Developing Catalytic Asymmetric Acetalizations

Acetals are among the most common stereocenters in Nature. They form glycosidic bonds that link together essential molecules of life, carbohydrates, including starch and cellulose, the most abundant organic material on Earth. Stereogenic acetals are also common motifs in other natural products, from small insect pheromones to highly complex spiroacetal polyketides. Although far less common than O,O-acetals, chiral N,N-, N,O-, and N,S-acetals are structural motifs also found in a number of natural products and pharmaceuticals. Here, recent progress towards chiral acetals using asymmetric Bronsted acid catalysis is summarized, with particular emphasis on O,O-acetalizations. In this context the development of novel catalyst classes, namely spirocyclic phosphoric acids and confined Bronsted acids, proved crucial and is also presented.