LETTER
Synthesis of Oxazolines and Imidazolines
1483
Table 4 Reaction of Arylaldehyde and 2-Aminoethanol with PHPB in H2Oa (continued)
N
R
R
HO(CH2)2NH2
PHPB–H2O
CHO
O
c
S
Run
11
Substrate (S)
Molar ratio (S) PHPB Time (h)
Product
Yield (%)
92
N
2.0
19
40
CHO
O
12
12c
N
N
OHC
CHO
12
13
4.0f
91g
83i
O
O
13
13c
N
N
O
3.0h
39
OHC
CHO
O
14
14c
a Reagents and conditions: substrate (S, 0.25 mmol), HO(CH)2NH2 (1.5 mmol), H2O (6 mL), r.t.
b Recovered 5: 16%.
c Hydroxyimine: 25%.
d Recovered 10: 23%.
e Recovered 11: 15%.
f HO(CH2)2NH2: 3.0 mmol.
g Monoaldehydeoxazoline: 2%.
h HO(CH2)2NH2: 2.2 mmol.
i Monoaldehydeoxazoline: 10%.
(3) (a) Bhor, S.; Anilkumar, G.; Tse, M. K.; Klawonn, M.;
Dobler, C.; Bitterlich, B.; Grotevendt, A.; Beller, M. Org.
Lett. 2005, 7, 3393. (b) Langlois, Y.; Dalko, P. I. J. Org.
Chem. 1998, 63, 8107. (c) Jones, R. C. F.; Nichols, J. R.
Tetrahedron Lett. 1990, 31, 1771.
In conclusion, PHPB–H2O in the presence of an ethylene-
diamine system was found to be a simple and chemoselec-
tive method for the transformation of various aromatic
aldehydes into 2-substituted imidazolines without over-
oxidation to carboxylic acid.1e,5b,6,14 Furthermore, the
PHPB–H2O system in the presence of 2-aminoethanol
was also confirmed to be an alternative convenient and
chemoselective procedure for the conversion of aromatic
aldehydes to 2-substituted oxazolines.1c,5,15
(4) (a) Nishiyama, H.; Sakaguchi, H.; Nakamura, T.; Horihata,
M.; Kondo, M.; Ito, K. Organometallics 1989, 8, 846.
(b) Nishiyama, H.; Park, S.-B.; Itoh, K. Tetrahedron:
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Synlett 2006, No. 10, 1479–1484 © Thieme Stuttgart · New York