Temperature effects on stereocontrol in the Horner-Wadsworth-Emmons condensation of alpha-phosphono lactones.

The Horner-Wadsworth-Emmons condensation of some alpha-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 gamma-butyrolactone was treated with potassium hexamethyldisilazane, 18-crown-6, and propionaldehyde at -78 degrees C in THF, an aliquot transferred to a flask at approximately 30 degrees C gave almost exclusively the Z-olefin product, while one allowed to warm to room temperature over several hours greatly favored the E-olefin.