Regio- and diastereoselection in the oxaziridinium salt oxidation of acyclic allylic acetates

Oxaziridinium salt 1 is a versatile oxygen transfer agent towards olefins. An important threo selectivity is observed with acyclic allylic acetates due to 1,3-allylic strain (A1,3). The π-facial selectivity in the epoxide formation is interpretated as a consequence of an interaction between the residual positive charge on nitrogen and the neighbouring acetate in the transition state. Such an interaction is not strong enough to balance the lowered nucleophilicity of the 2,3 double bond in the geraniol acetate 3a.