeCN proved to be the best sol-
vent for the transformation (entries 7, 14–17). Moreover,
the reaction was found to be sensitive to the reaction tem-
perature. For example, when the reaction was conducted at
50 °C, only a low yield of 20% was observed due to the low
conversion of 1a; while higher temperature resulted in the
formation of a large amount of unidentified products, and
only little amount of 1a was detected (entries 18 and 19). A
control experiment showed that in the absence of the
nano-Al2O3 catalyst the reaction could occur but gave 2a in
a relatively low yield and selectivity (entry 20), revealing
that the use of the nano-Al2O3 catalyst was crucial to
achieve efficient and selective aerobic epoxidation of 1a.
Then, the effect of various aldehydes as the co-reduc-
tant on the epoxidation of 1a was further investigated un-
der the similar conditions. As can be seen from Figure 1, the
reaction could not occur in the absence of any aldehyde, in-
dicating that the aldehyde was essential for the transforma-
tion. Moreover, among the aldehydes investigated, 3,5,5-
trimethylhexanal was found to be the most effective (col-
umn 7). Other acyclic and cyclic aliphatic aldehydes, includ-
ing the commonly used isobutyraldehyde, trimethylacetal-
dehyde, isovaleraldehyde, valeraldehyde, pelargonic alde-
hyde, and cyclohexanecarbaldehyde, gave the desired
Table 1 Optimization of the Reaction Conditionsa
Ph
Ph
O
catalyst
O2, aldehyde, solvent
1a
2a
Entry
Catalyst
Solvent
Selectivity (%)b
Yield (%)c
1
2
Al2O3
TiO2
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
EtOAc
DMF
87
79
78
76
14
trace
11
4
3
Fe3O4
ZnO
>99
>99
>99
>99
93
4
5
ZrO2
CeO2
6
7
nano-Al2O3
nano-Al2O3
nano-Al2O3
nano-Al2O3
nano-Al2O3
nano-Al2O3
nano-Al2O3
nano-Al2O3
nano-Al2O3
nano-Al2O3
nano-Al2O3
nano-Al2O3
nano-Al2O3
–
90 (84)
41
65
84
82
57
70
56
n.d.
3
8d
9e
90
90
10f
11g
12h
13i
14
15
16
17
18j
19k
20
85
82
89
75
>99
–
CHCl3
MeOH
MeCN
MeCN
MeCN
>99
>99
91
8
20
4
4
72
44
a Reaction conditions: 1a (1 mmol), 3,5,5-trimethylhexanal (3 mmol), catalyst
(10 mol%), solvent (5 mL), O2 (1 atm, balloon), 60 °C, 24 h.
b The selectivity was determined by 1H NMR analysis.
c Yield based on 1H NMR analysis of the crude product using dibromometh-
ane as an internal standard; number in parentheses is the yield of isolated
product.
d 3,5,5-Trimethylhexanal (1 mmol).
e 3,5,5-Trimethylhexanal (2 mmol).
f 3,5,5-Trimethylhexanal (3.5 mmol).
g The reaction was carried out under ambient atmosphere of air.
h 5 mol% of catalyst.
i 15 mol% of catalyst.
j The reaction was performed at 50 °C.
k The reaction was performed at 70 °C.
product 2a in relatively low yields and selectivity (columns
2–6, 8). Aromatic aldehydes, such as benzaldehyde and 3-
methylbenzaldehyde, were also examined, but both of
them exhibited low efficiency (columns 9 and 10).
With the optimal reaction conditions in hand, we then
turned out attention to the substrate scope of the aerobic
epoxidation by using nano-Al2O3 as the catalyst (Table 2).
