Journal of the American Chemical Society
ARTICLE
the resulting filtrate was concentrated under reduced pressure. The
crude product was purified by column chromatography (EtOAc:hexane =
1:4) to provide 3l (0.1544 g, 0.476 mmol, 95%) as a clear colorless oil.
Ethyl 2-Benzoyl-5-oxo-5-phenylpentanoate (3l) (Table 6,
entry 9). Rf 0.36 (EtOAc:hexane = 1:4); IR (neat, NaCl): 3064 (m),
2981 (s), 2937 (s), 1974 (w), 1913 (w), 1734 (s), 1686 (s), 1596 (m),
1448 (s), 1221 (s), 974 (s) cm-1; 1H NMR (CDCl3, 500 MHz) δ 8.07
(d, J = 7.9 Hz, 2H), 7.95 (d, J = 7.4 Hz, 2H), 7.59-7.53 (m, 2H),
7.50-7.43 (m, 4H), 4.57 (dd, J = 7.9, 6.2 Hz, 1H), 4.19-4.10 (m, 2H),
3.22-3.16 (m, 1H), 3.12-3.06 (m, 1H), 2.49-2.36 (m, 2H), 1.15 (t, J =
7.4 Hz, 3H); 13C NMR (CDCl3, 125 MHz) δ 199.2, 195.3, 169.8, 136.6,
135.9, 133.6, 133.1, 128.71, 128.70, 128.6, 128.0, 61.4, 52.8, 35.6, 23.2,
13.9; ESI-HRMS (m/z) calcd for C20H20O4 [(M þ H)þ]: 325.14398,
found: 325.14334.
(8) NaBH4 is a common reducing agent used for the formation of
nanoclusters from metal salts. However, to the best of our knowledge,
the possibility of boron remaining and acting as a catalyst has yet been
explored.
(9) Boron-free PI-Au was prepared by the microencapsulation of
pre-prepared PPh3-stabilized Au nanoclusters with the styrene-based
polymer, followed by thermally induced cross-linking. Alternatively,
boron-free PI-Au can be prepared by stirring the boron-containing
immobilized Au catalyst in a THF/H2O solution overnight, followed by
filtration and drying. For the preparation of PPh3-stablized Au nanoclus-
ters, see: Shichibu, Y.; Negishi, Y.; Tsukuda, T.; Teranishi, T. J. Am.
Chem. Soc. 2005, 127, 13464.
(10) We found that mixing hydroquinone with NaB(OMe)4 in
DCM results in an unidentified blue solid.
(11) The Michael reaction between β-ketoester 1a and methyl vinyl
ketone with 3 equiv of K2CO3 in DCM (C = 1.0 M) provided 53% of the
Michael adduct 3a along with undesired side products. From our
previous studies, we have found that PI bimetallic Au-M nanoclusters
can facilitate the oxidation of alcohols under base-free conditions. See:
Miyamura, H.; Matsubara, R.; Kobayashi, S. Chem. Commun. 2008,
2031.
’ ASSOCIATED CONTENT
S
Supporting Information. Detailed experimental proce-
b
dures and characterization of all new compounds. This material is
(12) From our previous studies, relatively low levels of Au nanoclus-
ters could be loaded on the polymer support (0.07-0.08 mmol/g of Au)
to ensure small cluster size and high catalytic activity. We have found that
a polymer-carbon black composite material facilitates high Au loading
(0.25 mmol/g of Au) while maintaining small cluster size and high
catalytic activity. See: Lucchesi, C.; Inasaki, T.; Miyamura, H.; Matsu-
bara, R.; Kobayashi, S. Adv. Synth. Catal. 2008, 350, 1996.
(13) Kaizuka, K.; Miyamura, H.; Kobayashi, S. J. Am. Chem. Soc.
2010, 132, 15096.
(14) (a) Gꢁomez-Bengoa, E.; Cuerva, J. M.; Mateo, C.; Echavarren,
A. M. J. Am. Chem. Soc. 1996, 118, 8553. (b) Campa~na, A. G.; Fuentes,
N.; Gꢁomez-Bengoa, E.; Mateo, C.; Oltra, J. E.; Echavarren, A. M.;
Cuerva, J. M. J. Org. Chem. 2007, 72, 8127.
(15) Abraham, S.; Sundararajan, G. Tetrahedron 2006, 62, 1474.
(16) It is most likely that the tetravalent boron is only the resting
state for the true catalyst for the Michael reaction. NaB(OMe)4 is in
equilibrium with B(OMe)3 and NaOH and may act as a bifunctional
acid-base catalyst. For further discussion of the catalytic activity of
NaB(OMe)4, see ref 14b.
’ AUTHOR INFORMATION
Corresponding Author
’ ACKNOWLEDGMENT
This work was partially supported by a Grant-in-Aid for
Scientific Research from the Japan Society of the Promotion of
Science (JSPS), ERATO (JST), NEDO, and GCOE. W.-J.Y.
thanks JSPS for the JSPS Postdoctoral Fellowship for Foreign
Researchers. We also thank Mr. Noriaki Kuramitsu (The Uni-
versity of Tokyo) for STEM, EDS, and SEM analyses, and Mr.
Tomoyoshi Higashi, Mr. Yoshikuni Okumura, and Mr. Tetsuo
Nakajo (SDK) for N2 adsorption/desorption analysis.
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’ NOTE ADDED AFTER ASAP PUBLICATION
After this paper was published ASAP February 8, 2011, the
description of the preparation of PI/CB-B was modified in the
Experimental Section. The corrected version was published
February 11, 2011.
3103
dx.doi.org/10.1021/ja110142y |J. Am. Chem. Soc. 2011, 133, 3095–3103