Chemistry Reference
In-Depth Information
b-cyanoethyl chlorocarbonate was dissolved in anhydrous diethyl ether (50 mL),
placed in a dropping funnel, and added dropwise to a solution of ethanedithiol
(28 mL, 334 mmol) in anhydrous diethyl ether (200 mL) and pyridine (25 mL). The
reaction mixture was filtered, and the filtrate was washed with saturated sodium
hydrogen carbonate solution (3
100 mL) and brine (100 mL) and dried over
Na
2
SO
4
. The organic phase was concentrated to an oil and distilled. The product
was collected at 140-150
C/0.4 mmHg.
Azidobenzyl chloroformate 42, prepared in good yield by reacting 4-azidobenzyl
alcohol 41 with triphosgene in the presence of triethylamine, gave a meagre yield
of a product identical (TLC,
1
H NMR) to 4-azidobenzyl-N-(2-phenylethyl)carbamate
43 on treatment with 2-phenylethylamine [32]. Unfortunately, azidobenzyl chlo-
roformate was isolated as an unstable oil, which proved impossible to purify
further.
O
(CCl
3
O)
2
CO
OH
O
Cl
N
3
Et
3
N,THF 0°C
N
3
41
42
O
NH
2
Ph
Ph
O
H
Et
3
N,THF,12h
N
3
43
Typical procedure. 4-Azidobenzyl-N-(2-phenylethyl)carbamate 43 [32]: To a stirred so-
lution of triphosgene (1.0 g, 3.4 mmol) and 4-azidobenzyl alcohol (1.0 g, 6.7 mmol)
in THF (40 mL), a solution of triethylamine (2.0 g, 19.7 mmol) in THF (40 mL)
was added dropwise over a period of 1 h. The mixture was stirred under nitrogen
in the dark for 72 h at 25
C and, after removal of the solvent, the residue was
partially redissolved in ethyl acetate (25 mL) and filtered through kieselguhr. The
filtrate was washed with water (2
25 mL), dried (MgSO
4
), and the solvent was
evaporated under reduced pressure to give the chloroformate 42 as a photosensitive
viscous yellow oil (0.83 g, 58%), which was used without further purification.
Treatment of a stirred solution of the above chloroformate (0.83 g, 3.9 mmol) in
THF (20 mL), containing triethylamine (0.4 g, 4.8 mmol), with 2-phenylethylamine
(0.54 g, 4.4 mmol) afforded, after 12 h, a product (0.1 g) identical to 4-azidobenzyl-
N-(2-phenylethyl)carbamate.
Acyl azide 46, a starting material for oxazolidine derivatives 47 and 48 of digitalis
steroidal compounds, was prepared by isolating the chloroformate intermediate 45
[33].