Pleasingly, a wide range of alkenes could undergo the oxida-
tion to give rise to the corresponding epoxides (2b–r) in
moderate to excellent yields. It was found that the yield and
selectivity was strongly depended on the structure of the
alkene employed. Terminal aliphatic alkenes, such as 1-oc-
© 2020. Thieme. All rights reserved. Synlett 2020, 31, A–F

C
X. Zhou et al.
Letter
Synlett
tene (1b) and 1-decene (1c), which are frequently regarded
as challenging substrates in epoxidation, could furnish the
desired products 2b and 2c in 63% and 75% yield, respec-
tively, with excellent selectivity. As expected, 1-allyl-2-
methylbenzene (1d) and but-3-en-1-ylbenzene (1e) exhib-
ited similar reactivity to 1b. However, the epoxidation of
styrene (1f) showed lower selectivity (71%), and styrene ox-
ide (2f) was obtained in 69% yield after 36 h, together with
large amount of benzaldehyde and 2-phenylacetaldehyde as
the byproducts (ca. 20%). Functional groups on the benzene
ring of the substrates were tolerated. For example, 1-bro-
mo-3-vinylbenzene (1g) could be transformed into the cor-
responding product 2g albeit in a lower yield. The oxida-
tions of cis- and trans-stilbene were also investigated. It was
showed that trans-stilbene (1h) was almost quantitatively
transformed into trans-stilbene oxide (2h). In contrast, the
reaction of cis-stilbene (1i) gave a mixture of cis-and trans-
stilbene oxide in 78% NMR yield with a cis/trans ratio of
42:58. These results suggested that the reaction might pro-
ceed through a benzyl radical intermediate. ,-Unsaturat-
ed carbonyl compounds 1j and 1k were also suitable sub-
strates for the reaction, giving rise to the desired products
in moderate yields with excellent selectivity under the
standard conditions.
Notably, a range of cinnamyl esters 1l–o were compati-
ble with the reaction conditions, enabling the synthesis of
useful epoxides 2l–o in high yields. Trisubstituted alkene
1p displayed a relatively low reactivity to the reaction,
which might partially be due to the steric hindrance effect.
Moreover, both unsaturated bridged-ring hydrocarbon 1q
and 1,4-dihydro-1,4-epoxynaphthalene (1r) could enter
into the aerobic oxidation smoothly, affording the exo prod-
ucts 2q and 2r in 90% and 96% yields, respectively. The
structures of 2q and 2r were further confirmed by NOE
studies and X-ray crystallographic analysis (Figure 2),18 re-
spectively.
Figure 1 Effect of various aldehydes on the aerobic epoxidation of 1a.
Reagents and conditions: 1a (1.0 mmol), aldehyde (3 mmol), nano-Al2O3
(10 mol%), MeCN (5 mL), O2 (1 atm, balloon), 60 °C, 24 h. The yield and
selectivity were determined by 1H NMR spectroscopy with dibromo-
methane as the internal standard.
Table 2 Substrate Scope of Alkenesa
Entry
1
Alkene
Product
Time (h)
24
Selectivity (%)b
>99d
Yield (%)c
63
O
1b
2b
2c
O
2
3
24
24
>99d
>99d
75
60
1c
1d
1e
O
2d
2e
O
4
5
6
24
36
24
>99
71d
61
62
69
57
O
1f
2f
O
Br
Br
1g
2g
© 2020. Thieme. All rights reserved. Synlett 2020, 31, A–F

D
X. Zhou et al.
Letter
Synlett
Entry
7
Alkene
Product
Time (h)
24
Selectivity (%)b
>99
Yield (%)c
95 (>99)
O
1h
1i
2h
8
9
24
24
24
24
24
24
24
24
>99
>99
>99
>99
>99
>99
>99
43
(78, cis/trans = 42:58)
O
2h + 2i
O
O
O
O
O
O
O
O
O
O
O
58 (63)
1j
2j
O
O
O
O
O
O
10
11
12
13
14
15
51
1k
1l
2k
O
O
O
O
O
O
76
2l
O
O
86
1m
1n
1o
1p
2m
2n
O
O
82
O
O
88 (93)
2o
O
O
34
2p
O
16
17
24
24
>99
>99
90 (97)
1q
1r
2q
2r
O
O
O
96 (>99)
a Reaction conditions: 1 (1 mmol), 3,5,5-trimethylhexanal (3 mmol), catalyst (10 mol%), solvent (5 mL), O2 (1 atm, balloon), 60 °C, 24 h.
b The selectivity was determined by 1H NMR analysis.
c Isolated yield; number in parentheses is the yield based on 1H NMR analysis of the crude product using dibromomethane as an internal standard.
d The selectivity was determined by GC–MS and 1H NMR analysis.
