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DOI: 10.1039/C6CC01135G
Journal Name
COMMUNICATION
Lastly, it should be mentioned that the stannylation of 4-
chlorobenzonitrile also afforded 3d in moderate yield (56%).
To gain insights into the reaction mechanism, we have
carried out a series of control experiments (Table 2). When the
reaction of ethyl 4-iodobenzoate 1f with the (SnMe3)2 (2) was
run under the standard conditions, 10% of hydrodeiodination
product 4f was formed accompanying the stannylation product
3f (83% 1H NMR yield) (entry 1). In the absence of light, no
conversion was observed at room temperature (entry 2).
However, small amount of 3a (12%) could be formed when the
dark reaction was performed at 70 oC overnight (entry 3).
When 1.5 equiv of TEMPO (2,2,6,6-tetramethylpiperidine-1-
oxyl) was added in the reaction, the yield of 3f dropped to 17%
(entry 4). The amount of the side product 4f was significantly
increased when 9,10-dihydroanthracene (1.5 equiv) was added
(entry 5). When the photolytic reaction was stopped at 10 min
immediately before workup, 82% of conversion and 70% of 3f
were observed (entry 6). In contrast, if the 10 min irradiation
was followed by another 50 min dark reaction, the outcome
was essentially same to the result of the standard condition
(entry 7 vs. entry 1). Finally, a dark reaction using 10% of AIBN
Scheme 3 Proposed reaction mechanism
In conclusion, we have designed and developed an efficient
photo-induced transition-metal-free stannylation reaction to
synthesize aryl trimethylstannanes from various aryl and
heteroaryl halides. In comparison with the previous methods,
this reaction features mild reaction conditions, broad
functional group tolerance, generally good yields and simple
experimental operation. Further investigations on the reaction
mechanism and expansion of the substrate scope are currently
ongoing.
We are grateful for financial support by the National Science
Foundation of China (No. 21472146), the Department of Science
and Technology of Shaanxi Province (No. 2015KJXX-02) and the
Ministry of Science and Technology of PRC (973 program for young
scientists, No. 2014CB548200).
as a radical initiator could also promote the formation of 3a
albeit in lower yield (entry 8).
,
Table 2 Control experiments for preliminary mechanistic studya
Notes and references
1
(a) J. K. Stille, Angew. Chem. Int. Ed., 1986, 25, 508; (b) V.
Farina, V. Krishnamurthy, W. J. Scott, Org. React., 1997, 50
1; (c) J. Hassan, M. Sevignon, C. Gozzi, E. Schulz and M.
Lemaire, Chem. Rev., 2002, 102, 1359; (d) P. Espinet, A. M.
Echavarren, Angew. Chem. Int. Ed., 2004, 43, 4704; (e) C.
Cordovilla, C. Bartolome, J. M. Martinez-Ilarduya and P.
Ent
ry
1
Additive
Conver-
sion [%]
100
0
Yield of
3f [%]
85
Yield of
Light
,
(equiv)
4f [%]
10
0
on
off
-
2
3b
-
0
off
-
15
12
3
Espinet, ACS Catal., 2015, 5, 3040.
4
on
TEMPO (1.5)
79
17
9
2
For selected examples of Stille coupling in total synthesis of
natural products, see: (a) K. C. Nicolaou, Y. He, F.
Roschangar, N. P. King, D. Vourloumis and T. Li, Angew.
Chem. Int. Ed., 1998, 37, 84; (b) P. Li, J. Li, F. Arikan, W.
Ahlbrecht, M. Dieckmann and D. Menche, J. Am. Chem. Soc.,
2009, 131, 11678; (c) D. Mailhol, J. Willwacher, N. Kausch-
Busies, E. E. Rubitski, Z. Sobol, M. Schuler, M.-H. Lam, S.
Musto, F. Loganzo, A. Maderna and A. Fürstner, J. Am. Chem.
Soc., 2014, 136, 15719; (d) J. Li, P. Yang, M. Yao, J. Deng and
A. Li, J. Am. Chem. Soc., 2014, 136, 16477.
(a) J. A. Ragan, J. W. Raggon, P. D. Hill, B. P. Jones, R. E.
McDermott, M. J. Munchhof, M. A. Marx, J. M. Casavant, B.
A. Cooper, J. L. Doty and Y. Lu, Org. Proc. Res. Dev., 2003, 7,
676. (b) N. Yasuda, C. Yang, K. M. Wells, M. S. Jensen and D.
L. Hughes, Tetrahedron Lett., 1999, 40, 427.
For selected references, see: (a) C. M. Amb, S. Chen, K. R.
Graham, J. Subbiah, C. E. Small, F. So and J. R. Reynolds, J.
Am. Chem. Soc., 2011, 133, 10062; (b) S. C. Price, A. C. Stuart,
L. Yang, H. Zhou and W. You, J. Am. Chem. Soc., 2011, 133
4625; (c) D. Qian, W. Ma, Z. Li, X. Guo, S. Zhang, L. Ye, H. Ade,
Z. Tan and J. Hou, J. Am. Chem. Soc., 2013, 135, 8464.
For selected examples, see: (a) P. Y. S. Lam, G. Vincent, D.
Bonne, C and G. Clark, Tetrahedron Lett., 2002, 43, 3091; (b)
T. Furuya, A. E. Strom and T. Ritter, J. Am. Chem. Soc., 2009,
131, 1662; (c) P. Tang, T. Furuya and T. Ritter, J. Am. Chem.
Soc., 2010, 132, 12150; (d) C. Huang, T. Liang, S. Harada, E.
Lee, T. Ritter, J. Am. Chem. Soc., 2011, 133, 13308.
5
on
DHA (1.5)
100
82
47
50
9
6c
7d
8
on
-
70
on/off
-
100
85
8
off
AIBN (0.1)
100
65
32
aReactions were run for 1 h unless otherwise stated, yields were determined by 1H
b
NMR spectroscopic analysis with 1,3,5-trimethoxybenzene as an internal standard;
The reaction was run at 70 oC for 12 h in dark; cThe reaction mixture was irradiated
under UV light for 10 min immediately before workup; dThe reaction mixture was
irradiated under UV light for 10 min and then stirred in dark for another 50 min before
workup; DIPEA: N,N-Diisopropylethylamine; DHA: 9,10-dihydroanthracene; TEMPO:
(2,2,6,6-tetramethylpiperidin-1-yl)oxyl; AIBN: azobisisobutyronitrile.
3
4
Based on the experimental results and related reports on
photolytic reactions of aryl iodides,[14] we propose a radical
reaction pathway involving a photolytically generated aryl
radical as the possible mechanism (Scheme 3a). Thus, the
excited state of the aryl iodide may be generated by UV
irradiation and then undergo homolytic C-I bond cleavage to
form the aryl radical and an iodine atom. The aryl radical may
,
5
react with hexamethyldistannane
3
(2) to produce the
stannylation product and a trimethylstannyl radical, which
may be trapped by the iodine atom to form trimethyltin iodide.
An alternative radical chain pathway can not be excluded,
wherein a trimethylstannyl radical might react with aryl iodide
to generate another aryl radical (Scheme 3b).
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