Potassium tert-butoxide-mediated metal-free synthesis of sulfonamides from sodium sulfinates and N,N-disubstituted formamides

Article abstract of DOI:10.1016/j.tetlet.2018.06.031

By using formamides as amine sources, a novel and efficient KO-t-Bu mediated amination of sodium sulfinates has been developed. The reaction utilizes readily available starting materials under metal-free conditions, thus providing an alternative and attractive route to sulfonamides.

Full text of DOI:10.1016/j.tetlet.2018.06.031

Accepted Manuscript
Potassium tert-Butoxide-Mediated Metal-Free Synthesis of Sulfonamides from
Sodium Sulfinates and N,N-Disubstituted Formamides
Xiaodong Bao, Xiaona Rong, Zhiguo Liu, Yugui Gu, Guang Liang, Qinqin Xia
PII:
S0040-4039(18)30773-1
https://doi.org/10.1016/j.tetlet.2018.06.031
TETL 50069
DOI:
Reference:
Tetrahedron Letters
To appear in:
Received Date:
Revised Date:
Accepted Date:
25 April 2018
7 June 2018
11 June 2018
Please cite this article as: Bao, X., Rong, X., Liu, Z., Gu, Y., Liang, G., Xia, Q., Potassium tert-Butoxide-Mediated
Metal-Free Synthesis of Sulfonamides from Sodium Sulfinates and N,N-Disubstituted Formamides, Tetrahedron
Letters (2018), doi: https://doi.org/10.1016/j.tetlet.2018.06.031
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers
we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and
review of the resulting proof before it is published in its final form. Please note that during the production process
errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Potassium tert-Butoxide-Mediated Metal-Free Synthesis of Sulfonamides from
Sodium Sulfinates and N,N-Disubstituted Formamides
Xiaodong Bao a, c, Xiaona Rong b, Zhiguo Liua, Yugui Gub, Guang Liang a, *, Qinqin Xia a, *
a
Chemical Biology Research Center, School of Pharmaceutical Sciences, Wenzhou Medical University,
Wenzhou 325035, People’s Republic of China. Corresponding Authors: wzmcliangguang@163.com (G.
Liang), zdxiaqinqin@163.com (Q. Xia)
b
College of Chemistry and Materials Engineering, Wenzhou University, Wenzhou 325035, People’s
Republic of China
c Department of Pharmacy, Jinhua People’s Hospital, Jinhua, Zhejiang, 321000, People’s Republic of China
Graphical Abstract：
R1
N
KOt-Bu (4.0 equiv), 50 °C,
CH3CN, 15min
1).
2).
O
H
R1
N
R2
O
S
R2
R
ONa
O
NIS (2.0 equiv), 50 °C,
CH3CN, 12 h
S
R
O
ABSTRACT. By using formamides as amine sources, a novel and efficient KO-t-Bu mediated amination of
sodium sulfinates has been developed. The reaction utilizes readily available starting materials under
metal-free conditions, thus providing an alternative and attractive route to sulfonamides.
Keywords: Synthetic methods; Sodium sulfinates; Decarbonylation; Sulfonylation; Sulfonamides
Introduction
Sulfonamides are highly valuable structural motifs in numerous bioactive molecules, pharmaceuticals, and
natural products. They exhibit a broad spectrum of biological activities and are employed extensively in
1

