Synthesis and Host–Guest Properties of Acyclic Pillar[n]naphthalenes

Here we report a new class of synthetic receptors, acyclic pillar[n]naphthalene (n = 2–4, Dimer, Trimer, and Tetramer) oligomers, which are made up of 2,3-diethoxynaphthalene units linked by methylene bridges at the 1- and 4-positions. They can be synthesized through a one-step condensation of 2,3-diethoxynaphthalene monomer and paraformaldehyde in the presence of BF(3)•(Et)(2)O catalyst. The crystal structure of Tetramer has an interesting pseudo-cycle shaped structure in the solid state. Their complexation behaviors toward several organic ammonium cations (1(+)-15(+)) and electron–deficient neutral guests (16–17), were examined by means of (1)H NMR spectroscopy. Tetramer shows good host-guest properties toward the ammonium guests, giving association constants (K(a)) in the magnitude of 10(2)-10(4) M(−1), which are comparable with those for some macrocyclic hosts.