Synthesis and properties of 1,3-dioxanium salts (review)

Abstract

Syntheses, structures, spectral characteristics, and chemical properties of 1, 3-dioxanium salts are reviewed.Salts of 1,3-dioxanium and 1,3-dioxolanium are unique class of nonaromatic cyclic carbonium compounds that have a positive charge on the meso-carbon atom of the O-C § fragment. The presence of the stabilized carbocation makes acyloxonium salts as convenient models for studying the reactivity and behavior of carbenium ions. Salts of 1,3-dioxolanium have been studied more than those of 1,3-dioxanium. Until recently, this was due to their greater stability and convenient synthetic method by acylation of pinacone hydrate with acylium perchlorates [1]. Recent reports indicate that the reactivity of salts with similar structures differ depending on the presence and position of substituents in the five-or six-membered rings. Salts of 1,3-dioxanium are preferred over those of 1,3-dioxolanium. o~o o~oThe review by Pittman et al.[2] on nonaromatic 1,3-heterocarbenium ions (1,3-dioxolanium, 1,3-dioxanium, 1,3-oxathiolanium, 1,3-thiolanium, 1,3-thianium, 1,3-oxathianium, 1,3-thiazolinium, 1,3-oxazolinium) contains data on 1,3-dioxanium salts only up to 1970 inclusive. Data concerning the salts of 1,3-dioxanium and 1,3-dioxolanium have recently been significantly expanded and reviewed [1]. Therefore, the aim of the present review is to supplement, generalize and systematize existing data on syntheses, structures, spectral characteristics and properties of 1,3-dioxanium salts. Certain new data on 1,3-dioxolanium salts are included for comparison. SYNTHESIS OF 1,3-DIOXANIUM SALTS1,3-Dioxanium cations were considered to be unstable intermediates in the chemistry of oxygen-containing compounds for a long time [3][4][5][6][7][8][9].From 1,3-dioxanes. For the first time in 1958 Meerwein successfully isolated crystalline 1,3-dioxanium salts, the carbonium system of which was stabilized by an inorganic anion. Thus, he subjected the starting reactant 2-ethoxy-4-methyl-1,3-dioxane to the action of an acceptor BF3"Et20 or SbCI5 [9].