Noncovalent Control of β-Cyclodextrin over Shapeshifting Molecules

Abstract

Fluxional carbon cages, such as bullvalene, barbaralane and the barbaralyl cation, exhibit their shapeshifting properties through the rapid Cope rearrangements which give thousands of degenerate isomers. When interacting with different guests through covalent modification or noncovalent bonding, the equilibrium distribution of isomers could be shifted, and this property can be utilized in molecular sensing. Barbaralanes only have two isomers, which makes it easier to control and investigate their dynamic equilibria. 9-Substituted barbaralanes, such as barbaralol, possess a dynamic sp3-carbon stereocentre which is similar to an inverting nitrogen center.
This thesis involves two parts, the first part is synthesis of carbonyl derivative barbaralone.Barbaralone is an important building block for the synthesis and modification of various barbaralane derivatives. However, the modern synthetic route of barbaralone with gold(I) catalyst is expensive. We aim to integrate and optimize the traditional ways and expect to get large scale of barbaralone with a lower cost.
The second part is the noncovalent control over 9-substituted barbaralanes using β-cyclodextrin and its derivatives. Our hypothesis is that, after noncovalent control of β-CD, the equilibrium distribution of barbaralanes should be pushed towards one of the two stereoisomers. In the previous work of the group, after the tolyl barbaralol 2.19 was capsulated by β-CD, the complex appeared as a head-to-head dimer in solid state with one R- and one S- isomer in the two CD cavity. This kind of racemic self-sorting in a homochiral environment was unexpected. To further investigate this phenomenon, we aim to synthesize a β-CD dimer and use it to capsulate 2.19 and observe its effect.