Isobutylidenation of 1-C-substituted polyols. Attempted extension of the NMR shift rule via the chemical shift difference of their two methyl groups

The isobutylidenation of 1-C-substitutedl-threo-, d-erythro-glycerols, and d-arabino-tetritol has been studied. The location of the acetal could be adjusted by selecting the conditions for acetalation as well as the configuration of the polyol. The structure of the products was deduced by a combination of physical and chemical methods. The shift rule for the isopropylidene group has been extended to include the chemical shift difference of the two methyl groups of the isobutylidene rings.