Michael Addition–Aromatization Reaction of Dienylimines Bearing a Leaving Group and Its Application to the Preparation of Thiol-Selective Labeling Reagents Capable of Forming Strong Carbon–Sulfur Bonds

The reaction of a dienylimine with thiols was found to proceed smoothly to afford the corresponding indolines bearing aromatic carbon–sulfur bonds as a result of a Michael addition–aromatization sequence. Furthermore, this reaction was applied to the development of fluorogenic dienylimines that could be used as thiol-selective fluorescent labeling reagents.