Stereochemistry and NMR spectra of some new unsymmetrical substituted 2,2-dialkyl-1,3-dioxanes

New anancomeric 1,3-dioxanes were obtained by the ketalization reaction between unsymmetrical ketones and 1,3-diols obtained from esters of the malonic acid and formaldehyde. The anancomeric structures of the compounds were proved by their H-1 and C-13-NMR spectra. The compounds have an axial methyl group in the 2-position which determines the steric compression of the axial hydrogens located to the C-4,C-6 atoms having as a result their significant deshielding, respectively a very small difference between the chemical shifts of the equatorial and axial protons. Their assignment was made by means of a NOE experiment. The influence of solvents upon chemical shifts was also mentioned (ASIS effect).