Y. Shimakawa et al. / Tetrahedron Letters 51 (2010) 1786–1789
1789
additional amount of DBU in AcOEt was added, and the reaction
mixture was stirred at 70 °C for 6 h under air atmosphere. The de-
sired a-diketones were obtained in moderate to good yields in all
cases, and the product yields were slightly improved when 4 was
2. Selected recent publications: (a) Uyanik, M.; Akakura, M.; Ishihara, K. J. Am.
Chem. Soc. 2009, 131, 251–262; (b) Heirtzler, F.; Neuburger, M.; Kulike, K. J.
Chem. Soc., Perkin Trans. 1 2002, 809–820; (c) Chang, H. S.; Woo, J. C.; Lee, K. M.;
Ko, Y. K.; Moon, S.-S.; Kim, D.-W. Synth. Commun. 2002, 32, 31–35.
3. Selected recent publications: (a) Ren, W.; Xia, Y.; Ji, S.-J.; Zhang, Y.; Wan, X.;
Zhao, J. Org. Lett. 2009, 11, 1841–1844; (b) Niu, M.; Fu, H.; Jiang, Y.; Zhao, Y.
Synthesis 2008, 2879–2882; (c) Wan, Z.; Jones, C. D.; Mitchell, D.; Pu, J. Y.;
Zhang, T. Y. J. Org. Chem. 2006, 71, 826–828.
used as the catalyst in place of 1 (Runs 1–8). Conversion of 12a to
1
2c was achieved by treating the reaction mixture with methanol
at room temperature under air after the dimerization (Run 9). How-
ever, it was difficult to obtain aliphatic 1,2-diketones from 13a.
4. Katritzky, A. R.; Zhang, D.; Kirichenko, K. J. Org. Chem. 2005, 70, 3271–3274. and
references cited therein.
5.
Selected reviews: (a) Díez-González, S.; Marion, N.; Nolan, S. P. Chem. Rev. 2009,
09, 3612–3676; (b) Hahn, F. E.; Jahnke, M. C. Angew. Chem., Int. Ed. 2008, 47,
1
4
. Conclusions
3122–3172; (c)Topics in Organometallic Chemistry; Glorius, F., Ed.; Springer:
Berlin, 2007; Vol. 21, (d) Douthwaite, R. E. Coord. Chem. Rev. 2007, 251, 702–
7
17; (e) Kantchev, E. A. B.; O’Brien, C. J.; Organ, M. G. Angew. Chem., Int. Ed.
A one-pot synthetic method for synthesizing a-diketones from
aldehydes in the presence of a benzimidazolium compound has
2007, 46, 2768–2813; (f) Herrmann, W. A. Angew. Chem., Int. Ed. 2002, 41,
1290–1309.
6
.
Selected reviews: (a) Enders, D.; Niemeier, O.; Henseler, A. Chem. Rev. 2007,
been developed. A variety of -diketones could be obtained by
a
1
1
07, 5606–5655; (b) Clavier, H.; Nolan, S. P. Annu. Rep. Prog. Chem., Scet. B. 2007,
03, 193–222.
reaction of the corresponding aldehydes in the presence of a cata-
lytic amount of 1 (or 4) and DBU and subsequent oxidation under
air atmosphere. This is a convenient method of obtaining 1,2-dike-
tones from aldehydes via the above-mentioned dimerization-oxi-
dation sequence under metal-free conditions.
7. (a) Dvorak, C. A.; Rawal, V. H. Tetrahedron Lett. 1998, 39, 2925–2928; (b) Knight,
R. L.; Leeper, F. J. Tetrahedron Lett. 1997, 38, 3611–3614.
8.
(a) Enders, D.; Kallfass, U. Angew. Chem., Int. Ed. 2002, 41, 1743–1745; (b)
Knight, R. L.; Leeper, F. J. J. Chem. Soc., Perkin Trans. 1 1998, 1891–1893.
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320; (b) Iwamoto, K.; Hamaya, M.; Hashimoto, N.; Kimura, H.; Suzuki, Y.; Sato,
5
M. Tetrahedron Lett. 2006, 47, 7175–7177.
Acknowledgment
1
0. (a) Sakaguchi, S.; Yoo, K. S.; O’Neill, J.; Lee, J. H.; Stewart, T.; Jung, K. W. Angew.
Chem., Int. Ed. 2008, 47, 9326–9329; (b) Lee, J. H.; Yoo, K. S.; Park, C. P.; Olsen, J.
M.; Sakaguchi, S.; Prakash, G. K. S.; Mathew, T.; Jung, K. W. Adv. Synth. Catal.
This work was supported by a Grant-in-Aid for Scientific Re-
search (C) (20550103) from Japan Society for the Promotion of Sci-
ence (JSPS).
2009, 351, 563–568; (c) Sakaguchi, S.; Kawakami, M.; O’Neill, J.; Yoo, K. S.; Jung,
K. W. J. Organomet. Chem. 2010, 695, 195–200; (d) Yoo, K.; O’Neill, J. S.;
Sakaguchi, S.; Giles, R.; Lee, J. H.; Jung, K. W. J. Org. Chem. 2010, 75, 95–101.
1. Okamoto, M.; Yamamoto, Y.; Sakaguchi, S. Chem. Commun. 2009, 7363–7365.
2. Miyashita, A.; Suzuki, Y.; Iwamoto, K.; Higashino, T. Chem. Pharm. Bull. 1994, 42,
1
1
Supplementary data
2633–2635.
1
1
3. Jing, X.; Pan, X.; Li, Z.; Shi, Y.; Yan, C. Synth. Commun. 2009, 39, 492–496.
4. Unfortunately, the enantio excess of the product 2b was low (10% ee). To the
best of our knowledge, however, little paper concerned with asymmetric
benzoin reaction by the use of a chiral imidazolium salt was known: Orlandi,
S.; Caporale, M.; Benaglia, M.; Annunziata, R. Tetrahedron: Asymmetry 2003, 14,
Supplementary data (experimental procedures and spectro-
3
9
827–3830; Struble, J. R.; Kaeobamrung, J.; Bode, J. W. Org. Lett. 2008, 10, 957–
60.
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