STERIC AND ELECTRONIC EFFECTS IN CONFORMATIONAL PREFERENCES OF C1-OXYGENATED CHIRAL ALKENES

A variable temperature NMR study shows that the benzyl protective grou p on the hydroxy function of a chiral allylic alcohol enhances the CH eclipsed form (I). On the other hand, various silyl ethers enhance the preference for the CO eclipsed conformer. However, when both the ally lic R group and the hydroxy protective group are bulky (R tert-butyl, P = TIPS), the staggered conformation of the chiral alkene becomes pre ferred. An acetate group does not have an apparent effect on the confo rmational preference of the protected allylic alcohol. These facts are explained in terms of steric and electronic interactions.