Eine einfache Darstellung von I .3-Dioxolan-ylium-(2)-SbCl~-und 1.3-Dioxan-ylium-(2)-SbCl6-SalZeJl ist durch Einwirkung von SbCIS auf 1.2-bzw. 1.3-Diolester moglich. Von cyclischen 1.2-und I .3-Diolestern der Cyclopentan-und Cyclohexanreihe reagieren nur die trans-Verbindungen, da die SbCI~-katalysierte Saure-Anion-Ablosung der Nachbargruppenunterstiitzung bedarf. cis-Verbindungen liefern mit SbCIs Addukte. I n fliissigem H F reagieren von den cyclischen 1.2-Diolestern umgekehrt nur die cis-Verbindungen zu Acyloxonium-Verbindungen. Tetra-O-acetyl-(l.2/3.4)-cyclopentantetraol (30) bildet in fliissigem H F ein Dikation 31. Carboxonium Compounds in Carbohydrate Chemistry, XI1
Synthesis of Acyloxonium Salts of 1 .Z-Diols and 1.3-Diols
The reaction of SbCIs with 1.2-or 1.3-diol esters serves as a simple method for the preparation of 1 .3-dioxolan-2-ylium-SbC16and 1.3-dioxan-2-ylium-SbCl~ salts, respectively. From cyclic 1.2-and 1.3-diol esters of the cyclopentane and cyclohexane series reaction is found for the trans-compounds only, since the SbCIpxtalyzed carboxylate ion abstraction proceeds by way of neighboring group participation. cis-Compounds form SbCIS adducts. Contrarily, in liquid hydrogen fluoride only the cis-compounds of cyclic 1.2-diol esters undergoe reaction to form acyloxonium compounds. Tetra-O-acetyl-(l.2/3.4)-cyclopentanetetraol (30) forms the dication 31 in liquid hydrogen fluoride.