various medicinal and pharmaceutical applications, for example, as antibacterials, anticonvulsants, HIV
protease inhibitors, antitumor agents, and antifungal agents.1 Therefore, considerable efforts have been
devoted to develop a methodology for constructing sulfonamides during the past decade. Conventionally,
sulfonamides can be synthesized by the nucleophilic substitution of amines to sulfonyl chlorides.2 Compared
to sulfonyl chlorides, sodium sulfinates can be considered better sulfonylation reagents because of their
stability, low price and convenience of handling.3 Recently, Jiang and co-workers reported an elegant
CuBr2-catalyzed oxidative synthesis of sulfonamides via the reaction of sodium sulfinates and amines with
DMSO or O2.4 This reaction can also be carried out under metal-free conditions.5 These methods avoid
prefunctionalization of the sulfonate component, thus resulting in greater step and atom economy.
N,N-disubstituted formamides are easy to handle, inexpensive, commercially available, rendering them
ideal as amination reagents in organic reactions.6 In 2012, Wan and co-workers developed a method for the
synthesis of amides from aldehydes and N,N-disubstituted formamides under metal-free conditions.7
Meanwhile, reactions of N,N-disubstituted formamides with alcohols8 or acids,9 which furnished the
corresponding amides under oxidative conditions, have been reported. In 2014, Pan and co-workers reported
an elegant process for the copper-mediated synthesis of sulfonamides from thiols and formamides under air
atmosphere.10 In view of the above, we report herein a method for the formation of sulfonamides by
oxidative amination of sodium sulfinates with N-substituted formamides. To the best of our knowledge, the
synthesis of sulfonamides from sodium sulfinates and formamides has not been reported.
Previous work
O
a)
R
OH
or
O
H
R
N
catalyst
oxidant
O
R
3
R
N
3
O
+
R
2
R
R
R
H
2
or
OH
R
b)
2
O
S
CuCl, Cu(OAc)
cinnamic acid
SH
2
N
O
R
3
N
R
2
R
3
+
O
H
R
R
This work
Scheme 1. Reported and designed routes for amination of sodium sulfinate.
KOt-Bu (4.0 equiv), 50 ¡ãC,
1).
R
2
O
R
N
ONa
3
CH CN, 30 min
3
O
N
+
S
S
R
3
Results and Discussion
R
1
O
H
R
2
R
1
NIS (2.0 equiv), 50 ¡ãC,
2).
O
CH CN, 12 h
3
2

We initially chose N,N-dimethylformamide 1a and sodium p-tolylsulfinate 2a as the substrates to test the
reaction. As shown in Table 1, this reaction proceeded via a sequential two-step process. First, 1a was added
to a base in a solvent at 50 °C over 15 min. Next, a mixture of 2a and an oxidant in a solvent was added
dropwise at 50 °C. The mixture was stirred at 50 °C for 12 h. Various bases were tested for the proposed
reaction using 2.0 equiv. of N-iodosuccinimide (NIS) as the oxidant, in CH3CN (Table 1, entries 1-9). The
desired product 3a was obtained in 68% yield when KO-t-Bu was used as the base (entry 9). Other bases
such as KOH, K2CO3, CH3COONa, NaH, CH3Ona, and C2H5ONa proved inactive (entries 1-7). The product
yield was improved to 81% upon increasing the amount of KO-t-Bu to 4.0 equiv. (entry 10). Screening of
different solvents revealed that CH3CN was the best medium for this conversion (entries 10-16). Extensive
screening revealed that the reaction temperature affected the reaction, with lower yields obtained at 80 °C
and 25 °C (entries 17 and 18). The yield of 3a decreased to 65% in the presence of 1.0 equiv. of NIS (entry
19). Attempts to use alternative oxidants such as I2 and N-bromobutanimide (NBS) proved less efficient,
affording 3a in lower yields (entries 20 and 21).
Table 1. Optimization of reaction conditions.a
O
O
N
1) base, solvent, 50 °C, 30 min
S
H
N
O
2) sodium p-tolylsulfinate (2a), oxidant
solvent, 50 °C, 12 h
1a
3a
Yield
(%)
0
Entry
Base (equiv)
oxidant
Solvent
1
2
KOH (3.0)
NIS
NIS
CH3CN
CH3CN
K2CO3 (3.0)
0
3
CH3COONa (3.0)
NIS
CH3CN
0
4
5
HCOONa (3.0)
NaH (3.0)
NIS
NIS
NIS
NIS
NIS
NIS
NIS
NIS
NIS
NIS
NIS
NIS
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
EtOH
trace
trace
trace
trace
15
6
CHONa (3.0)
C2H5ONa (3.0)
NaO-t-Bu (3.0)
KO-t-Bu (3.0)
KO-t-Bu (4.0)
KO-t-Bu (4.0)
KO-t-Bu (4.0)
KO-t-Bu (4.0)
KO-t-Bu (4.0)
KO-t-Bu (4.0)
KO-t-Bu (4.0)
7
8
9
68
10
11
12
13
14
13
14
81
36
PhMe
70
C6H5Cl
CH2Cl2
DCE
42
20
64
NIS
xylene
trace
3

