Synthesis and Molecular Recognition of Spherand-type Calixarenes

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1.The development of synthesis of sperand-type calixarenes We have succeeded to develop a convenient and selective synthesis of a series of hydroxy[1_n]metabiphenylophanes with three and four biarene units involving base-catalyzed condensation of 5,5'-di-tert-buty1-2,2'-dihydroxybiphenyl with formaldehyde under xylene reflux depending on the alkaline metal hydroxide as a base.2.Studies on reactivities and propcties Electrophilic aromatic substitution reactions and O-alkylation of phenolic oxygenes of the spherand-type calixarenes were studied in order to increase the binding abilities for the guest molecules. The influence of O-substituents on the conformational isomerism has been established. Introduction of larger alkyl groups on the phenolic oxygens should lead to a situation where the OR groups within a biarene unit cannot pass each other. That means the rotation around the Ar-Ar sigma-bond is hindered and each biarene unit is fixed in a certain configuration. For example, in the c … More ase of the tetramer four different diastereomers of which two are chiral should be expected : a)A compound in which all biarene units have the same configuration (RRRR or SSSS,D_4-symmetry) ; b)A compound in which the configuration of one biphenyl unit differs from that of the other three(RRRS or SSSR) ; c)(RSRS=SRSR) ; or d)(RRSS=SSRR).3.Studies on molecular recognitions We have demonstrated for the first time that the derivatives of the spherand-type calixarenes formed by alkylation with ethyl bromoacetate give ionophores with promising complexation properties for metals and ammonium ions and interesting stereochemistry. These compounds are found to have combined properties of both the spherands and the calixarenes. Thus the restricted ring conformation due to the biarene units may increase the selectivity in the binding of metal ions as compared to the same functionalized phenolic units in calix[6]arene and calix[8]arene. While to date only two stereoisomers have been obtained, variation of the alkylation conditions and reagents could lead to the derivatives with D_3-and D_4-symmetry, which will serve as interesting building blocks for larger potential host molecule such as chiral recognitions. Less