Syntheses And Planar Chirality Of Rigid-Pillar[5]arene Dimer-based Rotaxanes

Pillararenes are a type of novel macrocycles,which are made up of hydroquinone or hydroquinone ether derivatives and connected by methylenes at para-positions.Planar chiral pillararenes have potential applications in asymmetric catalysis,artificial transmembrane channels,molecular universal joint,etc.However,due to the free rotation of paraphenylene methylene units,pillar[5]arenes with small substitution groups have eight conformational isomers which can be freely inverted in solution.Therefore,just a few planar chiral pillar[5]arenes were reported until now.Inhibition of the rotation unit can lock the conformation and afford planar chirality.In this dissertation,a new type of rigid pillar[5]arene dimers(P[5]D)bridged by oxacalix[4]arene were designed and synthesized.Because of the steric hindrance of oxacalix[4]arene framework,the conformation of two pillar[5]arene rings is fixed to form planar chirality.Furthermore,rotaxanes were constructed and their planar chirality and isomerization were investigated.The main contents are as follows:In the first part of this thesis,using A1/A2 dihydroxylated pillar[5]arene and1,5-difluoro-2,4-dinitrobenzene as reagants,two products 1a and 1b were synthesized via both one-pot and two-step fragment-coupling approaches,respectively.~1H NMR and HRMS indicated that 1a and 1b are pillar[5]arene dimeric isomers.X-Ray single crystal analysis of 1b showed that oxacalix[4]arene-bridged pillar[5]arene dimer has a shape of a telescope and can be self-assembled into two interesting pentagonal channel in the solid state.Chiral HPLC experiments and CD spectrometry confirmed that 1a and 1b were diastereomers of P[5]D,in which 1a was a racemic mixture and1b was an achiral mesomer.The two fractions S_p-S_p-1a and R_p-R_p-1a could be further resoluted by the preparative chiral HPLC.The planar chirality of P[5]D provide opportunities to construction of chiral mechanically interlocked structures.In the second part of this thesis,P[5]D 1a can be further associated with semi-blocked rod-like alkane compound 5 and formed pseudorotaxane.The complexation stoichiometry between 1a and 5 was 1:2 in chloroform-d at room temperature.Using a snapping method,[2]rotaxanes and[3]rotaxanes were successfully obtained by reacting 1a or 1b with 5 respectively.X-ray crystal analysis and chiral HPLC experiments indicated that[2]rotaxanes have two pairs of enantiomers GR_p-R_p-2a and S_p-GS_p-2a,GR_p-S_p-2b and R_p-GS_p-2b;[3]rotaxanes have one pair of enantiomers GR_p-GR_p-3a and GS_p-GS_p-3a,and a mesomer GR_p-GS_p-3b.Our findings will deeply enhance the understanding of planar chirality of pillar[5]arene derivatives and their chiral rotaxanes,which will in turn guide our design for new chiral functional supramolecular systems.