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D. Li et al.
LETTER
Me
In summary, we have developed a mild, efficient, and se-
lective organic reductant, 1-acetyl-2,3-dimethylimidazo-
lidine (1c), for the reduction of aromatic, aliphatic and
a,b-unsaturated aldehydes as well as imines in good
yields. Investigations to understand the reducing mecha-
nism and to evaluate the process with a boarder scope of
substrates are in progress in our laboratory.
Me
Me
I
O
O
MeI
Ac2O
85%
N
N
HN
N
N
N Me
69%
Me
Me
Me
N
H
O
NaBH4
97%
N
Me
Me
Scheme 1
Acknowledgment
NaHCO3 (40 mL). After stirring for 0.5 h, the mixture was
extracted with CH2Cl2, and the organic layers were washed
with brine, and dried over anhyd Na2SO4. Evaporation of
CH2Cl2 in vacuo gave 1-acetyl-2-methylimidazoline (5.46 g)
as an oil (yield: 85%). This product was sufficiently pure for
the next step.
1-Acetyl-2-methylimidazoline (5.8 g, 46 mmol) and MeI
(8.6 mL, 138 mmol) were refluxed in Et2O (30 mL) for 10 h.
After cooling to r.t., acetone (15 mL) was added to the
mixture. The mixture was stirred for several hours, and the
solid obtained was collected by vacuum filtration to give 1-
acetyl-2,3-dimethylimidazolinium iodide (8.5 g) as a white
solid (yield: 69%). 1H NMR (300 MHz, CDCl3): d = 2.39 (s,
3 H), 2.79 (s, 3 H), 3.41 (s, 3 H), 4.29 (m, 2 H), 4.46 (m, 2
H). 13C NMR (75 MHz, CDCl3): d = 172.1, 171.2, 55.5, 49.3,
38.5, 28.1, 19.2. IR (KBr): 2941, 1728, 1654, 1446, 1388,
1298, 1174, 1037 cm–1.
1-Acetyl-2,3-dimethylimidazolinium iodide (0.80 g, 3
mmol) was dissolved in MeCN (10 mL) at 0 °C, followed by
the addition of NaBH4 (0.125 g, 3.3 mmol). After the
addition, the reaction mixture was stirred at r.t. for an
additional 5 h. The reaction was quenched with H2O (50
mL). The mixture was extracted with CH2Cl2, and the
organic layers were washed with brine, and dried over anhyd
Na2SO4. Evaporation of CH2Cl2 in vacuo gave 1-acetyl-2,3-
dimethylimidazolidine (1c; 0.42 g) as a clear oil (yield:
97%). 1H NMR (300 MHz, D2O): d = 1.33–1.50 (3 × d, J =
6.3 Hz, 3 H), 2.05–2.11 (3 × s, 3 H), 2.63–2.69 (3 × s, 3 H),
3.27–3.88 (3 × m, 4 H), 4.76–4.90 (m, 1 H). IR (film): 2956,
2381, 1718, 1652, 1419, 1265, 1182 cm–1. MS: m/z = 142
[M+], 127 [M –15], 99 [M – 43]. Anal. Calcd for C7H14N2O:
C, 59.12; H, 9.92; N, 19.70. Found: C, 59.24; H, 9.89; N,
19.75.
We thank the National Natural Science Foundation of China (No.
20502014, 20772073) for financial support.
References and Notes
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J. Am. Chem. Soc. .
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(b) Hasegawa, E.; Seida, T.; hiba, N.; Takahashi, T.; Ikeda,
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The deuterated 1c (C-2 position) was synthesized by the
same procedures except that NaBD4 was used. 1H NMR (300
MHz, D2O): d = 1.22–1.36 (3 × s, 3 H), 1.93–1.99 (3 × s, 3
H), 2.51–2.56 (3 × s, 3 H), 3.15–3.73 (3 × m, 4 H).
(12) Zhang, B.; Zhu, X.-Q.; Lu, J.-Y.; He, J.; Wang, P. G.; Cheng,
J.-P. J. Org. Chem. 2001, 68, 3295.
(13) General Procedure for the Transfer Hydrogenation
Reaction with Imidazolidine 1c as Reductant
Procedure Using Condition A: To a solution of substrate (1
mmol) in MeOH (2 mL) was added a solution of
imidazolidine 1c (0.142 g, 1 mmol) in anhyd MeCN (2 mL).
The reaction mixture was stirred under reflux and monitored
by TLC. Upon completion, the solvent was removed in
vacuo and the residue was chromatographed on silica gel to
give the desired products.
(10) Li, D.; Zhang, Y.; Xia, C.; Guo, W. Heterocycles 2005, 65,
1829.
Procedure Using Condition B: To a solution of substrate (1
mmol) and Mg(ClO4)2 (22.3 mg, 0.1 mmol) in MeOH (2
mL) was added a solution of imidazolidine 1c (0.142 g, 1
mmol) in anhyd MeCN (2 mL). The reaction mixture was
stirred at r.t. and monitored by TLC. Upon completion, the
solvent was removed in vacuo and the residue was
chromatographed on silica gel to give the desired products.
(14) Tanner, D. D.; Chen, J. J. J. Org. Chem. 1989, 54, 3842.
(11) Synthesis of 1-Acetyl-2,3-dimethylimidazolidine (1c)
(Scheme 1):
2-Methylimidazoline (4.3 g, 51 mmol) was dissolved in
CH2Cl2 (15 mL) at 0 °C, followed by the addition of Et3N
(5.2 g, 51 mmol). This solution was then added dropwise to
a solution of Ac2O (5.2 g, 51 mmol) in CH2Cl2 (5 mL). After
the addition, the reaction mixture was stirred at r.t. for an
additional 3 h. The resulting solution was treated with 10%
Synlett 2008, No. 2, 225–228 © Thieme Stuttgart · New York