New Strategies for the Synthesis of Tetrasubstituted Chiral Centers: Asymmetric Counteranion-Directed Catalysis
One of the primary goals of synthetic organic chemistry is the development of chemical reactions that selectively introduce molecular diversity in a controlled manner. In this regard, the development of novel methods for highly selective and specific syntheses of complex materials is of great importance. In the development of these novel methods, one of the biggest challenges presented to chemists is the construction of tetrasubstituted stereogenic centers. Although modern chemistry offers access to a plethora of tools to tackle the most complex total syntheses, these processes are expensive and time consuming. On the other hand, Nature effortlessly performs these tasks by employing enzymes – complex machines perfected through millions of years of evolution. In this proposal, we aim to emulate Nature through asymmetric catalysis in order to develop selective and specific protocols for the construction of complex materials comprising tetrasubstituted stereogenic centres as active structural subunits.
We plan to base our new strategic bond forming reactions on ion pairing strategy. This principle has already been exploited in the range of elegant selective asymmetric transformations, but can be limited by relatively low levels of activation offered by these materials. In order to achieve activation of such systems, we plan to extend the principle of ion–binding in catalysis by employing asymmetric counteranion–directed catalysis (ACDC). We envisage exploiting π–face selective anion binding through the use of chiral Brønsted acids to enable enantioselective processes. We have recently demonstrated this strategy in the preparation of chiral tetrasubstituted stereogenic centers of N,S-acetals, and in the first organocatalytic enantioselective aza–Friedel–Crafts addition to diaryl–substituted N–acyl imines. This proposal aims to develop transformations for the generation of complex materials with chiral tetrasubstituted centers by employing ACDC strategies, and lead to the development of more efficient catalyst systems that operate through non–covalent interactions. The project offers a rare opportunity to investigate and exploit an entire manifold of unprecedented catalytic asymmetric organic reactions.