Chemistry Reference
In-Depth Information
Tab. 4.4.
Chloroformates 89 prepared from aldehydes 88 and triphosgene [51].
R
Isolated
Yield %
R
Isolated
Yield %
OMe
50
64
MeO
OMe
O
82
66
O
93
94
CH
3
(CH
2
)
8
89
85
62
Ferrocene
Carboxaldehyde
78
NC
O
(CCl
3
O)
2
CO
, 0.1 equiv Pyridine
Cl
O
R
H
CCl
4
, -10 to 40 °C
RO
l
88
89
Yields obtained for acrolein and cyclohexane carboxaldehyde (50% and 89%, re-
spectively) are similar to those reported for the phosgene reaction (54% and 87%),
but reaction of triphosgene with benzaldehyde gives a considerably higher yield
than that reported (82% vs. 68%) [49].
Typical procedure. Cyclohexyl a-chloro chloroformate [51]: To a mechanically stirred
solution of cyclohexane carboxaldehyde (4.05 g, 36.1 mmol) and pyridine (300 mg,
3.79 mmol) in CCl
4
(40 mL) under a nitrogen atmosphere at
20
C, solid tri-
phosgene (5.37 g, 18.1 mmol) was added at such a rate that the reaction tempera-
ture remained between
10
C(
@
5 min). The resulting viscous slurry
was allowed to warm to room temperature over 90 min, and then heated to 40
C
for 1 h. The reaction mixture was allowed to cool and stirred overnight at room
temperature. Filtration of the pyridinium salts followed by removal of the solvent
in vacuo gave
20 and
8 g of crude product, which was purified by distillation (bp 90-
91
C at 10 Torr), thereby affording the desired cyclohexyl a-chloro chloroformate
(6.80 g, 89%).
The chloroformate of the tertiary alcohol 1,1,1-trichloro-2-methylpropan-2-ol 90,
2,2,2-trichloro-tert-butyl chloroformate 91 (TCBoc-Cl ), is a reagent that can be used
to introduce the TCBoc protective group, and is stable under acidic and basic con-
@