15
16
17
18
19
20
21
KO-t-Bu (4.0)
KO-t-Bu (4.0)
KO-t-Bu (4.0)
KO-t-Bu (4.0)
KO-t-Bu (4.0)
KO-t-Bu (4.0)
KO-t-Bu (4.0)
NIS
NIS
NIS
NIS
NIS
I2
CH3OH
isopropanol
CH3CN
38
27
54b
73c
65d
74
CH3CN
CH3CN
CH3CN
NBS
CH3CN
51
a Reaction conditions: 1) 1a (4.0 equiv.), base (x equiv), solvent (2 mL), 50 °C, 30 min. 2) 2a (1.0 mmol), oxidant (2.0
equiv), solvent (2 mL), 50 °C, 12 h, Schlenk tube under air.
b The mixture was stirred at 80 °C.
c The mixture was stirred at 25 °C.
d 1.0 equiv of NIS was used.
This optimized protocol could be applied to the coupling of 1a with a broad range of sodium sulfinates
(Table 2). Sodium benzenesulfinate afforded the product in 85% yield (3b). o-Substituted sodium
benzenesulfinates gave a lower yield, which might be explained by the steric hindrance at the ortho-position
(3c). Halogen groups on the aromatic ring of the sodium benzenesulfinates were well tolerated in the
reaction, affording the desired product in moderate yields (3d-3g). The reactions of sodium arenesulfinates
bearing electron-donating or electron -withdrawing groups at the para-position of the aryl ring afforded the
corresponding products 3h−3k in good yields (65−85%). However, a much lower yield of sulfonamide 3l
was obtained when 4-nitro-substituted benzenesulfinate was used. 1-Naphthyl sodium sulfinate and
2-naphthyl sodium sulfinate were also suitable reactants for this reaction and gave the corresponding
products 3n and 3o in 55% and 62% yield respectively. In addition, heterocyclic sodium sulfinates were
tolerated in this reaction, and the desired products were obtained in moderate yields (3p-3r).
Table 2. Reactions of various sodium sulfinates with DMF.a
4

KOt-Bu (4.0 equiv), 50 °C,
1).
2).
O
H
O
CH CN, 15min
3
N
N
S
R
ONa
O
NIS (2.0 equiv), 50 °C,
S
CH CN, 12 h
1a
3
3
R
O
2
O
S
O
S
O
O
S
N
N
N
N
S
O
O
O
O
I
3d, 28%
3c, 72%
3b, 85%
3a, 81%
O
S
O
S
O
S
O
S
N
N
N
N
O
O
O
O
O
Cl
F
Br
3h, 70%
3f, 45%
3g, 42%
3e, 45%
O
S
O
S
O
S
N
N
N
O
S
N
O
O
O
O
O
O
O N
F C
3
2
3j, 85%
3k, 76%
3l, 27%
3i, 65%
O
S
O
S
O
S
N
N
N
O
S
N
O
O
O
O
N
3p, 49%
3o, 62%
3m, 53%
3n, 55%
O
O
N
N
S
S
Cl
O
O
S
S
Cl
3r, 45%
3q, 58%
a Reaction conditions: 1a (4.0 equiv.), KO-t-Bu (4.0 equiv), CH3CN (2 mL), 50°C, 30 min. 2 (1.0 mmol), NIS (2.0 equiv),
CH3CN (1 mL), 50°C, 12 h, Schlenk tube under air.
A series of formamides were also examined to expand the synthetic utility of the protocol (Table 3).
N-Formylpiperidine was suitable for this transformation, giving products 4a and 4b in good yields. Various
substituted sodium arenesulfinates were reacted with N-acetylmorpholine, and the desired sulfonamides
5

