 The carbanion is generated by direct lithiation of moderately acidic substrates, tin transmetallation, or reductive lithiation of O,S-acetals.Stereoselective methods employing chiral starting materials have been used to effect either asymmetric induction or simple diastereoselection

After carbanion formation, the [2,3]-Wittig rearrangement is rapid and selective at low temperatures.However, if the reaction mixture is allowed to reach temperatures above −60 °C, [1,2]-rearrangement becomes competitive.