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was employed in acid-catalyzed reactions, which could be conducted in strongly
basic solutions [
21
]. The catalysis of the hydrolysis of orthoformates and acetals
was enhanced by 1,000-fold in basic solution using this principle (Fig.
18
).
Complementary to this strategy, the inner space of these supramolecular
assemblies has been employed to enforce the reactive conformations of substrates.
Unlike the previous example, instead of promoting an otherwise unstable chemical
intermediate, the spatial restrictions of the supramolecular coordination cage pro-
mote the formation of reactive intermediates, as in the aza-Cope electrocyclization
in Fig.
19
. Furthermore, the enantipure form of the assembly could be used to make
OH
O
H
+
H
+
+
+
OH
2
+
Fig. 20 The Nazarov cyclization as catalyzed by the M
4
L
6
assembly
