[3,3]Claisen vs. [2,3]Wittig Shift in Thermal and Fluolide Ion-Promoted Rearrangements of the O- and C-Silylated Forms of α-Allyloxy Esters

Thermolysis of the O-silylated forms of α-allyloxy esters is shown to afford exclusively the [3,3]Claisen products with high stereocontrol. In direct contrast, the fluoride ion-promoted rearrangement of the α-silylated esters gives exclusively the [2,3]Wittig products with moderate stereocontrol.