Chemistry Reference
In-Depth Information
warm to room temperature. The resulting homogeneous solution was quenched
with saturated aq. ammonium chloride solution and the aqueous layer was sepa-
rated and extracted with dichloromethane. The combined organic extracts were
washed with 1 n aq. HCl, saturated aq. NaHCO
3
solution, and brine, dried
(Na
2
SO
4
), filtered, and concentrated in vacuo. Products 906 were purified by flash
column chromatography on silica gel.
3-O-Benzyl-1,2-O-isopropylidene-a-d-glucofuranose-5,6-carbonate 908 has been
synthesized with triphosgene in pyridine at
5
C, whereby the cyclic carbonate
was obtained in 89% yield. This method is amenable to scale-up [656].
þ
HO
O
O
89 %
(Cl
3
CO)
2
CO
O
O
O
O
O
HO
CH
3
CH
3
CH
3
CH
3
BnO
pyridine
5°C
BnO
O
O
907
908
Typical procedure. 3-O-Benzyl-1,2-O-isopropylidene-a-
d
-glucofuranose-5,6-carbonate 908
[656]:
A three-necked, round-bottomed flask was charged with 3-O-benzyl-1,2-O-
isopropylidene-a-d-glucofuranose 907 (35.94 g, 115.84 mmol) and dry pyridine (110
mL). The solution was cooled to an internal temperature of
5
C, and then tri-
phosgene (11.50 g, 38.76 mmol) was added in portions, using an addition funnel
for solids, over a period of 80 min. Stirring was continued for 1 h. The reaction
mixture was then diluted with chloroform (550 mL) and washed with water
(1
þ
150 mL). The organic layer was dried over anhydrous magne-
sium sulfate, filtered, and concentrated in vacuo. The crude material was purified
by azeotropic distillation with toluene (2
220 mL, 1
60 mL) and dried in vacuo overnight.
The product was purified on a flash chromatography column, eluting with EtOAc/
hexanes (25:75
100:0). The appropriate fractions were combined and concen-
trated. The product 908 was isolated in 89% yield.
A polycarbonate has been prepared in 75% yield from bisphenol A and tri-
phosgene [53]; for literature on polycarbonates, see [657, 687].
!
O
(Cl
3
CO)
2
CO
H
O
OH
O
O
n
DCM, Et
3
N
rt, 8 h
909
910
Typical procedure. Bisphenol A polycarbonate 910 [53]: To a solution of 2,2-bis-(4-
hydroxyphenyl)propane 909 (0.68 g, 3 mmol) in dichloromethane (10 mL) was
added triethylamine (0.60 g, 6 mmol), followed by a solution of triphosgene (0.30 g,
