| A stereoselective reaction between resorcin[4]arenes with benzal bromides was developed in an effort to extend the π-surface of cavitands. During the formation of eight C-O bonds between five molecules, the stereoselectivity for each bridge was found to be as high as 87%. The C4v symmetry structure of the first deep-cavity cavitand (DCC) was confirmed by X-ray crystallography.; The same strategy could be utilized in the synthesis of various functionalized deep-cavity cavitands. It was observed that the reaction was sensitive to the functional groups in the bridging material. Strong electron-withdrawing groups (X = CN, NO2, CO2Et) diminished the reaction yield, while less strong electron-donating or -withdrawing groups (X = Me, Br, I, Ph) had little influence on the reaction. However, for those reactions with strong electron-withdrawing groups, the reaction could be improved by combination of the stronger homogeneous base, diazabicyclo[5.4.0]-unde-7-ene (DBU), slower addition of the bridging material and increased reaction time.; To investigate the self-assembly of these derivatives, the synthesis of two benzyl alcohol DCCs from the corresponding tetrabromo deriving DCC was also undertaken. The 2- and 3-benzylic alcohol DCC derivatives were prepared by formylation of the Br-substituted DCCs, followed by reduction with NaBH 4. The synthesis of the corresponding 3,5-octol was also investigated. Bridging reaction of resorcin[4]arenes with dimethyl 5-(α,α-dibromomethyl)isophthalate, followed by LiAlH4 resulted in the (octol) 3,5-benzylic alcohol DCC derivative. Self-assembly of the 2-, 3- and the 3,5-benzylic alcohol DCCs under standard condition (DMSO as solvent, KOBut as base, CH 2BrCl as linker reagent) afforded different products. The results were highly dependent on the structure of subunits involved in the process. For example, the 2-benzylic alcohol derived DCC only gave intramolecular bridging monomer in 59% yield, while 3-benzylic alcohol derived DCCs produced monomer, dimer and trimer in 29%, 1%, and 1% yields respectively.; Using the Ullmann reaction, it was possible to synthesize two ‘half-basket’ shaped DCCs. The binding affinity of these two half-basket DCCs, and the ‘monomers’ from self-assembly reactions for alkyl halides was measured by NMR titration. The binding affinities correlated with the structure of the DCCs. One monomer and the resorcinol half-basket DCC, showed affinity toward alkyl iodides, while the ‘monomer’ whose cavity was potentially filled with methylene groups and the large naphthalene half-basket DCC did not complex with alkyl iodides. |
