Chemistry Reference
In-Depth Information
11
Perspectives
Tsutomu Ishikawa
1
and Davor Margetic
2
1
Graduate School of Pharmaceutical Sciences, Chiba University, 1-33 Yayoi, Inage,
Chiba 263-8522, Japan
2
Rudjer Boskovic Institute, Bijenicka c. 54, 10001 Zagreb, Croatia
Organic bases attract much attention as environment friendly chemicals due to their easy
structural modification, repeated use of recovered materials and simple operation based on
the acid-base concept [1]. The functions of organosuperbase catalysts and of the related
intelligent molecules in organic synthesis (reaction) are attributable to their affinity to form
substrates through their stronger or lesser proton (or nucleophile) affinity. In the cases of a
superbase with strong basicity, salt formation resulting from preliminary reaction with the
substrate is crucial for the desired reaction course, whereas with an intelligent molecule that
is not necessarily strongly basic but is able to form tight hydrogen bonding with the
substrate, control of the reaction is by interaction through hydrogen bond network(s). In
particular, for effective asymmetric induction it is very important for the active site in the
catalyst to selectively (or specifically) recognize target groups in the substrate and then to
construct a rigid, but flexible, chiral environment in transition state. Therefore, complexa-
tion not only through mono-interaction between each functional group in the catalyst and in
the substrate, but also through multi-interaction containing additional functional group(s)
in some cases is required for effective molecular recognition. Thus, a lot of intelligent
molecules with multi-functions have been designed and prepared by introducing different
functional, but mutually noninteractive, groups to the original molecule [2].
Individual reaction in living organisms is strictly controlled by reactant-substrate
specificity, as exemplified in enzymatic reactions, even though the total mode of action
is systematically controlled by correlation with other reactions. Host-guest interaction in
inclusion chemistry using cyclodextrin [3] is a typical example of specific reactions in an
artificial field. On the other hand, nonspecific catalysts that are tolerant to various functional
