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X. Wang, S.-K. Tian / Tetrahedron Letters 48 (2007) 6010–6013
cyanosilylation of ketones, and presumably a double-
activation mechanism is responsible for this catalysis.
On the one hand, the phosphonium cation may activate
ketone due to its Lewis acidity resulting from the pres-
1273; (p) Kano, T.; Sasaki, K.; Konishi, T.; Mii, H.;
Maruoka, K. Tetrahedron Lett. 2006, 47, 4615; (q) Suzuki,
Y.; Bakar, A. M. D.; Muramatsu, K.; Sato, M. Tetrahedron
2
006, 62, 4227; (r) Liu, X.; Qin, B.; Zhou, X.; He, B.; Feng,
6
a
X. J. Am. Chem. Soc. 2005, 127, 12224; (s) Fuerst, D. E.;
Jacobsen, E. N. J. Am. Chem. Soc. 2005, 127, 8964; (t) He,
B.; Li, Y.; Feng, X.; Zhang, G. Synlett 2004, 1776; (u)
C o´ rdoba, R.; Plumet, J. Tetrahedron Lett. 2003, 44, 6157;
ence of 3d orbitals. On the other hand, the counterion,
À
Cl , has been demonstrated by Ohkuma and co-workers
8
to be able to activate nucleophile TMSCN. The activa-
tion of TMSCN by benzyltriphenylphosphonium chlo-
ride was evidenced by the appearance of a new
(
v) Amurrio, I.; C o´ rdoba, R.; Cs a´ k y¨ , A. G.; Plumet, J.
Tetrahedron 2004, 60, 10521; (w) Blanrue, A.; Wilhelm, R.
Synlett 2004, 2621; (x) Miura, T.; Masaki, Y. J. Chem. Soc.,
Perkin Trans. 1 1995, 2155; (y) Miura, T.; Masaki, Y. J.
Chem. Soc., Perkin Trans. 1 1994, 1659.
. For the organocatalysis using alkyl cyanoformate as a
cyanide source, see: (a) Berthiaume, D.; Poirier, D. Tetra-
hedron 2000, 56, 5995; (b) Deardorff, D. R.; Taniguchi, C.
M.; Tafti, S. A.; Kim, H. Y.; Choi, S. Y.; Downey, K. J.;
Nguyen, T. V. J. Org. Chem. 2001, 66, 7191; (c) Tian, S.-K.;
Deng, L. J. Am. Chem. Soc. 2001, 123, 6195; (d) Tian,
S.-K.; Deng, L. Tetrahedron 2006, 62, 11320; (e) Poirier, D.;
Berthiaume, D.; Boivin, R. P. Synlett 1999, 1423.
À1
cyanide stretching band at 2254 cm , different from
À1
that for TMSCN (2190 cm
)
and TMSN = C
2088 cm ), in the IR spectrum of the 1:1 mixture.
À1
9
(
3
Since it is necessary for both phosphonium cation and
À
Cl to be dissociated from each other before the effective
activation of ketone and TMSCN, respectively, the
decent Lewis acidity of phosphonium cation seems to
be essential for the phosphonium salt to efficiently
practice double activation.
In summary, benzyltriphenylphosphonium chloride was
identified as a highly effective organocatalyst to promote
the cyanosilylation of a wide variety of unconjugated
and conjugated, acyclic and cyclic ketones. This proto-
col not only presents a new organocatalytic synthesis
of cyanohydrin silyl ethers, but also adds a synthetically
useful entry into the catalysis with phosphonium salts.
Further development of its asymmetric variant is
ongoing.
4. For recent reviews, see: (a) Achard, T. R. J.; Clutterbuck,
L. A.; North, M. Synlett 2005, 1828; (b) Kanai, M.; Kato,
N.; Ichikawa, E.; Shibasaki, M. Synlett 2005, 1491; (c)
Chen, F.-X.; Feng, X. Synlett 2005, 892; (d) Brunel, J.-M.;
Holmes, I. P. Angew. Chem., Int. Ed. 2004, 43, 2752; (e)
North, M. Tetrahedron: Asymmetry 2003, 14, 147; (f)
Gregory, R. J. H. Chem. Rev. 1999, 99, 3649.
