An investigation into the synthesis and structure of cyclic butylidene acetals

Abstract

The acid catalysed condensation reactions of various polyhydroxyl compounds and n-butyraldehyde have been investigated.

Initially these reactions have been examined to determine whether kinetic control was exhibited during the mono acetalisation stages. The products of these polyols, including diacetals, have been isolated and characterised.

For the polyols examined L-threitol, D-arabinitol and 6-deoxy-D-glucitol gave kinetic control (all of these polyols contained an alphaT configuration of hydroxyl groups which had previously been confirmed to facilitate kinetic control). The kinetic acetals isolated contained the 2,3 structure.

Erythritol, ribitol, xylitol and l-deoxy-D-xylitol did not give kinetic control (n.b. xylitol and 1-deoxy-D-xylitol contained an alphaT hydroxyl group configuration).

The thermodynamic acetals isolated contained the 2,4 (betaC) ring or alternatively the 1,3 (beta) ring in accord with the rules of Barker and Bourne.

Diacetals were isolated for erythritol, L-threitol, ribitol, xylitol, 1-deoxy-D-xylitol and 6-deoxy-D-glucitol. A mixture of diacetals was produced by D-arabinitol, which could not be separated.

Acetalisation of methyl alpha-D-glucoside was considered in non-aqueous solution: kinetic control was not exhibited. The 4,6 acetal was isolated as the thermodynamic mono acetal, and methyl 2,3 oxidodi- n-butylidene 4,6-O-butylidene alpha-D -glucoside from the reaction with excess n-butyraldehyde.

Ultimately pentaerythritol and dipentaerythritol were examined: a mono acetal was isolated for penta erythritol whereas both formed diacetals.

The structures of the previously mentioned acetals were confirmed by chemical techniques, where possible.

All of the acetals have been subjected to a spectroscopic examination. This has aided the structural assignments of fully substituted polyol acetals.

Mass spectrometry of the diacetals has shown the 'h-rupture' fragmentation mechanism.

Two nuclei have been considered for nuclear magnetic resonance spectroscopy: 1H and 13C.

For proton magnetic resonance spectroscopy the correlation between the resonance of the acetal proton and ring size has been confirmed. Similar inferences have been concluded for the resonance of the acetal carbon atom and the acetal ring size for carbon magnetic resonance spectroscopy.