| Abstract |
The synthesis of four inherently chiral monoalkyl ethers (methyl, ethyl, allyl, and benzyl), derived from p-tert-butyldihomooxacalix[4]arene, is described. Their conformational features were studied by variable temperature H-1 NMR spectroscopy in solvents with different polarity, such as chloroform (or CDCl2CDCl2) acetone, DMSO, and pyridine. Coalescence temperatures and Delta G double dagger were determined in CDCl2CDCl2 and pyridine solutions. Monomethyl ether has a T-c of 86 degrees C in CDCl2-CDCl2 and of -8 degrees C inpyridine, and the other derivatives are conformationally immobilized (Delta G double dagger >> 20 kcal mol(-1) in both solvents). The cone conformation, obtained for all monoethers, was confirmed by C-13 and NOESY spectra and also from a series of NOE 1D experiments. Complete assignment of both proton and carbon NMR spectra was achieved for the monomethyl ether by a combination of COSY, HMQC, and selective INEPT experiments, in chloroform at room temperature. Inherent chirality for all compounds was demonstrated by the addition of Pirkle s reagent to CDCl3 solutions of monoethers derivatives, causing duplication of the NMR proton signals. |
