We
herein report the synthesis of novel “Janus” calix[4]arenes
bearing four “molecular tethering” functional groups
on either the upper or lower rims of the calixarene. These enable
facile multipoint covalent attachment to electrode surfaces with monolayer
coverage. The other rim of the calixarenes bear either four azide
or four ethynyl functional groups, which are easily modified by the
copper(I)-catalyzed azide–alkyne cycloaddition reaction (CuAAC),
either pre- or postsurface modification, enabling these conical, nanocavity
reactor sites to be decorated with a wide range of substrates to impart
desired chemical properties. Redox active species decorating the peripheral
rim are shown to be electrically connected by the calixarene to the
electrode surface in either “up” or “down”
orientations of the calixarene.
The preparation of a series of new prochiral bis-alkynes is reported. A selection of chiral ligands is examined to gain additional information about the scope of the new asymmetric Huisgen 'click' reaction [the desymmetrisation of bis-alkynes using chiral ligands in conjunction with the widely applied copper-catalysed azide-alkyne cycloaddition (CuAAC) triazole synthesis]. The development of a new chiral assay for (±)-methyl 2-[(1-benzyl-1H-1,2,3-triazol-4-yl)methyl]-2-cyanopent-4-ynoate, and the production of this mono-triazole in up to 18% enantiomeric excess is described.
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