Chemistry Reference
In-Depth Information
Tab. 4.14.
Aryl isocyanates 338 prepared with Boc
2
O [221].
R
1
R
2
R
3
R
4
R
5
338
Method
a
Yield of
338 (%)
a
Me
H
Me
H
Me
A (B)
96 (93)
b
Me
H
H
H
Me
A
94
c
iPr
H
H
H
iPr
A
99
d
OMe
H
OMe
H
OMe
A
97
e
Me
H
H
H
H
A
44
f
OMe
H
H
H
H
A
86
g
OMe
H
Me
H
H
A
88
h
Me
H
OMe
H
H
A
58
i
OMe
H
OMe
H
H
A
76
j
Me
Me
OMe
H
H
A
89
k
-(CH
b
CH)
2
-
OMe
H
H
A
42
l
H
H
OMe
H
H
B
41
a
Method A: work-up with sulfuric acid (reaction in CH
3
CN at 25
C, 10
min; work-up by addition of H
2
SO
4
(7.0 equiv) in CH
3
CN [40%] and
subsequent extraction with hexane).
Method B: low-temperature chromatographic work-up (reaction in
CH
2
Cl
2
at 25
C, 10 min; purification by column chromatography on
silica gel at
45
Cto
30
C).
amines can be attributed to reaction of the isocyanates with the simultaneously
formed tert-butanol affording an N-Boc derivative (urethane) and to product loss
during work-up.
When the arenediamines 2,4,6-trimethylbenzene-1,3-diamine and 2,2
0
,6,6
0
-
tetramethyl-4,4
0
-methylenediphenylamine were treated under the same reaction
conditions with 1.4 equivalents of Boc
2
O and 1.0 equivalent of DMAP per amino
group in acetonitrile at room temperature (Method A, work-up with sulfuric
acid), 2,4,6-trimethylbenzene-1,3-diisocyanate 339 and 2,2
0
,6,6
0
-tetramethyl-4,4
0
-meth-
ylenediphenyl isocyanate 340 were obtained in yields of 84% and 93%, respectively.
Arenediyl diisocyanates play a very important role as monomers for the industrial
synthesis of polyurethanes and polyureas [226].
NCO
Me
Me
Me
Me
OCN
CH
2
NCO
NCO
Me
Me
Me
339
340
The high e
ciency of 4-dimethylaminopyridine (DMAP) as a catalyst in acylation
reactions has long been recognized. The reactive intermediates of these acylation
reactions are N-acylpyridinium ions [225].
