Reaction of Isatin and 2-Chloropyridinium Salt: An Efficient and Diastereoselective Synthesis of α,β-Unsaturated Oxindoles

A new, mild, and diastereoselective method has been developed for the synthesis of β-pyridone-α,β-unsaturated oxindoles by the reaction of isatins and 2-chloropyridinium salts in EtOH at room temperature for 5 min. This method operates under mild reaction conditions, providing the product with a good yield and diastereoselectivity, and it exhibits excellent tolerance toward various functional groups. The predominant isomer is the <i>Z</i> isomer, which can convert to the <i>E</i> isomer in the presence of NaN₃.