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Scheme 3 Asymmetric cyanation of aromatic aldehydes under aging
conditions.
4 A. Baeza, J. Casas, C. Najera, J. M. Sansano and J. M. Saa,
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Angew. Chem., Int. Ed., 2003, 42, 3143; Y. Abiko, N. Yamagiwa,
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acetone cyanohydrin, see: S. Nanda, Y. Kato and Y. Asano,
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9 For examples of enantioselective synthesis of non-protected cyano-
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Fig. 2 Time dependence of conversion in the presence of 1 mol% of
complex 1 after aging for 0 h (J), 2 h (K) and 6 h (n). Each data
point is an average of at least four runs.
11 With enzymatic methods, high enantioselectivity can be obtained
at room temperature. For reviews, see: F. Effenberger, Angew.
with vanadium cyanide intramolecularly to produce enantio-
enriched cyanohydrin.
Chem., Int. Ed. Engl., 1994, 33, 1555; H. Groger, Adv. Synth.
Catal., 2001, 343, 547. See also ref. 2.
¨
In summary, we achieved the highly enantioselective synthesis
of non-protected cyanohydrins at room temperature, which
was realized by the vanadium(salalen) catalysis with acetone
cyanohydrin as a cyanide source. Various aliphatic cyano-
hydrins were obtained in high yield with high enantioselectivity
ranging from 89 to 95% ee in the presence of only 0.2–0.4 mol%
of the catalyst. While aromatic aldehydes showed poor enantio-
selectivity under the conditions, high enantioselectivity could be
obtained under the reaction conditions with aging. Further
studies to clarify the reaction mechanism and other applications
of the vanadium catalysis are ongoing.
12 Selected examples of highly enantioselective synthesis of protected
cyanohydrins at ambient temperature, see: Y. N. Belokon’,
S. Caveda-Cepas, B. Green, N. S. Ikonnikov, V. N. Khrustalev,
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13 J. Takaki, H. Egami, K. Matsumoto, B. Saito and T. Katsuki,
Chem. Lett., 2008, 37, 502.
14 Vanadium(salen) complexes also catalyze asymmetric cyanation
using acetone cyanohydrin, see: A. Watanabe, K. Matsumoto,
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6229.
This work was supported by a Grant-in-Aid for Scientific
Research (Specially Promoted Research 18002011), and the
Global COE program ‘‘Science for Future Molecular Systems’’
from MEXT (Japan).
Notes and references
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2005, 11, 3849; F. Yang, S. Wei, C. Chen, P. Xi, L. Yang, J. Lan,
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16 Although acetone cyanohydrin used in this study contains a small
amount of acetone, the amount was constant in the absence of
complex 1.
17 In some instances using TMSCN, hydrogen cyanide generated
from TMSCN and protic reagents such as water and alcohols has
been reported to be the real cyanating agent. For an example, see
ref. 1.
1 J.-M. Brunel and I. P. Holms, Angew. Chem., Int. Ed., 2004, 43,
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and references cited therein.
2 A. Mori and S. Inoue, in Comprehensive Asymmetric Catalysis, ed.
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ꢀc
This journal is The Royal Society of Chemistry 2010
Chem. Commun., 2010, 46, 5787–5789 | 5789