5
. For some of the recent examples, see: (a) Xiong, Y.; Huang,
X.; Gou, S.; Huang, J.; Wen, Y.; Feng, X. Adv. Synth.
Catal. 2006, 348, 538; (b) Iwanami, K.; Aoyagi, M.;
Oriyama, T. Tetrahedron Lett. 2006, 47, 4741; (c) Li, Q.;
Liu, X.; Wang, J.; Shen, K.; Feng, X. Tetrahedron Lett.
2006, 47, 4011; (d) Khan, N. H.; Agrawal, S.; Kureshy, R.
I.; Abdi, S. H. R.; Mayani, V. J.; Jasra, R. V. Tetrahedron:
Asymmetry 2006, 17, 2659; (e) Kim, S. S.; Lee, S. H.; Kwak,
J. M. Tetrahedron: Asymmetry 2006, 17, 1165; (f) Moreno,
R. M.; Rosol, M.; Moyano, A. Tetrahedron: Asymmetry
Acknowledgments
We are grateful for the financial support from the
National Natural Science Foundation of China (No.
2
0672105) and the University of Science and Techno-
2
006, 17, 1089; (g) Rodr ´ı guez, B.; Past o´ , M.; Jimeno, C.;
logy of China.
Peric a` s, M. A. Tetrahedron: Asymmetry 2006, 17, 151; (h)
Kim, S. S.; Kwak, J. M. Tetrahedron 2006, 62, 49; (i)
Belokon, Y. N.; Maleev, V. I.; North, M.; Usanov, D. L.
Chem. Commun. 2006, 4614; (j) Belokon, Y. N.; Ishibashi,
E.; Nomura, H.; North, M. Chem. Commun. 2006, 1775; (k)
Gou, S.; Chen, X.; Xiong, Y.; Feng, X. J. Org. Chem. 2006,
71, 5732; (l) Baeza, A.; Casas, J.; N a´ jera, C.; Sansano, J.;
Sa a´ , J. M. Eur. J. Org. Chem. 2006, 1949; (m) Iwanami, K.;
Aoyagi, M.; Oriyama, T. Tetrahedron Lett. 2005, 46, 7487;
(n) Baeza, A.; N a´ jera, C.; Sansano, J. M.; Sa a´ , J. M.
Tetrahedron: Asymmetry 2005, 16, 2385; (o) Kurono, N.;
Yamaguchi, M.; Suzuki, K.; Ohkuma, T. J. Org. Chem.
2005, 70, 6530; (p) Ryu, D. H.; Corey, E. J. J. Am. Chem.
Soc. 2005, 127, 5384; (q) Hatano, M.; Ikeno, T.; Miyamoto,
T.; Ishihara, K. J. Am. Chem. Soc. 2005, 127, 10776; (r)
Lundgren, S.; Wingstrand, E.; Penhoat, M.; Moberg, C. J.
Am. Chem. Soc. 2005, 127, 11592; (s) Yamagiwa, N.; Tian,
J.; Matsunaga, S.; Shibasaki, M. J. Am. Chem. Soc. 2005,
127, 3413; (t) Qin, Y.-C.; Liu, L.; Pu, L. Org. Lett. 2005, 7,
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Org. Chem. 2004, 69, 7910; (v) Ryu, D. H.; Corey, E. J. J.
Am. Chem. Soc. 2004, 126, 8106; (w) Chen, F.-X.; Liu, X.;
Qin, B.; Zhou, H.; Feng, X.; Zhang, G. Synthesis 2004,
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C.-W.; Yang, C.-T.; Hwang, D.-R. Tetrahedron 2004, 60,
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(
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