Chemistry Reference
In-Depth Information
Typical procedure. (
)-(R)-(Cyclopent-2-enyl)methyl chloroformate 50 [34]:
To a mag-
netically stirred solution of diphosgene (2.42 mL, 20 mmol) in dichloromethane
(18 mL), dry pyridine (0.82 mL, 10 mmol) was added at 0
C, and the resulting
suspension was stirred at room temperature for 30 min. Thereafter, a solution of
(
þ
)-(R)-(cyclopent-2-enyl)methanol (980 mg, 10 mmol) in dichloromethane (8 mL)
was added dropwise at 0
C, and the mixture was stirred at room temperature for
5 h. It was diluted with diethyl ether, resulting in a dark-brown liquid (
þ
þ
)-(R)-
(cyclopent-2-enyl)methyl chloroformate (1.30 g, 81%).
Triphosgene [35] or diphosgene [36] have been employed for the preparation of
silicon-containing (52) [37], sulfur (54), and 3,6-disubstituted 2-hydroxy (or thio)
pyrazine (56) chloroformates [38].
CCl
3
OCOCl
Si
Si
Si
OH
Si
O
Cl
PhH, Py, 0°C,2h
O
45 %
51
52
O
O
Cl
OH
O
S
O
O
S
O
CCl
3
OCOCl
MeCN, 5h
N
N
91 %
53
54
N
R
N
R
N
R
1) NaH
t
-BuOH
O
Bu
t
2) 0.5 equiv
Pyridine
R
NX
O
R
N H
R
N
l
CCl
3
OCOCl
55
56
57
X
R Yield %
O Et 43
O i-Pr 53
O i-Bu
50
S
t
5
S
n-Pr 84
S
n-Bu
78
Typical procedure. t-Butoxycarbonylated pyrazinols 57 [38]:
To a solution of a pyra-
zinol (10 mmol) or pyrazinethiol (10 mmol) in dioxane (50 mL), sodium hydride
(480 mg, 10 mg atom) was added and the reaction mixture was stirred at room