Although the nano-Al2O3 catalyst is commercially avail-
able and very cheap, its stability and reusability were fur-
ther evaluated because it is crucial for the development of
an eco-friendly and cost-effective process for the produc-
tion of epoxides. The catalyst was recycled and reused for
several consecutive runs with the model reaction of 1a. In
© 2020. Thieme. All rights reserved. Synlett 2020, 31, A–F

E
X. Zhou et al.
Letter
Synlett
each cycle experiment, the nano-Al2O3 was separated from
the reaction mixture by centrifugation, washed with EtOAc,
and dried at 60 °C under vacuum before being used in the
next run. As shown in Figure 3, no obvious loss of activity
was observed after six consecutive runs, indicating the
good recyclability and stability of the nanocatalyst. The re-
cycled catalyst was also characterized by SEM and XRD, and
no significant changes have been found in comparison with
the catalyst before being used (Figure S1 and Figure S2 in
the Supporting Information).
On the basis of the above results and previous litera-
ture,9–14,19 a plausible mechanism for the epoxidation of
alkenes is proposed as shown in Scheme 2. Initially, acyl
radical A is generated from 3,5,5-trimethylhexanal (3) in
the presence of nano-Al2O3. Then, A reacts with molecular
oxygen to produce an acylperoxy radical B, which can ab-
stract a hydrogen atom from another aldehyde molecule to
give peroxyacid C. Finally, the epoxidation of alkene 1a with
peroxyacid C will occur to give the product 2a accompany-
ing the formation of carboxylic acid 4 (Path a). Alternatively,
the acylperoxy radical B may add to the double bond of 1a
to give an intermediate D. Subsequent decomposition of D
will give the epoxide 2a and radical E. Radical E can then
react with another aldehyde molecule to yield carboxylic
acid 4 (Path b). Considering that cis-stilbene gave a mixture
of cis- and trans-stilbene oxides under our conditions, nei-
ther of the two pathways can be excluded at present and, in
some cases, they might operate concurrently.9b,11c,19
Ph
1a
CO3H
CO2H
Ph
O
C
4
A
2a
3
Path a
nano-Al2O3
O2
CHO
CO3
Ph
CO
B
A
3
Path b
1a
Ph
O
A
Ph
2a
CO2
4
CO3
3
E
D
Scheme 2 Plausible mechanism of reaction
In summary, we have successfully demonstrated a
nano-Al2O3-promoted epoxidation of alkenes with molecu-
lar oxygen as the oxidant and 3, 5, 5-trimethylhexanal as
co-reductant. A variety of alkenes could undergo the reac-
tion under mild conditions, giving the corresponding epox-
ide products in moderate to excellent yields. The eco-
friendly nano-Al2O3 catalyst could be easily recovered and
reused five times without significant loss of activity.
Funding Information
This work was supported by the National Natural Science Foundation
of China (21673081 and 21971073) and the Natural Science Founda-
tion
of
Guangdong
Province
(2018B0303110002
and
2019A1515011468).
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Supporting Information
Figure 2 X-ray crystal structure of compound 2r.
Supporting information for this article is available online at
https://doi.org/10.1055/s-0040-1707264.
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References and Notes
(1) (a) Mulzer, M.; Coates, G. W. J. Org. Chem. 2014, 79, 11851.
(b) Bedore, M. W.; Zaborenko, N.; Jensen, K. F.; Jamison, T. F.
Org. Process Res. Dev. 2010, 14, 432. (c) Shaikh, R. R.;
Pornpraprom, S.; D’Elia, V. ACS Catal. 2018, 8, 419. (d) He, J.;
Ling, J.; Chiu, P. Chem. Rev. 2014, 114, 8037.
(2) (a) Liu, Y.; Deng, K.; Wang, S.; Xiao, M.; Han, D.; Meng, Y. Polym.
