p-Toluenesulfonyl Chloride

Typical Procedure (Enol Tosylation of α-Formyl Esters) Method A: An α-formyl ester (1.00 mmol) in toluene (1 mL) and TsCl (228 mg, 1.20 mmol) in toluene (1 mL) are successively added dropwise to a stirred solution of N-methylimidazole (NMI) (99 mg, 1.20 mmol) and Et3N (121 mg, 1.20 mmol) in toluene (1 mL) at 0－5 °C under an Ar atmosphere, and the mixture is stirred at the same temperature for 1 h. Water is added to the mixture, which is extracted twice with AcOEt. The combined organic phase is washed with brine, dried (Na2SO4), and concentrated. The residue is purified by SiO2 column chromatography (hexane : AcOEt = 25 : 1－5 : 1) to give the desired (E)-enol tosylates. Method B: An α-formyl ester (1.00 mmol) in toluene (1 mL), TsCl (228 mg, 1.20 mmol) in toluene (1 mL), and NMI (99 mg, 1.20 mmol) are successively added dropwise to a stirred suspension of LiOH powder (anhydrous; 29 mg, 1.20 mmol) in toluene (1 mL) at 0－5 °C under an Ar atmosphere, and the mixture is stirred at the same temperature for 1 h. A workup similar to that of method A gives the desired (Z)-enol tosylates.