Chemistry Reference
In-Depth Information
O
O
Basic Al
2
O
3
(3.5 g)
Ball-milling (600 rpm)
rt, 2-3 h, 66-81%
R
2
R
3
R
2
R
3
+
OH
+
OH
R
1
R
1
O
O
Some selected examples
:
O
O
O
O
O
O
OCH
3
NO
2
Cl
71%
81%
81%
O
O
O
N
O
O
O
S
O
71%
66%
65%
O
O
O
O
O
O
74%
66%
68%
Scheme 1.20 Transesterification under ball milling.
MX
M = Na, K, Cs
X = F, Cl, I, SCN, N
3
Ball-milling (50 Hz), 1h
14-97%
KX, 18-crown-6
X = F, Cl, I, CN, OAc
Ball-milling (50 Hz), 1h
70-90%
X
Br
Br
Br
X
Br
Scheme 1.21 Reaction between 4-bromobenzyl bromide and alkali salts with or
without 18-crown-6 by ball milling.
methanols participated in the transesterification reaction without any
diculty.
1.2.3 C-X (X
¼
F, Cl, I, SCN, OAc etc.) Bond Forming
Reaction
Mack et al. have reported the heterogeneous nucleophilic additions of alkali
salts of thiocyanate, azide, acetate and halides to 4-bromobenzyl bromide
with or without 18-crown-6 by ball milling (Scheme 1.21).
24
It was found that
thiocyanate and azide provided excellent yields of the nucleophilic addition
products, whereas the potassium and sodium salts of fluoride, chloride,
acetate and cyanide provided relatively low yields of the corresponding
addition products. On the other hand, 18-crown-6 can complex with K
1
cation to increase the basicity and nucleophilicity of the employed nucleo-
philes, and thus the addition of 18-crown-6 led to a better conversion and
increase in yield for all of the potassium salt nucleophiles including fluoride,
acetate and cyanide,
25
which were previously unsuccessful.
24
Search WWH ::
Custom Search