Читать книгу Catalytic Asymmetric Synthesis - Группа авторов - Страница 87

Asymmetric organocatalysis has become a powerful strategy for the construction of chiral functional molecules and materials, providing unique reactivity manifolds compared to traditional metal‐catalyzed or enzymatic‐based approaches. Within the field, reversible covalent substrate activation or binding with a chiral catalyst (enamine, iminium, or N‐heterocyclic carbene [NHC] catalysis) has been extensively exploited to achieve highly enantioselective transformations. Conformational analysis of the catalyst‐bound intermediates has permitted the rationalization of the origin of enantioselectivity in a number of reactions, which in turn has helped drive catalyst design with relative ease. Another approach involves the use of noncovalent interactions as the basis for substrate activation and asymmetric induction. Within this category, asymmetric phase‐transfer and ion‐pairing catalyses have proven to be uniquely suited to achieve highly selective reactions involving charged substrates or intermediates (Scheme 4.1). This chapter will cover key historical and recent developments in the area of chiral cation phase‐transfer and cation‐binding catalyses, in addition to more recent advances in chiral‐anion (phase‐transfer) and anion‐binding catalyses. Additionally, examples featuring transition‐metal and phase‐transfer dual catalysis will also be highlighted.