Acetylenic cyclodextrins for multireceptor architectures: cups with sticky ends for the formation of extension wires and junctions

A mono-6-O-propargyl permethylated β-cyclodextrin, 3, has been prepared by two synthetic routes as a versatile building block for the construction of cyclodextrin dimers and trimers with a core junction which is potentially electron conducting. Glaser–Hay coupling of 3 gave β-cyclodextrin dimer 6, and Pd(0)-catalysed coupling allowed the preparation of a cyclodextrin dimer with a 1,4-phenylene bridge, 7, and a cyclodextrin trimer based on a 1,3,5-trisubstituted benzene, 8. All compounds have been fully characterised, and in particular, detailed analysis by 2D NMR spectroscopic techniques has provided useful insight into the identities of the compounds. The detailed full characterisation of mono-3,6-anhydro-heptakis(2,3-O-methyl)-hexakis(6-O-methyl)-β-cyclodextrin, 5, is also described. Product 5 is formed during the methylation of compound 3, and its formation was found to be sensitive to the reaction conditions. The absorption and fluorescence spectra of the phenylene-bridged dimer 7 and trimer 8 are also reported. They show different properties of the excited state based on the different electronic coupling imposed by the phenylene core.