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1、3MolecularBaskets,ChalicesandCages3.1OneforBeginnersThefacilecondensationreactionbetweenformaldehydeandphenolsortheirderivativesprovidesamajorrouteintorigidmacrocyclesusedinsupramolecularchemistry.Calixarenes,thebest-knownclassofphenol-derivedmacrocycles,arep
2、reparedthisway,asarespherandsandtheirrelatives.Cyclotriveratrylene,however,isanexcellentexemplarofthemolecularbaskettypeofligandandhasbeenknownforthebestpartofacentury.ThebasiccyclotriveratrylenesynthesisisshowninFigure3.1.TheoriginalprocedurebyMrs.GertrudeMa
3、udRobinson[1]hassincebeenrefinedbyothersandmanyvariationsareknown[2,3].Despitetheearlydiscoveryofcyclotriveratryleneittookuntil1965foritsstructuretobedeterminedbynuclearmagneticresonance(NMR)[4].Asolvatedcrystalstructureonlyappearedin1979[5]anditwasafurtherdec
4、adebeforethesolvent-freestructurewasreported[6].ManyderivativeshavebeenpreparedandsomeexhibitusefulinclusionpropertiessuchasthatinFigure3.2.ThesynthesisincludedhereisbasedonthatreportedbyRobinson.Inherpaperthestructureofthecolourlesscrystallineprecipitateresu
5、ltingfromthecondensationofveratrolewithformaldehydeinsulphuricacidwasgivenadimeric,ratherthantrimeric,configuration.Atthetimetheproductwasbelievedtobe2,3,6,7-tetramethoxy-9,10-dihydroxyanthracene;however,asthiswasdeterminedbythepercentageofcarbonandhydrogenint
6、hecompounditisanunderstandableerrorasthecompositionwouldbethesameforanyhigherhomologue.Theprocedureistheresultofmuchtrialanderrortogetherwithcarefulobservation:aswillbeseenfromtheliteraturesurroundingacid-catalysedreactionsbetweenaldehydesandphenols(ortheirde
7、rivativessuchasresorcinol,APracticalGuidetoSupramolecularChemistryPeterJ.Cragg#2005JohnWiley&Sons,LtdISBN:0-470-86653-570MOLECULARBASKETS,CHALICESANDCAGESMeOOMeOMeH2SO4,H2CO,OMeethanolMeOOMe23MeOOMeFigure3.1Synthesisofcyclotriveratrylene(23)Figure3.2Structure
8、ofacyclotriveratryleneinclusioncomplexpyrogallolandveratrole),yieldsarehighlyvariable.Colletsreview[2]lists15setsofconditionsthatgivebetween21and89percentyieldand,oftheseexamples,sixaresi
