Chemistry Reference
In-Depth Information
2C
ASYMMETRIC PHASE - TRANSFER AND
ION PAIR CATALYSIS
SEIJI SHIRAKAWA AND KEIJI MARUOKA
Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo-ku,
Kyoto 606 - 8502, Japan
2C.1. INTRODUCTION
Phase-transfer catalysis has long been recognized as a versatile methodology for organic
synthesis in both industry and academia, featuring simple experimental operations, mild
reaction conditions, inexpensive and environmentally benign reagents and solvents, and
the possibility of conducting large-scale preparations in process chemistry [1]. In particu-
lar, in the recent past, asymmetric phase-transfer catalysis based on the use of structur-
ally well - defi ned chiral, nonracemic catalysts has become a topic of great scientifi c
interest, and recent efforts have resulted in notable achievements, making it feasible to
perform various bond formation reactions under mild phase-transfer catalyzed condi-
tions [2]. This chapter focuses on the recent aspects of asymmetric transformations using
various types of chiral phase-transfer catalysts. Also, related chiral quaternary ammo-
nium and phosphonium salts as ion pair catalysts are introduced in this chapter.
2C.2. PIONEERING WORK
Although initial work on asymmetric alkylation of carbonyl compounds by chiral phase-
transfer catalyst has yielded disappointing results, a fi rst effi cient chiral phase-transfer
catalyst,
N
- (4 - trifl uoromethylbenzyl)cinchoninium bromide (
1a
), has been devised in
1984 by the Merck group for asymmetric alkylation of 6,7 - dichloro - 5 - methoxy - 2 - phenyl -
1-indanone, giving the corresponding methylation product with 92% ee in this particular
case (Scheme 2C.1 ) [3] .