Chem. 2015, 6, 2076. (b) Longo, J. M.; Sanford, M. J.; Coates, G.
W. Chem. Rev. 2016, 116, 15167. (c) Herzberger, J.; Niederer, K.;
Pohlit, H.; Seiwert, J.; Worm, M.; Wurm, F. R.; Frey, H. Chem. Rev.
2016, 116, 2170.
Figure 3 Reusability of the nano-Al2O3. Reagents and conditions: 1a
(1.0 mmol), 3,5,5-trimethylhexanal (3 mmol), nano-Al2O3 (10 mol%),
MeCN (5 mL), O2 (1atm, balloon), 60 °C, 24 h.
© 2020. Thieme. All rights reserved. Synlett 2020, 31, A–F

F
X. Zhou et al.
Letter
Synlett
(3) (a) Mukerjee, S.; Stassinopoulos, A.; Caradonna, J. P. J. Am. Chem.
Soc. 1997, 119, 8097. (b) Murakami, Y.; Konishi, K. J. Am. Chem.
Soc. 2007, 129, 14401. (c) Wang, B.; Lee, Y. M.; Seo, M. S.; Nam,
W. Angew. Chem. Int. Ed. 2015, 54, 11740.
(14) (a) Hadian-Dehkordi, L. H.; Hosseini-Monfared, H.; Aleshkevych,
P. Inorg. Chim. Acta 2017, 462, 142. (b) Brown, J. W.; Nguyen, Q.
T.; Otto, T.; Jarenwattananon, N. N.; Glöggler, S.; Bouchard, L.-S.
Catal. Commun. 2015, 59, 50.
(4) Bahramian, B.; Mirkhani, V.; Moghadam, M.; Tangestaninejad, S.
Catal. Commun. 2006, 7, 289.
(15) (a) Zhang, X.; Wang, G.; Yang, M.; Luan, Y.; Dong, W.; Dang, R.;
Gao, H.; Yu, J. Catal. Sci. Technol. 2014, 4, 3082. (b) Weerakkody,
C.; Biswas, S.; Song, W.; He, J.; Wasalathanthri, N.; Dissanayake,
S.; Kriz, D. A.; Dutta, B.; Suib, S. L. Appl. Catal., B 2018, 221, 681.
(c) Hadian-Dehkordi, L. H.; Hosseini-Monfared, H. Green Chem.
2016, 18, 497. (d) Phon-in, P.; Seubsai, A.; Chukeaw, T.; Charoen,
K.; Donphai, W.; Prapainainar, P.; Chareonpanich, M.; Noon, D.;
Zohour, B.; Senkan, S. Catal. Commun. 2016, 86, 143. (e) Kamata,
K.; Yonehara, K.; Sumida, Y.; Hirata, K.; Nojima, S.; Mizuno, N.
Angew. Chem. Int. Ed. 2011, 50, 12062.
(5) Jensen, A. J.; Luthman, K. Tetrahedron Lett. 1998, 39, 3213.
(6) (a) Shokouhimehr, M.; Piao, Y.; Kim, J.; Jang, Y.; Hyeon, T.
Angew. Chem. Int. Ed. 2007, 46, 7039. (b) Banerjee, D.; Jagadeesh,
R. V.; Junge, K.; Pohl, M.-M.; Radnik, J.; Brückner, A.; Beller, M.
Angew. Chem. Int. Ed. 2014, 53, 4359.
(7) (a) Lane, B. S.; Burgess, K. Chem. Rev. 2003, 103, 2457. (b) Cussó,
O.; Ribas, X.; Lloret-Fillol, J.; Costas, M. Angew. Chem. Int. Ed.
2015, 54, 2729. (c) Dias, L. D.; Carrilho, R. M. B.; Henriques, C. A.;
Calvete, M. J. F.; Masdeu-Bultj, A. M.; Claver, C.; Rossi, L. M.;
Pereira, M. M. ChemCatChem 2018, 10, 2792. (d) Kamata, K.;
Yonehara, K.; Sumida, Y.; Hirata, K.; Nojima, S.; Mizuno, N.
Angew. Chem. Int. Ed. 2011, 50, 12062.
