A 25-mL round bottom flask is fitted with a magnetic stirring bar and a rubber septum and carefully flame-dried under Ar. A drying tube is fitted to the septum and $MgBr_2OEt_2$ (2.8 mmol. Make sure this reagent appears to be water free! When dry, this reagent is powdery; when wet, it forms clumps. Return to the desiccator immediately after weighing.) is quickly added. After purging the flask again with more Ar, 7.5 mL of dry (from the solvent purification system) $CH_2Cl_2$ is added to the flask by syringe. This is followed by the addition by syringe while stirring of thioester (1.5 mmol), the assigned aldehyde (1.8 mmol) and finally $i-Pr_2NEt$ (3.0 mmol). Stir the mixture for 30 min and $EtOAc$ (10 mL) and 10\% aqueous $HCl$ (10 mL) are added. Stirring is continued for a further 20 min and the mixture partitioned between $EtOAc$ (40 mL) and water (10 mL). The two phases are separated and the aqueous phase is extracted with $EtOAc$ (1 x 10 mL) and the combined organic extract is washed with brine, dried ($MgSO_4$), filtered, and evaporated to give a light-yellow solid.
