Thermal epimerization of inositol 1,3-benzylidene acetals in the molten state

1,3-O-Benzylidene-2,4,5,6-tetra-O-substituted-myo-inositol derivatives obtained by the DIBAL-H reduction of the corresponding myo-inositol 1,3,5-orthobenzoate derivatives undergo epimerization at the acetal carbon on heating, in the molten state, just above their melting point. The same epimerization reaction does not proceed either in the crystalline state or in solution. DFT calculations suggest that the epimeric acetal obtained by this thermal process is relatively more stable than the starting acetal. Either of these acetals could not be obtained by the reaction of the corresponding inositol derived diol with benzaldehyde. These observations constitute a novel reaction solely in the molten state, which are rarely encountered in the literature. X-ray crystal structures of the epimeric acetals as well as their radical deoxygenation reaction are also reported.

Certain 1,3-benzylidene acetals of inositols undergo epimerization at the acetal carbon when melted. This epimerization does not occur in the solid state or in solution. These results suggest that in the molten state aggregated molecules achieve the fine balance between the rigidity of the matrix, and the molecular motion needed for their reaction.Figure optionsDownload as PowerPoint slide