Chapter 22: Chiral Imidazoles and Pyridines as Asymmetric Organocatalysts

Chiral pyridines and imidazoles have attracted much attention as powerful and useful organocatalysts for asymmetric transformations. In many cases, 4-N,N-dialkylpyridines and N-alkylimidazoles function as catalytically active species for nucleophilic catalysis. Several types of asymmetric reactions including acyl-, phosphoryl-, and sulfonyl transfer reactions as well as Morita–Baylis–Hillman reactions have been developed by nucleophilic catalysis. On the other hand, asymmetric silylation reactions catalysed by an N-alkyl imidazole derivative was proposed to proceed via general base catalysis rather than nucleophilic catalysis. In the first part of this chapter, typical chiral pyridine and imidazole catalysts are described with representative asymmetric transformations. The second part of this chapter focuses on site-selective transformations of multifunctionalised substrates catalysed by chiral pyridines and imidazoles. These site-selective molecular transformations have great potential for green/sustainable chemistry, because these reactions allow the introduction of the requisite functionality directly to the specific site of complex molecules with minimum use of the protective groups.