1,3-DIOXENIUM CATIONS - SYNTHESIS, STRUCTURE AND TOPOMERIZATION

Previously unknown 1,3-dioxenium perchlorates were obtained by couplin g 1,3-diketones with aliphatic ketones in an acetic acid solution of p erchloric acid. The dioxenium ring of thoxystyryl)-2,2-pentamethylenes piro-1,3-dioxenium perchlorate in the crystal possesses the envelope c onformation, the geometry of the carbon triad being close to that of t he allyl cations. Variable-temperature H-1 NMR spectra of unsymmetrica l 1,3-dioxenium cations revealed the occurrence of a sufficiently fast enantiotopomerization process governed by the C-O bond dissociation-r ecombination mechanism.