RSC Advances
Communication
591; (d) T.-P. Loh and G.-L. Chua, Chem. Commun., 2006,
2739; (e) C. G. Frost and J. P. Hartley, Mini-Rev. Org. Chem.,
2004, 1, 1; (f) J. Podlech and T. C. Maier, Synthesis, 2003,
633; (g) F. Fringuelli, O. Piermatti, F. Pizzo and L. Vaccaro,
Curr. Org. Chem., 2003, 7, 1661; (h) K. K. Chauhan and
C. G. Frost, J. Chem. Soc., Perkin Trans. 1, 2000, 3015.
Fig. 1 Deuterium exchange experiments.
2
For representative recent examples on various applications
of trivalent indium as Lewis acid catalyst, see: (a)
S. A. Ruider, S. M u¨ ller and E. M. Carreira, Angew. Chem.,
Int. Ed., 2013, 52, 11908; (b) P. Liu, Y.-m. Pan, K. Hu,
X.-c. Huang, Y. Liang and H.-s. Wang, Tetrahedron, 2013,
69, 7925; (c) Y.-l. Xu, Y.-m. Pan, P. Liu, H.-s. Wang,
X.-y. Tian and G.-f. Su, J. Org. Chem., 2012, 77, 3557; (d)
J.-F. Zhao, B.-H. Tan and T.-P. Loh, Chem. Sci., 2011, 2,
349; (e) T. Tsuchimoto and M. Kanbara, Org. Lett., 2011,
13, 912; (f) Y. Kuninobu, T. Tatsuzaki, T. Matsuki and
K. Takai, J. Org. Chem., 2011, 76, 7005; (g) Y. Zhang, P. Li,
M. Wang and L. Wang, J. Org. Chem., 2009, 74, 4364; (h)
J.-F. Zhao, H.-Y. Tsui, P.-J. Wu, J. Lu and T.-P. Loh, J. Am.
Chem. Soc., 2008, 130, 16492; (i) H.-B. Zhang, L. Liu,
Y.-J. Chen, D. Wang and C.-J. Li, Adv. Synth. Catal., 2006,
348, 229; (j) M. Yasuda, T. Somyo and A. Baba, Angew.
Chem., Int. Ed., 2006, 45, 793.
Fig. 2 Proposed reaction mechanism.
3
(a) M. C. Haibach and D. Seidel, Angew. Chem., Int. Ed., 2014,
53, 5010; (b) B. Peng and N. Maulide, Chem.–Eur. J., 2013, 19,
1
3274; (c) M. Tobisu and N. Chatani, Angew. Chem., Int. Ed.,
coordination of the indium Lewis acid to the N atom on the
substrates which effectively activates the C(sp )–H bonds
3
2006, 45, 1683.
4
5
(a) S. H. Cho, J. Y. Kim, J. Kwak and S. Chang, Chem. Soc.
Rev., 2011, 40, 5068; (b) P. Thansandote and M. Lautens,
Chem.–Eur. J., 2009, 15, 5874.
towards their cleavage. This subsequently leads to the forma-
tion of indium-enamide intermediates from which addition to
the carbonyl carbons of TFMKs proceed to give the intended
products.
For representative reviews, see: (a) X.-S. Zhang, K. Chen and
Z.-J. Shi, Chem. Sci., 2014, 5, 2146; (b) H. Tsurugi,
K. Yamamoto, H. Nagae, H. Kaneko and K. Mashima,
Dalton Trans., 2014, 43, 2331; (c) G. Yan, X. Wu and
M. Yang, Org. Biomol. Chem., 2013, 11, 5558; (d) R. Jazzar,
J. Hitce, A. Renaudat, J. Sofack-Kreutzer and O. Baudoin,
Chem.–Eur. J., 2010, 16, 2654; (e) K. Godula and D. Sames,
Science, 2006, 312, 67; (f) F. Kakiuchi and N. Chatani, Adv.
Synth. Catal., 2003, 345, 1077.
3
In conclusion, a simple In-catalyzed C(sp )–H functionali-
zation through direct benzylic addition under Lewis acid
catalysis was successfully developed. InCl was found to cata-
3
lytically promote the addition of benzylic C–H bonds in
2-methylazaarenes to the carbonyl carbons of TFMKs. This
protocol is highly efficient in which products of up to quanti-
tative yield could be obtained under mild conditions. In addi-
tion to the asymmetric variants, endeavors are also currently
3
6 For representative examples, see: (a) Z.-Q. Zhu, P. Bai and
Z.-Z. Huang, Org. Lett., 2014, 16, 4881; (b) F.-F. Wang,
C.-P. Luo, G. Deng and L. Yang, Green Chem., 2014, 16,
directed towards the development of In-catalyzed C(sp )–H
functionalization with other classes of alkylazaarenes and
electrophilic acceptors for the C–H addition.
2428; (c) D. Pi, K. Jiang, H. Zhou, Y. Sui, Y. Uozumi and
K. Zou, RSC Adv., 2014, 4, 57875; (d) Z. Jamal, Y.-C. Teo
and L.-K. Wong, Eur. J. Org. Chem., 2014, 7343; (e) Z. Jamal
and Y.-C. Teo, Synlett, 2014, 2049; (f) X. Wang, S.-y. Li,
Y.-m. Pan, H.-s. Wang, H. Liang, Z.-f. Chen and X.-h. Qin,
Org. Lett., 2014, 16, 580; (g) Y. Li, F. Guo, Z. Zha and
Z. Wang, Chem.–Asian J., 2013, 8, 534; (h) B.-T. Guan,
B. Wang, M. Nishiura and Z. Hou, Angew. Chem., Int. Ed.,
Acknowledgements
We would like to thank the National Institute of Education,
Nanyang Technological University for their generous nancial
support.
2
013, 52, 4418; (i) S.-J. Lou, D.-Q. Xu, D.-F. Shen,
Notes and references
Y.-F. Wang, Y.-K. Liu and Z.-Y. Xu, Chem. Commun., 2012,
48, 11993; (j) J.-Y. Liu, H.-Y. Niu, S. Wu, G.-R. Qu and
H.-M. Guo, Chem. Commun., 2012, 48, 9723; (k) H. Komai,
T. Yoshino, S. Matsunaga and M. Kanai, Synthesis, 2012,
2185; (l) J.-J. Jin, H.-Y. Niu, G.-R. Qu, H.-M. Guo and
J. S. Fossey, RSC Adv., 2012, 2, 5968; (m) B. M. Trost,
1
For an overview on indium chemistry, see: (a) Z.-L. Shen,
S.-Y. Wang, Y.-K. Chok, Y.-H. Xu and T.-P. Loh, Chem. Rev.,
2012, 113, 271; (b) U. Schneider and S. Kobayashi, Acc.
Chem. Res., 2012, 45, 1331; (c) J. S. Yadav, A. Antony,
J. George and B. V. Subba Reddy, Eur. J. Org. Chem., 2010,
26952 | RSC Adv., 2015, 5, 26949–26953
This journal is © The Royal Society of Chemistry 2015