Communication
ChemComm
We are grateful for the grants from the NSFC (No. 21432003)
and Fundamental Research Funds for the Central Universities
(lzujbky-2018-k09).
Conflicts of interest
There are no conflicts to declare.
Notes and references
1 For reviews, see: (a) K. H. Jensen and M. S. Sigman, Org. Biomol.
Chem., 2008, 6, 4083; (b) R. Giri and S. KC, J. Org. Chem., 2018,
83, 3013; (c) J. Derosa, V. T. Tran, V. A. van der Puyl and K. M. Engle,
Aldrichimica Acta, 2018, 51, 21.
Scheme 7 Mechanistic studies.
2 (a) B. Shrestha, P. Basnet, R. K. Dhungana, S. KC, S. Thapa, J. M. Sears
and R. Giri, J. Am. Chem. Soc., 2017, 139, 10653; (b) P. Gao, L.-A. Chen
and M. K. Brown, J. Am. Chem. Soc., 2018, 140, 10653; (c) J. Derosa,
R. Kleinmans, V. T. Tran, M. K. Karunananda, S. R. Wisniewski,
M. D. Eastgate and K. M. Engle, J. Am. Chem. Soc., 2018, 140, 17878;
(d) P. Basnet, S. KC, R. K. Dhungana, B. Shrestha, T. J. Boyle and
R. Giri, J. Am. Chem. Soc., 2018, 140, 15586; (e) K. B. Urkalan and
M. S. Sigman, Angew. Chem., Int. Ed., 2009, 48, 3146; ( f ) Z. Kuang,
K. Yang and Q. Song, Org. Chem. Front., 2017, 4, 1224.
3 (a) F. Wang, D. Wang, X. Mu, P. Chen and G. Liu, J. Am. Chem. Soc.,
2014, 136, 10202; (b) L. Wu, F. Wang, X. Wan, D. Wang, P. Chen and
G. Liu, J. Am. Chem. Soc., 2017, 139, 2904; (c) J. Terao, F. Bando and
N. Kambe, Chem. Commun., 2009, 7336; (d) X.-H. Ouyang, R.-J. Song,
M. Hu, Y. Yang and J.-H. Li, Angew. Chem., Int. Ed., 2016, 55, 3187;
(e) Y.-T. He, L.-H. Li, Y.-F. Yang, Z.-Z. Zhou, H.-L. Hua, X.-Y. Liu and
Y.-M. Liang, Org. Lett., 2014, 16, 270; ( f ) M. Li, J. Yang, X.-H. Ouyang,
Y. Yang, M. Hu, R.-J. Song and J.-H. Li, J. Org. Chem., 2016, 81, 7148;
(g) X. Yong, Y.-F. Han, Y. Li, R.-J. Song and J.-H. Li, Chem. Commun.,
2018, 54, 12816; (h) X.-H. Ouyang, M. Hu, R.-J. Song and J.-H. Li, Chem.
Commun., 2018, 54, 12345; (i) T. Qin, J. Cornella, C. Li, L. R. Malins,
J. T. Edwards, S. Kawamura, B. D. Maxwell, M. D. Eastgate and
P. S. Baran, Science, 2016, 352, 801; ( j) J.-W. Gu, Q.-Q. Min, L.-C. Yu
and X. Zhang, Angew. Chem., Int. Ed., 2016, 55, 12270; (k) W. Sha,
L. Deng, S. Ni, H. Mei, J. Han and Y. Pan, ACS Catal., 2018, 8, 7489.
Scheme 8 Proposed mechanism.
In this reaction, the tertiary amine could either act as a basic
additive or serve as a single electron reductant. To clarify this issue,
several control experiments were carried out (Scheme 7, eqn (1)).
When t-BuOLi was used instead of DIPEA under standard reac-
tion conditions, the reaction proceeded smoothly and product
3aa was obtained in 43% yield. The result indicated that DIPEA
may only act as base, rather than a single electron reductant.
Addition of BHT (butylated hydroxytoluene, 4.0 equivalents) led to
a dramatic decrease of the yield to 33% (eqn (2)). Furthermore, a
radical clock experiment via 6-bromo-1-hexene 2n was performed
and led to the formation of cyclization product 3an (eqn (3)).
