Photochemical Formation of Dibenzosilacyclohept-4-yne for Cu-Free Click Chemistry with Azides and 1,2,4,5-Tetrazines

Photochemical generation of dibenzosilacyclohept-4-yne 3 from the corresponding cyclopropenone 1 and its copper-free click reactions are reported. Steady-state irradiation, kinetic, and transient absorption spectroscopy studies revealed that strained alkyne 3 is rapidly (<5 ns) and efficiently (Φ = 0.58–0.71) photoreleased from 1 and undergoes remarkably fast, selective, and high-yielding 1,3-dipolar cycloaddition with benzyl azide (∼20 M^–1 s^–1) or [4 + 2] inverse-electron-demand Diels–Alder reaction with 1,2,4,5-tetrazines (∼260 M^–1 s^–1) in both methanol and acetonitrile.