Chemistry Letters Vol.35, No.9 (2006)
1005
found to decrease the yields of esters (20–30% only). In conclu-
sion, an efficient and simple method for the synthesis of ꢀ-amino
esters from highly constrained ꢀ-lactams has been described us-
ing silica chloride as a heterogeneous catalyst. The main advant-
age of this method is that it requires mild reaction conditions,
less reaction time and operational simplicity with excellent
yields.
by flash chromatography on a silica-gel column (toluene:
ethanol 9:1) to afford ꢀ-aminoester in excellent yield.
10 Analytical data for selected compounds have been reported
here. 1b: Viscous oil, IR ꢁmax 3344, 3223, 1730, 1260
cmꢃ1 1H NMR (CDCl3, 400 MHz) ꢂ 1.27–1.35 (m, 2H),
;
1.70–1.86 (m, 4H), 1.88–2.0 (m, 2H), 2.65 (dd, 1H, J ¼
4:1, 6.4 Hz), 3.16 (m, 1H), 3.67 (s, 3H); 13C NMR (CDCl3,
100 MHz) ꢂ 18.5, 20.3, 31.5, 47.2, 47.6, 50.8, 176. ESI-
MS 144 (M þ H); HRMS calcd for C7H13NO2 143.0946,
found 143.0941. 3b: Viscous oil, IR ꢁmax 3324, 3323,
References and Notes
1
2
1
E. Juaristi, Enantioselective Synthesis of ꢀ-Amino Acids,
New York, 1997.
S. Knapp, Chem. Rev. 1995, 95, 185.
J. S. Park, H. S. Lee, J. R. Lai, B. M. Kim, S. H. Gellman,
1737, 1260 cmꢃ1; H NMR (CDCl3, 400 MHz) ꢂ 1.30–1.85
(m, 8H), 1.89–2.2 (m, 2H), 2.17 (dd, 1H, J ¼ 4:66,
6.04 Hz), 3.17 (m, 1H), 3.68 (s, 3H); 13C NMR (CDCl3,
100 MHz) ꢂ 21.8, 22.2, 24.3, 33.1, 45.1, 45.5, 50.7, 176;
ESI-MS 158 (M þ H); HRMS calcd for C8H15NO2
157.1103, found 157.1100. 5b: Viscous oil, IR ꢁmax 3327,
3
4
5
a) Z. Szakonyi, F. Fulop, G. Bernath, F. Evanics, F. G.
3353, 1747, 1260 cmꢃ1 1H NMR (CDCl3, 400 MHz) ꢂ
:
1.26–1.29 (m, 8H), 1.50–1.64 (m, 4H), 1.88–2.0 (m, 2H),
2.18 (dd, 1H, J ¼ 4:1, 6.6 Hz), 3.25 (m, 1H), 3.68 (s, 3H);
13C NMR (CDCl3, 100 MHz) ꢂ 24.7, 28.3, 29.9, 30.12,
30.2, 36.2, 43.42, 48.54, 50.7, 176; ESI-MS 186 (M þ H);
HRMS calcd for C10H19NO2 185.1416, found 185.1410.
6
7
6b: Viscous oil, IR ꢁmax 3234, 3326, 1736, 1260 cmꢃ1
;
1H NMR (CDCl3, 400 MHz) ꢂ 1.24–1.28 (m, 8H), 1.41–
1.56 (m, 4H), 2.18 (dd, 1H, J ¼ 4:5, 6.8 Hz), 3.17 (m, 1H),
3.67 (s, 3H), 4.06 (d, J ¼ 15:4 Hz, 1H), 4.42 (d, J ¼
15:4 Hz, 1H), 6.17 (brs, 1H, NH), 7.23–7.28 (m, 5H);
13C NMR (CDCl3, 100 MHz) ꢂ 25.2, 25.7, 27.2, 30.1, 30.6,
33.8, 46.5, 51.4, 52.3, 52.8, 127.6, 128.1, 128.7, 130.3,
131.1, 137.2, 176; ESI-MS 276 (M þ H); HRMS calcd for
C17H25NO2 275.1885 found 275.1881.
a) D. M. Tal, E. Keinan, Y. Mazur, Tetrahedron 1998, 37,
4327. b) M. A. Zolfigol, Tetrahedron Lett. 2001, 57, 9509.
a) F. Mohanazadeh, A. R. Momeni, Y. Ranjbar, Tetrahedron
Typical Experimental procedure for the synthesis of ꢀ-amino
esters. To a mixture of ꢀ-lactam (1 mmol) and silica chloride
(1 mmol), dry alcohol (4 mmol) was added drop wise at 0 ꢁC.
The reaction mixture was stirred for 10–20 min. The progress
of reaction was monitored by TLC (toluene:ethanol 9:1). Af-
ter the disappearance of starting material in TLC the reaction
mixture was further basified with cold saturated sodium
bicarbonate solution followed by the extraction with diethyl
ether (3 ꢂ 50 mL). The combined organic layer was dried
(Na2SO4), filtered and evaporated. The oily residue obtained
8
9
11 P. J. Parsons, N. P. Camp, J. M. Underwood, M. D. Harvey,
12 Typical procedure for the preparation of silica chloride. To a
well-stirred silica gel (20 g) in CH2Cl2 (50 mL) was added
drop wise SOCl2 (20 g) at room temperature. Evolution of
copious amounts of HCl and SO2 occurred instantaneously.
After stirring for another 1 h, the solvent was removed to
dryness under reduced pressure (1 torr) to get the silica
chloride (SiO2–Cl).