Design, Synthesis And Properties Of Inherently Chiral 1,2-alternate Calix(4)crown And 1,3- And 1,2-calix(4)crown-7 And Calix(4)crown-9 Cone Conformers

As the third generation of supermolecular host compounds after crown ethers and cyclodextrins, calixarenes have been studied a lot in the field of molecular recognition, molecular self-assembly, asymmetric catalysis and enzyme mimics. The potential application of calixarenes has been attracting researchers'increasing interest. This paper designes the synthesis of two kinds of calixarene host moleculars. The recognition and complexing capacity of the new compounds have also been studied by extraction experiments and NMR titration after the synthesis. This article consists of two parts, which focus on inherently chiral 1,2-alternate calix[4]crown and macrocyclic calix[4]crown separately.PartⅠDesign, synthesis and properties of inherently chiral 1,2-alternate calix[4]crownBesides the ready modification of the upper rim, the lower rim and even the brdiging methylene, the rich stereochemistry of calixarenes also accounts for their versatility. Compared with the other three conformers, calix[4]arenes in the 1,2-alternate conformation were less reported, mainly due to the lack of a satisfactory preparation method. Previous literatures have disclosed that t-BuOK as a base generally affords the biscalix[4]crown 1,2-alternate conformers in low to moderate yields, along with the cone conformer counterparts. On the other hand, inherent chirality can be generated in the calix[4]arene molecules by the asymmetric array of at least one achiral substituent onto its nonplanar 3-dimensional skeleton, leading to optical isomers. Inherently chiral calixarenes are receiving increasing attention due to their potential application in the fields of enantioselective discrimination and asymmetric catalysis. So far, though there have been increasing examples of inherently chiral calix[4]arenes with various substitution patterns (upper and/or lower rim, meta-position) and novel structures, most of them are cone and partial cone conformers. The scarcity of inherently chiral calix[4]arene 1,2-alternate conformers has attracted our attention and herein we report on the design and synthesis of an inherently chiral calix[4]arene in the 1,2-alternate conformation. The structure of the product was confirmed by 1H NMR, 13C NMR, MS and X-ray single crystal diffraction. The chiral separation has also been realized through the chiral reagent.PartⅡIntramolecular cyclization strategy: synthesis of 1,3- and 1,2-calix[4]crown-7 and calix[4]crown-9 cone conformers Calix[4]crowns represent a wide range of peculiar synthetic ionophores which possess both versatile calix[4]arene skeletons and crown ether moieties. Intense investigation has revealed that specific calix[4]crowns exhibit efficient and selective binding ability towards alkali metal, alkaline earth metal and ammonium cations by different substituents attached to the host. Regarding the synthesis of calix[4]crowns, intramolecular cyclization strategy has been widely applied. In this context, the most popular method features the direct condensation of calix[4]arenes and oligoethylene glycol ditosylates in the presence of appropriate base and solvent via nucleophilic substitution reaction. In view of the scarcity of the reports on the properties of calix[4]crowns containing more than 6 oxygen atoms in the crown ether units, we report a general method for the synthesis of distally- and proximally-substituted calix[4]crown cone conformers by an intramolecular cyclization strategy via simple nucleophilic substitution reaction. their binding properties towards alkali and alkaline earth metal picrates have also been evaluated by two-phase extraction experiment.