5320
L.-W. Xu et al. / Tetrahedron Letters 46 (2005) 5317–5320
2. Selected new literature: (a) Sammelson, D. E.; Kurth, M.
+
N
Base
J. Chem. Rev. 2001, 101, 13; (b) Huddleston, R. R.;
Krische, M. J. Synlett 2003, 12; (c) Gibson, S. E.;
Stevenazzi, A. Angew. Chem., Int. Ed. 2003, 42, 1800; (d)
Moreno-Mon˜as, M.; Pleixats, R. Acc. Chem. Res. 2003,
36, 638.
PhCHO
_
N
_
Br-
N
N
+
N
Br-
O
+
N
Ph
Br-
A
B
C
3. (a) Lapworth, A. J. J. Chem. Soc. 1903, 83, 995; (b) Ide,
W. S.; Buck, J. S. Org. React. 1948, 4, 269; (c) Kool, E. T.;
Breslow, R. J. Am. Chem. Soc. 1988, 110, 1196; (d)
Potnick, J. R.; Johnson, J. S. J. Am. Chem. Soc. 2004, 126,
3070.
4. (a) Breslow, R.; Kim, R. Tetrahedron Lett. 1994, 35, 699;
(b) Bausch, C. C.; Johnson, J. S. J. Org. Chem. 2004, 69,
4283.
+
+
N
N
PhCHO
_
Br-
Br-
N
N
HO
O
_
HO
Ph
Ph
Ph
D
E
O
OH
Ph
N
5. (a) Davis, J. H.; Forrester, K. J., Jr. Tetrahedron Lett.
1999, 40, 1621; (b) Murry, J. A.; Frantz, D. E.; Soheili, A.;
Tillyer, R.; Grabowiski, E. J. J.; Reider, P. J. J. Am. Chem.
Soc. 2001, 123, 9696; (c) Tachibana, P.; Kihara, N.;
Takata, T. J. Am. Chem. Soc. 2004, 126, 3438.
6. (a) Welton, T. Chem. Rev. 1999, 99, 2071; (b) Zhao, D.;
Wu, M.; Kou, Y.; Min, E. Catal. Today 2002, 74, 157; (c)
Cosson, A.; Johansson, M.; Ba¨ckvall, J. E. Chem. Com-
mun. 2004, 1494.
+
N
Ph
Br-
F
A
Scheme 3. Mechanism of simple imidazolium salt (EMIMBr) cata-
lyzed benzoin condensation reaction.
7. (a) Tran, K. L.; Weaver, K. J.; Forbes, D. C.; Davis, J. H.
J. Am. Chem. Soc. 2002, 124, 5962; (b) Yadav, J. S.;
Reddt, B. V. S.; Baishya, G. J. Org. Chem. 2003, 68, 7098;
(c) Chauhan, S. M. S.; Kumar, A.; Srinivas, K. A.; Cole,
A. C.; Jensen, J. L.; Nitai, I. Chem. Commun. 2003, 2348;
(d) Xu, L. W.; Li, L.; Xia, C. G.; Zhou, S. L.; Li, J. W.
Tetrahedron Lett. 2004, 45, 1219.
reaction conditions opens a novel green entry to synthe-
sis of a-hydroxyl ketone by simple procedure. Finally,
the successful application of very cheap catalysts bodes
well for the development of asymmetric benzoin reac-
tion. Current efforts are focused on the synthesis of
chiral imidazolium-based catalyst and its application
in this benzoin condensation reaction.
8. Aggarwal, V. K.; Emme, I.; Mereu, A. Chem. Commun.
2002, 1612.
9. Teles, J. H.; Melder, J. P.; Ebel, K.; Schneider, R.; Gehrer,
E.; Harder, W.; Brode, S.; Enders, D.; Breuer, K.; Raabe,
G. Helv. Chim. Acta 1996, 79, 61.
Acknowledgements
10. Xu, L.; Chen, W.; Xiao, J. Organometallics 2000, 19, 1123.
11. Stetter, H.; Kuhlmann, H. Org. React. 1991, 40, 407.
12. General procedure: EMIMBr (191 mg, 1 mmol), aldehyde
(2 mmol), K2CO3 (152 mg, 1.1 mmol), 3 mL of CH2Cl2
and a magnetic stir bar were combined. This mixture was
stirred at room temperature. After the completion, this
mixture was diluted with CH2Cl2 and washed with water.
The organic layer was dried over anhydrous Na2SO4 and
the yield was determined by GC analysis. The organic
layer was filtered, concentrated in vacuo and purified by
flash chromatography on silica gel. All products are
identified by GC/MS and their 1H NMR were identical to
authentic samples.
This study was supported in part by the Natural Science
Founder of National for financial support of the work
(20402017). X.L.W. and L.L. are greatly indebted to
Professor Hu Xin-Gen, School of Chemistry and Mate-
rials Sciences, Wenzhou University, for his helpful
discussion.
References and notes
1. Comprehensive Organic Synthesis; (a) Trost, B. M., Flem-
ing, I., Eds.; Pergmon: New York, 1991; Vols. 1–9; (b)
Basavaiah, D.; Rao, A. J.; Satyanarayana, T. Chem. Rev.
2003, 103, 811.
13. The GC yields in Tables 1 and 2 ignored the consuming
amount of aldehyde which reacted with ionic liquid to
yield trace carbene intermediate.