Nucleophilic substitution in glycerol derivatives. Part VI. Halogenodeoxygenation of 2-phenyl-1,3-dioxan-5-ol to give 1,3-dioxans and 1,3-dioxolans

Abstract

The reaction of cis-2-phenyl-1,3-dioxan-5-yl toluene-p-sulphonate with lithium bromide in boiling acetonitrile gives trans-5-bromo-2-phenyl-1,3-dioxan as the brominated product. However, the reaction between cis-2-phenyl-1,3-dioxan-5-ol and triphenylphosphine–carbon tetrabromide yields three products, cis-4-bromomethyl-2-phenyl-1,3-dioxolan, its trans-diastereoisomer and trans-5-bromo-2-phenyl-1,3-dioxan, in the proportions 45 : 48 : 7, respectively; the corresponding reaction with carbon tetrachloride gives the chloro-analogues of the three products. These rearrangements under essentially neutral conditions suggest that greater caution should be exercised in the use of acetal derivatives of glycerol as intermediates in the synthesis of pure glycerides.