738
M. Yasumoto et al. / Journal of Fluorine Chemistry 128 (2007) 736–739
simple work-up after the condensation reaction (only evapora-
tion of the solvent without any further purification) and (2) a
base-free 1,3-proton shift reaction.
Acknowledgements
This work was supported by Department of Chemistry and
Biochemistry, University of Oklahoma. The authors gratefully
acknowledge generous financial support from Central Glass
Company (Tokyo, Japan) and Ajinomoto Company (Tokyo,
Japan).
In conclusion, we found the unprecedented example of a
base-free 1,3-proton shift reaction. This finding allows us to
prepare the amine 1 in high chemical yield and purity via
biomimetic transamination of a,a,a-trifluoroacetophenone 2
with benzylamine under operationally convenient conditions.
The detail mechanistic studies of the thermal 1,3-proton shift
reaction are in progress now.
References
[
1] For the most recent collections of research articles, see:;
3
. Experimental
(
(
(
a) V.A. Soloshonok, V.A. Petrov (Guest Editors), J. Fluor. Chem. 125 (4)
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3
.1. General methods
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Unless otherwise noted, all reagents and solvents were
[2] For the most recent collection of review articles, see:
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obtained from commercial suppliers and used without further
purification. All the reactions were carried out under regular
atmosphere without any special caution to exclude air. Unless
[
3] V.A. Soloshonok, in: P.V. Ramachandran (Ed.), Asymmetric Fluoro-
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1
19
indicated, H, F NMR spectra were taken in CDCl solutions
3
at 299.95 and 282.24 MHz, respectively on an instrument in the
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[
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1
Chemical shifts refer to TMS ( H NMR) and fluorotrichlor-
1
9
omethane ( F NMR) as the internal standards. Yields refer to
isolated yields of products with greater than 95% purity as
6
);
(
b) V.A. Soloshonok, in: I. Ojima, J.R. McCarthy, J.T. Welch (Eds.),
1
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.2. Procedure for preparation of a-
trifluoromethyl)benzylamine (1) from a,a,a-
(
trifluoroacetophenone (2)
7
).
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(
(
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2
8.7 mmol) and acetic acid (1.90 g, 31.6 mmol) in benzene
20 mL), a benzene (9 mL) solution of benzylamine 3 (3.38 g,
1.5 mmol) was added at r.t. The solution was refluxed with
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(
3
(c) V.A. Soloshonok, D.O. Berbasov, in: E.C. Juaristi, V.A. Soloshonok
(
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azeotropic removal of water for 1 day using a Dean-Stark trap.
Then, benzene was removed under reduced pressure. The
mixture was heated at 200 8C for 24 h. Upon the completion of
[
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compounds, see:
1
9
isomerization (monitored by F NMR), the product imine 5
6.20 g) was obtained by distillation (130 8C/5 mmHg). Imine 5
was stirred with 3N HCl (50 mL) and diethyl ether (10 mL) for
day at r.t. After separation, aqueous layer was washed with
(
a) T. Ono, V.P. Kukhar, V.A. Soloshonok, J. Org. Chem. 61 (1996) 6563;
(
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1
diethyl ether (20 mL). Water was removed under reduced
pressure to provide hydrochloride salt of amine 1. The salt was
dissolved with ethyl acetate, 3N NaOH aq. was added until the
aqueous layer became pH 14. After extraction of the aqueous
layer, the ethyl acetate was removed under reduced pressure to
give a-(trifluoromethyl)benzylamine 1 (3.90 g, 78% yield from
Chem. 63 (1998) 1878.
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(
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9] For reviews, see:
4
(
1
19
acetophenone 2) (>95% purity by H, F NMR).
[
[
6
3
.3. N-Benzylidene-1-phenyl-2,2,2-trifluoroethylamine 5
6a]
(
(
a) M.E. Tanner, Acc. Chem. Res. 35 (2002) 237;
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[
[
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1
H NMR d 4.80 (q, 1 H, J = 7.6 Hz), 7.38–7.46 (m, 6 H),
.55–7.57 (m, 2 H), 7.83–7.85 (m, 2 H), 8.39 (s, 1 H); mp
6.5 8C.
7
7
4
(