AbstractsChemistry

The general concept of developing gateable host-guest systems is a powerful one with many potential applications such as drug delivery and sensing. In this work, we designed and synthesized a reversible photoswitchable hemicarcerand. This hemicarcerand has an anthracene unit as the photoactive gating element and the reversible opening and closing of the "gate" of the host is well controlled photochemically. Various spectroscopic methods such as 1H NMR and fluorescence demonstrate that, hemicarcerand host-guest complexes are stable to decomplexation at ambient temperatures in the photodimer structure, while release of guests such as 1,4-dimethoxybenzene is achieved by opening the gate by photochemically generating the anthracene monomers.The second part of this dissertation involves the use of computational chemistry to understand the origins of stereoselectivity in synthetically useful reactions. In collaboration with Prof Wicha's group in Poland, alkylation reactions of azulenone precursors in the guanacastepene A synthesis were studied and steric effects were determined as the origins of different stereoselectivities observed experimentally. Next, in collaboration with Prof Jung's group in UCLA, an unusual conformational effect on reactivities in a cyclic non-aldol aldol rearrangement was explained using theoretical models. In collaboration with Prof Overman, the stereoselectivities of the dihydroxylations of cis-bicyclo[3.3.0]octene intermediates for total synthesis of chromodorolide A were investigated and torsional effects were identified as the control elements here. Other related examples from the literatures were also studied and it was found that the stereoselectivity was greatly affected by the rigidity or flexibility of conformations of reactants. Finally, in collaboration with Prof Antilla, a theoretical study of chiral Brønsted acid-catalyzed allylboration and propargylation reactions was performed. The general reaction mechanisms involving two different models were investigated, and the steric repulsions between the bulky 3,3'-substituents in the catalyst and the substrates were determined to be responsible for the enantioselectivities.