4c-4g were obtained in satisfactory yields. N-Acetylmorpholine also smoothly react with sodium
thiophene-2-sulfinate to form the corresponding sulfonamide 4h. Sulfonamide 4i was obtained in lower
yield when N,N-diethylformamide was used, because of the larger steric hindrance on the nitrogen atom of
the formamide. Moreover, N-benzyl-N-methyl-formamide was a compatible substrate for this transformation
and provided the desired sulfonamide 4j in 70% yield.
Table 3. Reactions of N,N-disubstituted formamides with sodium sulfinates.a
R1
N
KOt-Bu (4.0 equiv), 50 °C,
CH3CN, 15min
1).
2).
O
H
R1
N
R2
O
S
R2
R
ONa
O
NIS (2.0 equiv), 50 °C,
S
CH3CN, 12 h
1
4
R
O
2
O
N S
O
O
O
N S
O
O
N S
O
4c, 91%
4b, 68%
4a, 77%
O
O
N S
O
O
N S
O
NO2
O
O
O
N S
O
O
4f, 67%
4e, 88%
4d, 78%
O
N S
O
O
O
S
O
O
N S
N
S
O
O
4i, 24%
4g, 85%
4h, 82%
O
N S
O
4j, 70%
a Reaction conditions: 1 (4.0 equiv.), KO-t-Bu (4.0 equiv), CH3CN (2 mL), 50℃, 30 min. 2 (1.0 mmol), NIS (2.0 equiv),
CH3CN (1 mL), 50℃, 12 h, Schlenk tube under air.
To gain further insights into the reaction mechanism, several control experiments were performed. When
radical scavengers BHT (2,6-di-tert-butyl-4-methylphenol) and TEMPO (2,2,6,6-tetramethylpiperidine
1-oxyl) were added to the reaction system, the desired product 3a was obtained in 29% yield and in trace
amounts, respectively (Scheme 2, eq 1). These results implied that a radical step is involved in the reaction.
Compound 3a was obtained in 72% yield when N,N-dimethylformamide 1a was changed to dimethylamine
5 (Scheme 2, eq 2). The desired product was not detected when the reaction was carried out without
6

KO-t-Bu (Scheme 2, eq 3). However, 5 was reacted with sodium 2a to form 3a in 86% yield in the
absence of KO-t-Bu (Scheme 2, eq 4). These results indicated that the amine intermediate formed by the
decarbonylation of formamide and KO-t-Bu plays a key role in the decarbonylation process. Moreover, no
desired product was obtained when the reaction was carried out without NIS (Scheme 2, eq 5). When 2a was
replaced with freshly prepared p-toluenesulfonyl iodide 6, the reaction proceeded smoothly with
N,N-dimethylformamide 1a in the absence of NIS, affording the desired product in 50% yield (Scheme 2, eq
6). This result suggested sulfonyl iodide is another intermediate for this transformation.
On the basis of the results described above and from literature reports, we propose a possible reaction
pathway, as outlined in Scheme 3. Initially, formamide 1a is decarbonylated by KO-t-Bu to form amine A.11
Simultaneously, sodium sulfinate interacts with NIS to generate sulfonyl iodide 63r. Due to its instability, 6
easily undergoes homolysis to give a sulfonyl radical B and an iodine radical (I•).12 Finally, sulfonyl radical
B is attacked by amine A, leading to the desired sulfonamide 3a, with the concomitant formation of HI.
7

O
S
O
KOt-Bu (4.0 equiv), 50 °C,
1).
2)
N
CH CN, 15min
3
H
N
O
(1)
sodium p-tolylsulfinate (2a), NIS
(2.0 equiv), 50 °C, CH CN, 12 h
3
1a
3a
radical inhibitors (2.0 equiv)
BHT
TEMPO
29%
trace
KOt-Bu (4.0 equiv), 50 °C,
1)
2)
O
N
CH CN, 15min
S
3
H
N
O
(2)
sodium p-tolylsulfinate (2a), NIS
(2.0 equiv), 50 °C, CH CN, 12 h
3
5
3a
72%
O
ONa
O
O
S
S
N
NIS (2.0 equiv)
H
N
+
O
(3)
50 °C, CH CN, 12 h
3
1a
3a
2a
0%
O
S
ONa
O
N
NIS (2.0 equiv)
S
H
N
+
O
(4)
50 °C, CH CN, 12 h
3
5
3a
2a
86%
O
O
S
ONa
N
S
O
KOt-Bu (4.0 equiv)
O
+
(5)
H
N
1a
50 °C, CH CN, 12 h
3
3a
2a
0%
O
S
N
O
O
S
KOt-Bu (4.0 equiv)
I
O
+
(6)
H
N
1a
O
50 °C, CH CN, 12 h
3
3a
6
50%
Scheme 2. Control experiments.
O
S
ONa
O
NIS
S
I
O
2a
6
O
O
N
KOt-Bu
O
S
S
+
HN
+
I
O
H
N
O
A
B
CO
HI
3a
1a
Scheme 3. Proposed pathway for sulfonamide formation.
8

