An inventive approach to the development of chiral Brønsted acid catalysts which possess strong acid functionalities has been accomplished. Because of their unique structural and chemical features, phosphoric acids have become the focus of our attention as potential chiral Brønsted acid catalysts, among the various organic Brønsted acids surveyed. An acidic functionality is available even with the introduction of a ring system which effectively restricts the conformational flexibility of the chiral backbone. In addition, substituents can be introduced to the ring system to provide an efficient chiral environment for enantioselective transformations. Furthermore the phosphoryl oxygen would function as a Brønsted basic site and hence it is anticipated that it would convey acid/base dual function even to monofunctional phosphoric acid catalysts. It can be considered that an efficient substrate recognition site would be constructed around the activation site due to the steric and electronic influence of the substituents introduced at the ring system as well as the acid/base dual function. In this context, we developed 1,1’-bi-2-naphthol (BINOL)-derived monophosphoric acids as chiral Brønsted acid catalysts. The chiral phosphoric acids thus developed functioned as efficient enantioselective catalysts for a variety of carbon-carbon bond forming reactions via activation of a series of functionalities, affording products in an enantioselective manner. In this account article, we review our recent achievements in developing enantioselective reactions using the chiral phosphoric acid catalysts.
2013 社団法人 有機合成化学協会