Stereochemistry of heterocycles

Abstract

Twenty-eight previously unreported compounds of the 4,5-dialkyl-, 4,5,5-trialkyl-, 2,2,4-trimethyl-5-alkyl, and 2,2,4-trimethyl-5,5-dialkyl-1,3-dioxane series, including 24 individual cis and trans isomers, obtained with a purity of the order of 85–99% by fractionation of the starting mixtures of stereoisomers with total condensation columns, were synthesized. The applicability of the Cram rule, modified for compounds with complexforming groups, for the estimation of the possible configurations and conformations of the stereoisomers of the examined series was demonstrated. The cis configuration of the lowboiling stereoisomers and the trans configuration of the high-boiling stereoisomers were proved by NMR spectroscopy; the investigated compounds exist predominantly in the chair conformation. The 5-C-axial position is preferred over the 4-C-axial conformation in the examined series of compounds. The synthesis and hydrolysis of the examined 1,3-dioxanes proceed without involvement of the steric centers of the molecules, and the configurations of the corresponding diastereomeric 1,3-diols can be established on the basis of data on the configurations of the 1,3-dioxanes. The IR spectra of the stereoisomers of the examined series of compounds were studied, and the spectral characteristics of the trans and cis isomers, respectively, were found.