Temperature Effects on Stereocontrol in the Horner−Wadsworth−Emmons Condensation of α-Phosphono Lactones

The Horner−Wadsworth−Emmons condensation of some α-phosphono lactones has been examined for conditions that impact product stereochemistry. The temperature employed to quench the reaction was found to be a major factor. For example, after the diethyl phosphonate derivative of γ-butyrolactone was treated with potassium hexamethyldisilazane, 18-crown-6, and propionaldehyde at −78 °C in THF, an aliquot transferred to a flask at ∼30 °C gave almost exclusively the Z-olefin product, while one allowed to warm to room temperature over several hours greatly favored the E-olefin.