Multicatalyst System

This chapter provides an outline description of multicatalyst systems in asymmetric catalysis, including the history, basic concepts, function, and advantages of multicatalyst systems in the development of new asymmetric reactions. In particular, the comparison of multicatalyst systems with monocatalyst systems is discussed in terms of reactivity, stereoselectivity, and atom utilization. The difference between a catalyst and an additive is also deeply discussed. Catalytic asymmetric reactions using additives to enhance reactivity and stereoselectivity are exemplified and sorted by the types of additives involved. To help readers to get basic knowledge about the reactivity and enantiofacial control of a catalytic asymmetric reaction, a general simplified catalytic cycle using a single chiral catalyst is presented and discussed. Finally, for better understanding of the introduction and discussion about the multicatalyst-promoted asymmetric reactions, some typical substrate activation models are summarized, which are classified into (i) the activation of electrophiles and (ii) the activation of nucleophiles.