According to our mechanistic studies and previous reports,6,8,9
a possible mechanism is proposed in Scheme 8. A rapid ligand
exchange of CuIX and TMSCN provided CuCN and TMSX.11 Under
UV light irradiation, CuCN was excited to its excited-state CuCN* (B).
The single electron-transfer process between B and alkyl halide
(BrÀ or IÀ) furnished a Cu(II)-cyanide adduct [CuII(CN)X] (C) and an
´
´
4 (a) A. Garcıa-Domınguez, Z. Li and C. Nevado, J. Am. Chem. Soc.,
2017, 139, 6835; (b) S. KC, R. K. Dhungana, B. Shrestha, S. Thapa,
N. Khanal, P. Basnet, R. W. Lebrun and R. Giri, J. Am. Chem. Soc.,
2018, 140, 9801.
5 (a) M. Mitani, M. Nakayama and K. Koyama, Tetrahedron Lett., 1980,
21, 4457; (b) M. Mitani, I. Kato and K. Koyama, J. Am. Chem. Soc.,
1983, 105, 6719.
6 T. S. Ratani, S. Bachman, G. C. Fu and J. C. Peters, J. Am. Chem. Soc.,
2015, 137, 13902.
7 Four 25 W UVC bulbs were used, which can be purchased from a
supermarket (B$9 each).
8 (a) F. Wang, D. Wang, X. Wan, L. Wu, P. Chen and G. Liu, J. Am.
Chem. Soc., 2016, 138, 15547; (b) W. Zhang, F. Wang, S. D. McCann,
D. Wang, P. Chen, S. S. Stahl and G. Liu, Science, 2016, 353, 1014;
(c) D. Wang, F. Wang, P. Chen, Z. Lin and G. Liu, Angew. Chem., Int.
Ed., 2017, 56, 2054; (d) D. Wang, N. Zhu, P. Chen, Z. Lin and G. Liu,
J. Am. Chem. Soc., 2017, 139, 15632; (e) F. Wang, D. Wang, Y. Zhou,
L. Liang, R. Lu, P. Chen, Z. Lin and G. Liu, Angew. Chem., Int. Ed.,
2018, 57, 7140; ( f ) S. Yang, L. Wang, H. Zhang, C. Liu, L. Zhang,
X. Wang, G. Zhang, Y. Li and Q. Zhang, ACS Catal., 2019, 9, 716.
9 (a) Q. Guo, M. Wang, Y. Wang, Z. Xu and R. Wang, Chem. Commun.,
2017, 53, 12317; (b) H. Liu, Q. Guo, C. Chen, M. Wang and Z. Xu,
Org. Chem. Front., 2018, 5, 1522.
10 (a) J. Cossy, J.-L. Ranaivosata and V. Bellosta, Tetrahedron Lett., 1994,
35, 8161; (b) P. J. Kropp and R. L. Adkins, J. Am. Chem. Soc., 1991,
113, 2709.
11 We attempted to directly use CuCN as the catalyst in the reaction.
However, CuCN hardly dissolved in CF3CH2OH.
ꢀ
ꢀ
alkyl radical R. R then attacked the electron-deficient alkene
to generate radical intermediate D, which next combined with
C to provide the nitrile and regenerate the CuIX catalyst.6 The
unstable species TMSX underwent rapid hydrolysis and was
trapped by DIPEA, which promoted a complete conversion.12,13
In summary, we have described a novel copper-catalyzed and
photo-induced strategy for achieving the cyanoalkylation of
electron-deficient alkenes with alkyl bromides. A series of unac- 12 P. V. Pham, D. A. Nagib and D. W. C. MacMillan, Angew. Chem., Int.
Ed., 2011, 50, 6119.
13 The adduct of DIPEA with an acidic compound was isolated as a
tivated 11, 21, 31 alkyl bromides and a-carbonyl alkyl bromides
performed well under standard reaction conditions and provided
white precipitate after the reaction was complete. The NMR char-
the corresponding product 3 in good to excellent yields.
acterization of this adduct is presented in the ESI†.
Chem. Commun.
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