Intramolecular tetrazine-acryloyl cycloaddition: chemistry and applications.

An unprecedented intramolecular [4 + 2] tetrazine-olefin cycloaddition with α,β-unsaturated substrates was discovered. The reaction produces unique coumarin-dihydropyridazine heterocycles that exhibited strong fluorescence with large Stokes shifts and excellent photo- and pH-stability. This property can be used for reaction analysis.