ENANTIOSELECTIVE CATALYSIS INSIDE RESORCIN[4]ARENE HEXAMER AND ITS DERIVATIVES

Molecular capsules can serve as enzyme mimetics enabling catalytic conversion of substrates inside the enclosed cavity. Supramolecular host XII self assembles via hydrogen bonds from six resorcin[4]arene building blocks 9b, and has an internal volume of 1400 Å3. Due to its highly dynamic nature, XII can reversibly encapsulate guest molecules and facilitate numerous reactions.
Some of the reactions involving cationic intermediates require HCl as a co catalyst to occur inside hexameric capsule XII. However, the effect of the acid additive has never been investigated for capsule induced iminium co catalyzed 1,4 reduction of α,β unsaturated aldehydes. In the course of this work, we examined the influence of HCl and other additives on the reaction and revised the reaction conditions. Of particular interest is the positive effect observed for alcohol additive, which proved to be beneficial for this transformation inside XII. The optimized reaction conditions allowed to reach enantioselectivity of up to 92% ee.
Additionally, we investigated the possibility of the direct chirality transfer inside similar to XII molecular capsules. Two different ways of introducing chirality on the resorcin[4]arene were explored. All of the obtained derivatives proved to self assemble in solution into hexameric capsules. These potentially catalytically active systems were further tested in terpene cyclization reactions. In this work, we report the first examples of optically active hexameric resorcin[4]arene based capsules and their ability to asymmetrically catalyze tail to head terpene cyclization reactions delivering up to 62% ee.