Acyloxonium ions in the high-yielding synthesis of oxolanes from alditols, hexoses, and hexonolactones catalysed by car☐ylic acids in anhydrous hydrogen fluoride

Abstract

Treatment of d-glucono-1,5- or d-mannono-1,4-lactone with anhydrous hydrogen fluoride catalysed by formic or acetic acid yields 3,6-anhydro- d-glucono- and - d-mannono-1,4-lactone, respectively. Similarly, d-mannitol is converted into 1,4-anhydro- d-mannitol and subsequently into the 1,4:3,6-dianhydride, whereas d-glucitol forms exclusively the 3,6-anhydride and, on further reaction, 1,4:3,6-dianhydro- d-glucitol. d-Glucose and 2-acetamido-2-deoxy- d-glucose are also converted into the corresponding 3,6-anhydrides by reaction with hydrogen fluoride and formic acid. 13C-N.m.r. spectroscopy indicates that the reactions involve intermediate dioxolanylium ions.