Fig. 4: Reaction of 2a with ethanethiol (7a) and the time course of fluorescence in the reaction.

a TAP-VK1 (2a) smoothly reacted with ethanethiol (7a) to afford the more highly fluorescent 3a in good yield, and 2a did not react with amine and alcohol. b The fluorescence color of the reaction in dichloromethane changed to green from yellow after 5 min, and the fluorescence intensity increased with the time course and reached a maximum at 50 min (exited at 370 nm in CH2Cl2). TMG, 1,1,3,3-tetramethylguanidine.