2
. Notes
1
.
The checkers purchased N-(tert-butoxycarbonyl)-L-serine
methyl ester from Aldrich Chemical Company, Inc. The submitters
prepared this compound, a thick amber oil, according to the procedure
described in Dondoni, A.; Perrone, D. Org. Synth. Coll. Vol. X, 2004, 320.
2
.
The checkers purified dichloromethane by pressure filtration
through activated alumina.
The checkers purchased 4-DMAP and Me N·HCl from Aldrich
3
.
3
Chemical Company, Inc. Et N was purchased from Alfa Aesar Chemical
3
Company and was distilled from CaH . The submitters obtained 4-DMAP
2
and Et N from Lancaster and Me N·HCl from Aldrich Chemical Company,
3
3
Inc.
4
.
TsCl was obtained from Aldrich Chemical Company, Inc. and
purified by recrystallization according to the following procedure. p-
Toluenesulfonyl chloride (85 g) is dissolved in 150 mL of hot CHCl and
3
200 mL of petroleum ether (room temperature) is added in one portion to the
clear, colorless solution. The resulting cloudy solution is clarified by
addition of ca. 5 g of charcoal, stirred for 1 min, and filtered on a Büchner
funnel. The filtrate is concentrated to ca. 1/5th of its original volume by
rotary evaporation, and the solid which appears is collected by filtration and
dried under reduced pressure (25 °C, 0.03 mm) to afford 68 g of TsCl as
bright white crystals.
5
.
Triethylamine addition must be carried out slowly to avoid
base-promoted elimination of p-toluenesulfonate in the final product.
It may be necessary to scratch the flask in order to start
crystallization.
The product exhibits the following properties: mp 74-76 °C,
6
.
7
.
7
a
20
D
7b
lit. 74-75 °C; [ꢀ] + 3.0 (methanol, c 2.0), lit. +4.6 (methanol, c 2); Rf
-
1
0
1
2
1
.24 (petroleum ether/EtOAc 3:1); IR (CH Cl ) cm : 3384, 2979, 1753,
2
2
1
714, 1511, 1367, 1191, 1177; H NMR (500 MHz, CDCl ) ꢁ: 1.43 (s, 9 H),
3
.46 (s, 3 H), 3.71 (s, 3 H), 4.29 (dd, J = 10.1, 3.1 Hz, 1 H), 4.40 (dd, J =
0.1, 3.1 Hz, 1 H), 4.50-4.53 (m, 1 H), 5.30 (d, J = 7.9 Hz, NH), 7.37 (app d,
1
3
J = 7.9 Hz, 2 H), 7.77 (app d, J = 8.2 Hz, 2 H); C NMR (125 MHz, CDCl )
3
ꢁ
: 21.9, 28.4 (3 C), 53.1 (2 C), 69.7, 80.7, 128.2 (2 C), 130.1 (2 C), 132.5,
80