Chemistry Reference
In-Depth Information
O
O
N
N
CF
3
O
O
CF
3
O
O
879
80-90 %
880
88 %
Typical procedure. Bis(2,2,2-trifluoroethyl) carbonate 880 [641]:
A solution of 2,2,2-
trifluoroethanol (200 g, 2.0 mol) and pyridine (158 g, 2.0 mol) in dry diethyl ether
(1 L) was treated with phosgene (for a safe source, see Chapter 7) (99 g, 1.0 mol).
The reaction mixture was stirred overnight and then filtered. The filtrate was dis-
tilled to give 199 g (88%) of bis(2,2,2-trifluoroethyl) carbonate 880;bp65-66
C (100
mmHg); IR: n
max
1780 cm
1
O).
Unsymmetrical carbonates 884 [642] can be synthesized in two steps from N-
hydroxy-5-norbornene-2,3-dicarboxamide 881, phosgene, and the appropriate alco-
hols 883. The activated carbonates 884 are excellent reagents for the introduction of
all currently used urethane protecting groups, such as Z, Boc, and Fmoc residues.
¼
(C
b
881
884
882
O
O
O
883
O
O
COCl
2
R-
OH
R
N
O
O
N
OH
N
O
Cl
pyridine
DMA
5°C to rt
4 h
rt to 35°C
4 h
85 %
O
O
O
R-OH =
H
H
H
O
General procedure. Preparation of carbonates 884 [642]:
A solution of 881 (17.9 g, 0.1
mol) and N,N-dimethylaniline (12 g, 0.095 mol) in THF/benzene (1:3, 100 mL) was
added dropwise to a solution of phosgene (for a safe source, see Chapter 7) (9.9 g,
0.1 mol) in benzene (50 mL) at 0-5
C. The mixture was stirred for 1 h at 5
C and
for 3 h at room temperature. The amine hydrochloride was filtered off, and the
filtrate was concentrated to dryness in vacuo. The residue was redissolved in di-
chloromethane (50 mL), and a trace of bis(5-norbornene-2,3-dicarboximido) carbo-
nate was removed by filtration. The solvent was removed in vacuo, and the residue
was triturated with diethyl ether (50 mL) to give 882; yield 20.5 g (85%); mp 98-
100
C (dec.); IR (KBr): n
max
1815, 1795, 1740 cm
1
O).
882 (24.1 g, 0.1 mol) was dissolved in an inert solvent (toluene, benzene, THF, or
a halogenated hydrocarbon; 150 mL) and a solution of the appropriate alcohol 883
(0.1 mol) and pyridine (8 mL) in an inert solvent (40 mL) was added at 10-15
C.
The reaction mixture was stirred for 1 h at room temperature and for 3 h at 35
C.
The pyridinium hydrochloride precipitate was filtered off and the filtrate was con-
centrated to dryness. Further purification was carried out either by recrystallization
of the solid from 90% aqueous methanol or by extraction of the impurities from
a dichloromethane solution first with 5% aqueous sodium hydrogen carbonate so-
¼
(C
b