(16) (a) Feng, X.; Ruan, F.; Hong, R.; Ye, J.; Hu, J.; Hu, G.; Yang, Z.
Langmuir 2011, 27, 2204. (b) Ye, R.; Zhang, Y.; Chen, Y.; Tang, L.;
Wang, Q.; Wang, Q.; Li, B.; Zhou, X.; Liu, J.; Hu, J. Langmuir 2018,
34, 5719.
(8) (a) Allen, S. E.; Walvoord, R. R.; Padilla-Salinas, R.; Kozlowski, M.
C. Chem. Rev. 2013, 113, 6234. (b) Weinstock, I. A.; Schreiber, R.
E.; Neumann, R. Chem. Rev. 2018, 118, 2680.
(9) (a) Mukaiyama, T.; Yamada, T. Bull. Chem. Soc. Jpn. 1995, 68, 17.
(b) Wentzel, B. B.; Alsters, P. L.; Feiters, M. C.; Nolte, R. J. M.
J. Org. Chem. 2004, 69, 3453.
(10) (a) Yang, G.; Du, H.; Liu, J.; Zhou, Z.; Hu, X.; Zhang, Z. Green
Chem. 2017, 19, 675. (b) Qi, Y.; Luan, Y.; Yu, J.; Peng, X.; Wang, G.
Chem. Eur. J. 2015, 21, 1589. (c) Li, Z.; Wu, S.; Ding, H.; Zheng, D.;
Hu, J.; Wang, X.; Huo, Q.; Guan, J.; Kan, Q. New J. Chem. 2013, 37,
1561.
(17) Typical Procedure for the Synthesis of Epoxide 2a
To a 25 mL dried Schlenk tube was added the mixture of nano-
Al2O3 (10.2 mg), alkene 1a (1.0 mmol), 3,5,5-trimethylhexanal
(3.0 mmol) in dry MeCN (5 mL) successively. The resulting
mixture was stirred at 60 °C for 24 h under 1 atm of O2. After the
reaction was completed, the reaction mixture was cooled to
room temperature, diluted with EtOAc (25 mL), and filtered.
After removing the solvent under vacuum, the crude product
was separated by column chromatography on silica gel using
PE–EtOAc as eluent to give the product 2a as a pale-yellow oil;
yield 84%. IR (KBr): 3060, 2933, 1450, 966, 859, 749, 543 cm–1
.
(11) (a) Maksimchuk, N. V.; Melgunov, M. S.; Chesalov, Y. A.; Białoń,
J. M.; Jarzębski, A. B.; Kholdeeva, O. A. J. Catal. 2007, 246, 241.
(b) Reddy, M. M.; Punniyamurthy, T.; lqbal, J. Tetrahedron Lett.
1995, 36, 159. (c) Nam, W.; Kim, H. J.; Kim, S. H.; Ho, R. Y. N.;
Valentine, J. S. Inorg. Chem. 1996, 35, 1045.
(12) He, X.; Chen, L.; Zhou, X.; Ji, H. Catal. Commun. 2016, 83, 78.
(13) Mekrattanachai, P.; Liu, J.; Li, Z.; Cao, C.; Song, W. Chem.
Commun. 2018, 54, 1433.
MS (EI): m/z = 174 [M+]. 1H NMR (500 MHz, CDCl3):  = 7.27–
7.11 (m, 5 H), 2.95 (d, J = 3.5 Hz, 1 H), 2.19–2.13 (m, 1 H), 2.02–
1.97 (m, 1 H), 1.92–1.81 (m, 2 H), 1.53–1.41 (m, 2 H), 1.38–1.31
(m, 1 H), 1.24–1.15 (m, 1 H). 13C NMR (126 MHz, CDCl3):  =
142.6, 128.3, 127.2, 125.3, 61.9, 60.2, 28.9, 24.8, 20.2, 19.8.
(18) CCDC 2019579 contains the supplementary crystallographic
data for compound 2r. The data can be obtained free of charge
from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/getstructures.
(19) Tsuchiya, F.; Ikawa, T. Can. J. Chem. 1969, 47, 3191.
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