Research from the Ministry of Education, Culture, Science,
Sports, and Technology of Japan.
Notes and references
z A divacant silicodecatungstate, [g-SiW10O34(H2O)2]4ꢀ, gave 3a in
18% yield. The yield of 3a could be increased from 18% to 35% by
replacement of Si with Ge, in accord with the acid strength order
(Si > Ge) of H4[XW12O40].7
Scheme 1 Reaction of 1b with salicylaldehyde catalyzed by I.
y Kaneda and co-workers reported that calcium vanadate apatite can
act as an efficient heterogeneous catalyst for Knoevenagel condensa-
tion and that the TOF is 7917 hꢀ1 (based on surface vanadium).5a
z The reactions of 1d, 1e, and acetone (1f) with 2a were carried out
under the same reaction conditions as those of entry 3 in Table 1. The
reaction of 1d gave the corresponding a,b-unsaturated product in 28%
yield. The reactions of 1e and 1f did not proceed.
1 (a) M. T. Pope, in Comprehensive Coordination Chemistry II,
ed. J. A. McCleverty and T. J. Meyer, Elsevier Pergamon,
Amsterdam, 2004, vol. 4, pp. 635–678; (b) P. Mialane, A. Dolbecq
Scheme 2 Cyanosilylation of (a) n-hexanal and (b) acetophenone
with trimethylsilyl cyanide catalyzed by I.
and F. Secheresse, Chem. Commun., 2006, 3477; (c) A. Proust,
´
R. Thouvenot and P. Gouzerh, Chem. Commun., 2008, 1837;
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Int. Ed., 2010, 49, 1736.
that of 1c, while the pKa values of 1d (16.4) and 1e (17.2)
are lower than that (21.9) of 1c, suggesting the specific
reactivity of I for the active methylene compounds with cyano
groups.z POM I also showed high catalytic activity for reac-
tion of 1a with various aldehydes (Table 1, entries 4–8).
Reactions of benzaldehydes with electron-donating as well as
-withdrawing para-substituents (2b and 2c) proceeded to
afford the corresponding products in high yields (Table 1,
entries 4 and 5). Not only an aromatic but also an aliphatic
aldehyde (2d) gave an excellent yield of the corresponding
alkene (Table 1, entry 6). The reaction of aldehydes containing
a double bond and a heteroatom also proceeded selectively to
give the corresponding a,b-unsaturated compounds (Table 1,
entries 7 and 8). Notably, ketones 2g and 2h worked well
as reaction partners of 1a (Table 1, entries 9 and 10), while
the reaction of 1c with 2g did not proceed. A substituted
4H-chromene derivative could be obtained in 82% yield by the
reaction of 1b with salicylaldehyde (Scheme 1).
2 (a) T. Okuhara, N. Mizuno and M. Misono, Adv. Catal., 1996,
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A. M. Khenkin, Chem. Commun., 2006, 2529; (e) N. Mizuno,
K. Kamata, S. Uchida and K. Yamaguchi, in Modern Hetero-
geneous Oxidation Catalysis, ed. N. Mizuno, Wiley-VCH,
Weinheim, 2009, pp. 185–216.
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2007, 692, 455; (b) T. Kimura, K. Kamata and N. Mizuno, Angew.
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POM I also efficiently catalyzed cyanosilylation of carbonyl
compounds with trimethylsilyl cyanide (TMSCN) (Scheme 2).
The reaction of an aliphatic aldehyde efficiently proceeded to
give the corresponding cyanohydrin trimethylsilyl ether in
95% yield even with 0.01 mol% of I. In this case, the TOF
was 572 000 h–1, and the turnover number (TON) reached up
to 9530. The reaction of unreactive acetophenone also quanti-
tatively proceeded. The catalytic activity of I was much higher
than that of [(g-SiYW10O36)2]10–, which is reported to be active
for cyanosilylation of carbonyl compounds.8
M. J. Climent, A. Corma, S. Iborra, R. Monton and
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M. J. Sabater, Chem.–Eur. J., 2010, 16, 1221; (h) K. Motokura,
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M. D. Hernadez-Alonso, G. P. M. van Klink and F. Kapteijn,
J. Catal., 2009, 261, 75.
In conclusion, POM I could be synthesized by controlling
the negative charge in an organic medium. POM I could act as
an efficient homogeneous catalyst for Knoevenagel conden-
sation and cyanosilylation, and various combinations of sub-
strates were efficiently converted to the desired products in
high yields.
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Soc. Jpn., 1994, 67, 1186.
8 Y. Kikukawa, K. Suzuki, M. Sugawa, T. Hirano, K. Kamata,
K. Yamaguchi and N. Mizuno, Angew. Chem., Int. Ed., 2012,
51, 3686.
This work was supported in part by the Japan Society
for the Promotion of Science (JSPS) through its ‘‘Funding
Program for World-Leading Innovative R&D on Science and
Technology (FIRST Program)’’ and a Grant-in-Aid for Scientific
c
8424 Chem. Commun., 2012, 48, 8422–8424
This journal is The Royal Society of Chemistry 2012