Conclusions
In conclusion, we have developed a protocol for KO-t-Bu mediated direct S–N bond formation from
sodium sulfinates and formamides. This protocol provides a simple and green approach for the preparation
of sulfonamide derivatives from sodium sulfinates and N,N-disubstituted formamides.
Acknowledgements
This work was supported by National Natural Science Foundation of China (21602159 and 81622043),
Public Welfare Science and Technology Project of Wenzhou (Y20160164), and Natural Science Foundation
of Zhejiang Province (LY17B020008).
References
1.
(a) Banerjee, M.; Poddar, A.; Mitra, G.; Surolia, A.; Owa, T.; Bhattacharyya, B. J Med Chem. 2005,
48, 547-555; (b) Scozzafava, A.; Owa, T.; Mastrolorenzo, A.; Supuran, C. T. Curr Med Chem. 2003,
10, 925-953; (c) Bano, S.; Javed, K.; Ahmad, S.; Rathish, I. G.; Singh, S.; Alam, M. S. Eur J Med
Chem. 2011, 46, 5763-5768.
2.
3.
(a) Sridhar, R.; Srinivas, B.; Kumar, V. P.; Narender, M.; Rao, K. R. Adv Synth Catal. 2007, 349,
1873-1876; (b) Harmata, M.; Zheng, P. G.; Huang, C. F.; Gomes, M. G.; Ying, W. J.; Ranyanil, K.
O.; Balan, G.; Calkins, N. L. J Org Chem. 2007, 72, 683-685.
For selected reviews and papers on the sulfonylation using sodium sulfinates, see: (a) Shaaban, S.;
Liang, S.; Liu, N. W.; Manolikakes, G. Org Biomol Chem. 2017, 15, 1946-1954; (b) Tang, X. D.;
Huang, L. B.; Xu, Y. L.; Yang, J. D.; Wu, W. Q.; Jiang, H. F. Angew Chem Int Ed. 2014, 53,
4205-4208; (c) Xiao, F. H.; Chen, H.; Xie, H.; Chen, S. Q.; Yang, L.; Deng, G. J. Org Lett. 2014, 16,
50-53; (d) Katrun, P.; Mueangkaew, C.; Pohmakotr, M.; Reutrakul, V.; Jaipetch, T.; Soorukram, D.;
Kuhakarn, C. J Org Chem. 2014, 79, 1778-1785; (e) Xu, Y. L.; Tang, X. D.; Hu, W. G.; Wu, W. Q.;
Jiang, H. F. Green Chem. 2014, 16, 3720-3723; (f) Meyer, A. U.; Jager, S.; Hari, D. P.; Konig, B.
Adv Synth Catal. 2015, 357, 2050-2054; (g) Taniguchi, N. J Org Chem. 2015, 80, 7797-7802; (h)
Du, B. N.; Qian, P.; Wang, Y.; Mei, H. B.; Han, J. L.; Pan, Y. Org Lett. 2016, 18, 4144-4147; (i) Li,
W. Y.; Yin, G. X.; Huang, L.; Xiao, Y.; Fu, Z. M.; Xin, X.; Liu, F.; Li, Z. Z.; He, W. M. Green
Chem. 2016, 18, 4879-4883; (j) Yang, W. C.; Dai, P.; Luo, K.; Wu, L. Adv Synth Catal. 2016, 358,
3184-3190; (k) Sun, Y. D.; Abdukader, A.; Lu, D.; Zhang, H. Y.; Liu, C. J. Green Chem. 2017, 19,
1255-1258; (l) Wei, W.; Cui, H. H.; Yang, D. S.; Liu, X. X.; He, C. L.; Dai, S. C.; Wang, H. Org
Chem Front. 2017, 4, 26-30; (m) Zeng, K.; Chen, L.; Chen, Y.; Liu, Y. P.; Zhou, Y. B.; Au, C. T.;
Yin, S. F. Adv Synth Catal. 2017, 359, 841-847; (n) Wu, W. Q.; Yi, S. J.; Yu, Y.; Huang, W.; Jiang,
H. F. J Org Chem. 2017, 82, 1224-1230; (o) Liang, S.; Bolte, M.; Manolikakes, G. Chem Eur J.
2017, 23, 96-100; (p) Liang, S.; Manolikakes, G. Adv Synth Catal. 2016, 358, 2371-2378; (q) Liu, J.
D.; Yu, L.; Zhuang, S. B.; Gui, Q. W.; Chen, X.; Wang, W. D.; Tan, Z. Chem Commun. 2015, 51,
6418-6421; (r) Fu, L.; Bao, X.; Li, S.; Wang, L.; Liu, Z.; Chen, W.; Xia, Q.; Liang, G. Tetrahedron
2017, 73, 2504-2511.
9

