A novel crown ether generation containing the pyrilium heteroaromatic cation — Synthesis, characterization, and solid-phase 13 C NMR

The synthesis and structural characterization of two members, 5 and 6, of a novel generation of crown ethers containing the pyrilium cation are reported. These two compounds contain two and three benzo-9-crown-3 (B9C3) units, respectively, connected to the 2 and 6 or 2, 4, and 6 positions of a central pyrilium cation. The crown ethers 5 and 6 were obtained from the condensation reaction of appropriate aldehydes and methyl ketones in the presence of POCl 3 . A variety of physicochemical methods including electrospray mass spectroscopy, solution 1 H and 13 C NMR, and solid-phase 13 C NMR were applied for structural characterization. The 1 H and 13 C NMR studies indicate rapid rotation of the B9C3 unit about the C–C bond that connects the two units to each other. The solid-phase 13 C NMR spectra of these two crown ethers reveal that there are deviations from planarity for the two phenyl rings attached at the 2 and 6 positions of the central pyrilium cation.Key words: crown ether, pyrilium, solid-phase NMR, crownpyrilium, heteroaromatic.