Photochemical transformations in a water-soluble supramolecular assembly: Spatial and temporal effects on product selectivity.

摘要

This dissertation will focus on NMR studies and photochemical experiments performed in a supramolecular host-guest assembly in aqueous media. Cavity of the synthetic resorcinarene based host molecule used in this study acts as a hydrophobic pocket for guests like dibenzyl ketones, N-alkyl-2-pyridone and tropolone ethers. Two molecules of the host self-assemble to form a capsular complex in the presence of a guest. It was possible to identify the binding modes of the guest molecules inside the cavity of the host using 1D and 2D NMR spectroscopy techniques like NOESY, TOCSY and DOSY. Photochemical reactivity of the bound guest molecules were found to be different from their reaction in isotropic solutions illustrating the ability of the host to confine the guests, the intermediate radicals and the photoproducts. Additionally, unlike many other supramolecular hosts, generally less significant substituent effects were found to play a major role in the binding motif and consequently, reactivity of the guest substrates.;Dibenzyl ketones were used to probe the stability of the complex. By introducing different alkyl substituents in the para position and in the alpha-position, binding modes of the guests were altered. Their photochemical behavior correlated well with the structure established by NMR studies. Dynamic nature of the intermediate radicals bound to the guest was confirmed by formation of rearrangement products. Diastereoselective cyclization reactions of N-alkyl-2-pyridones, tropolone ethers and cyclohexadienone carboxamide appended to a chiral auxiliary were also studied. Observed selectivity in the reaction of methyl-substituted pyridones depended on position of the methyl substituent on the pyridyl ring.