Typical procedure for the benzoin reaction catalyzed by
methylene-bridged bis(benzimidazolium) salt 1
Ed. Engl., 1997, 36, 2162; (c) A. J. Arduengo, III, Acc. Chem. Res., 1999,
3
2, 913; (d) D. Bourissou, O. Guerret, F. P. Gabba ¨ı and G. Bertrand,
Chem. Rev., 2000, 100, 39; (e) W. A. Herrmann, Angew. Chem., 2002,
14, 1342.
1
Benzaldehyde (2.12 g, 20.0 mmol) was added to water (20 mL). To
the mixture was added methylene-bridged bis(benzimidazolium)
salt 1 and an appropriate base was added. The reaction mixture
was stirred vigorously at room temperature. The benzoin was
filtered, washed with water and dried in the open air. In the case
of unsatisfactory purity, purification by column chromatography
2
(a) J. S. Johnson, Angew. Chem., Int. Ed., 2004, 43, 1326; (b) D. Enders
and T. Balensiefer, Acc. Chem. Res., 2004, 37, 534.
3 J. S. Stetter, Angew. Chem., Int. Ed., 2004, 43, 1326.
4
G. A. Grasa, R. A. Kissling and S. P. Nolan, Org. Lett., 2002, 4,
583.
Y. Suzuki, A. Bakar, K. Muramatsu and M. Sato, Tetrahedron, 2006,
2, 4227.
3
5
6
(
SiO
2
, hexane–AcOEt = 5 : 1) was employed.
6 (a) S. S. Sohn, E. L. Rosen and J. W. Bode, J. Am. Chem. Soc., 2004,
1
2
26, 14370; (b) C. Burstein and F. Glorius, Angew. Chem., Int. Ed.,
004, 43, 6205.
Typical procedure for the self-condensation of aromatic aldehyde
7
T. L. Amyes, S. T. Diver, J. P. Richard, R. F. Rivas and K. Toth, J. Am.
Chem. Soc., 2004, 126, 4366.
(
4) catalyzed by 1,12-bis((1-methylbenz-imidazolium)-3-yl)-
dodecane dibromide (1a)
8 (a) C.-J. Li and T.-H. Chan, Organic Reactions in Aqueous Media, John
Wiley and Sons, New York, 1997; (b) A. Grieco, Organic Synthesis
in Water, Thomson Sciences, London, 1998; (c) C.-J. Li, Chem. Rev.,
Aromatic aldehyde 4 (10.0 mmol) was added to water (10 mL).
To the mixture was added 1a (10 mol%) and DBU (20 mol%)
was added. The reaction mixture was stirred vigorously at room
temperature. The benzoin 5 was filtered, washed with water
and dried in the open air. In the case of unsatisfactory purity,
2
005, 105, 3095.
9
(a) R. Breslow, Acc. Chem. Res., 1991, 24, 159; (b) W. Blokzijl and
J. B. F. N. Engberts, Angew. Chem., Int. Ed. Engl., 1993, 32, 1545; (c) B.
Widom, P. Bhimalapuram and K. Koga, Phys. Chem. Chem. Phys.,
2
003, 5, 3085; (d) O. Sijbren and J. B. F. N. Engberts, Org. Biomol.
Chem., 2003, 1, 2809; (e) U. M. Lindstr o¨ m and F. Anderson, Angew.
Chem., Int. Ed., 2006, 45, 548.
purification by column chromatography (SiO
: 1) was employed.
The structures of the benzoins 5a, 5c were confirmed by
comparison of their spectral data with those reported in the
2
, hexane–AcOEt =
5
1
1
1
0 K. Iwamoto, M. Hamaya, N. Hashimoto, H. Kimura, Y. Suzuki and
M. Sato, Tetrahedron Lett., 2006, 47, 7175.
1 V. P. W. Bohm and W. A. Herrmann, Angew. Chem., Int. Ed., 2000, 39,
4
036.
13
literature. The structures of the benzoins 5b, 5d–h were confirmed
2 (a) I. Bitter, Z. T o¨ r o¨ k, V. Csokai, A. Gr u¨ n, B. Bal a´ zs, G. T o´ th, G. M.
Keser u¨ , Z. Kov a´ ri and M. Czugler, Eur. J. Org. Chem., 2001, 66, 2861;
(b) J. A. Murphy, T. A. Khan, D. W. Zhou, D. W. Thomson and M.
Mahesh, Angew. Chem., Int. Ed., 2005, 44, 1356; (c) V. P. W. Bohm and
W. A. Herrmann, Angew. Chem., Int. Ed., 2000, 39, 4036.
by spectral data, and by comparison of the melting points with
those of authentic samples reported in the literature.
14
References
13 A. Miyashita, Y. Suzuki, K. Iwamoto and T. Higashino, Chem. Pharm.
Bull., 1994, 42, 2633.
14 (a) W. S. Ide and J. S. Buck, Org. React., 1948, 4, 269; (b) M. Gomberg
and F. J. Van Natta, J. Am. Chem. Soc., 1929, 51, 2238.
1
(a) N-Heterocyclic carbene (NHC) reviews:M. Regitz, Angew. Chem.,
996, 108, 791; (b) W. A. Herrmann and C. Kocher, Angew. Chem., Int.
1
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