4.
5.
Tang, X. D.; Huang, L. B.; Qi, C. R.; Wu, X.; Wu, W. Q.; Jiang, H. F. Chem Commun. 2013, 49,
6102-6104.
(a) Wei, W.; Liu, C. L.; Yang, D. S.; Wen, J. W.; You, J. M.; Wang, H. Adv Synth Catal. 2015, 357,
987-992; (b) Yang, K.; Ke, M. L.; Lin, Y. G.; Song, Q. L. Green Chem. 2015, 17, 1395-1399; (c)
Buathongjan, C.; Beukeaw, D.; Yotphan, S. Eur J Org Chem. 2015, 1575-1582; (d) Zhao, J. W.; Xu,
J. X.; Chen, J. X.; Wang, X. Q.; He, M. H. Rsc Advances 2014, 4, 64698-64701; (e) Jiang, Y. Y.;
Wang, Q. Q.; Liang, S.; Hu, L. M.; Little, R. D.; Zeng, C. C. J Org Chem. 2016, 81, 4713-4719; (f)
Pan, X. J.; Gao, J.; Liu, J.; Lai, J. Y.; Jiang, H. F.; Yuan, G. Q. Green Chem. 2015, 17, 1400-1403;
(g) Wu, S. X.; Zhang, Y. K.; Zhu, M.; Yan, J. Synlett 2016, 27, 2699-2704; (h) Parumala, S. K. R.;
Peddinti, R. K. Tetrahedron Lett. 2016, 57, 1232-1235.
6.
For selected recent examples of formamides as amination reagents, see: (a) He, Y. M.; Li, J.; Luo, S.;
Huang, J. B.; Zhu, Q. Chem Commun. 2016, 52, 8444-8447; (b) Wang, J. A.; Hou, J. T.; Wen, J.;
Zhang, J.; Yu, X. Q. Chem Commun. 2011, 47, 3652-3654; (c) Li, Y. M.; Xie, Y. S.; Zhang, R.; Jin,
K.; Wang, X. N.; Duan, C. Y. J Org Chem. 2011, 76, 5444-5449; (d) Hu, C. X.; Yan, X. F.; Zhou, X.
G.; Li, Z. K. Org Biomol Chem. 2013, 11, 8179-8182; (e) Wang, H.; Guo, L. N.; Duan, X. H. Org
Biomol Chem. 2013, 11, 4573-4576; (f) Zhao, Q.; Miao, T.; Zhang, X. B.; Zhou, W.; Wang, L. Org
Biomol Chem. 2013, 11, 1867-1873; (g) Kumar, S.; Vanjari, R.; Guntreddi, T.; Singh, K. N.
Tetrahedron 2016, 72, 2012-2017; (h) Bao, Y. S.; Wang, L. L.; Jia, M. L.; Xu, A. J.; Agula, B.;
Baiyin, M. H.; Zhaorigetu, B. Green Chem. 2016, 18, 3808-3814; (i) Zhang, M. Z.; Guo, Q. H.;
Sheng, W. B.; Guo, C. C. Adv Synth Catal. 2015, 357, 2855-2861; (j) Gao, L. F.; Tang, H. M.;
Wang, Z. Y. Chem Commun. 2014, 50, 4085-4088.
7.
Liu, Z. J.; Zhang, J.; Chen, S. L.; Shi, E. B.; Xu, Y.; Wan, X. B. Angew Chem Int Ed. 2012, 51,
3231-3235.
8.
Xu, K.; Hu, Y. B.; Zhang, S.; Zha, Z. G.; Wang, Z. Y. Chem Eur J. 2012, 18, 9793-9797.
Xie, Y. X.; Song, R. J.; Yang, X. H.; Xiang, J. N.; Li, J. H. Eur J Org Chem. 2013, 2013, 5737-5742.
Huang, X.; Wang, J. C.; Ni, Z. Q.; Wang, S. C.; Pan, Y. J. Chem Commun. 2014, 50, 4582-4584.
9.
10.
11
Perrin, D. D.; Armarego, W. L. F. Purification of Laboratory Chemicals, 3rd edn., Pergamon, Oxford,
1988.
12.
Katrun, P.; Mueangkaew, C.; Pohmakotr, M.; Reutrakul, V.; Jaipetch, T.; Soorukram, D.; Kuhakarn,
C. J Org Chem. 2014, 79, 1778-1785.
10