Chemistry Reference
In-Depth Information
1
CATALYTIC ASYMMETRIC SYNTHESIS
IN NONCONVENTIONAL MEDIA/
CONDITIONS
CHIKAKO OGAWA * AND SH
Ū
KOBAYASHI
Department of Chemistry, School of Science and Graduate School of Pharmaceutical
Sciences, The University of Tokyo, Hongo, Bunkyo - ku, Tokyo 113 - 0033, Japan
1.1. INTRODUCTION
Conventionally, catalytic asymmetric synthesis has been carried out in organic solvents,
because most organic materials are not soluble in other solvents. However, asymmetric
catalysis in other solvents (nonconventional solvents) is now of interest for many reasons.
First and most signifi cantly, the negative characteristics of organic solvents have come to
the fore recently; many organic solvents are volatile, fl ammable, sometimes explosive, and
have a damaging effect on human health (e.g., mutagenic or carcinogenic) or on the envi-
ronment. On the other hand, recovery and reuse of catalysts is crucial in organic synthesis
not only from an economical aspect but also from an environmental point of view. Use of
nonconventional solvents often enables the recovery and reuse of catalysts.
In this chapter, water, fl uorous solvents, supercritical fl uids (SCFs), and ionic liquids
(ILs) are discussed as nonconventional solvents, and characteristic features of asymmetric
catalysis are surveyed. Microwave - assisted catalytic asymmetric synthesis is also described.
1.2. CATALYTIC ASYMMETRIC SYNTHESIS IN WATER
Water is remarkable in nature; indeed, nature chooses water as a “solvent.” Many
elegant
in vitro
reactions, mainly catalyzed by enzymes, are carried out in an aqueous
