Vinylidene–Quinone Methides, Photochemical Generation and β-Silicon Effect on Reactivity

Irradiation of 2-alkynylphenols resulted in the generation of vinylidene–quinone methides (QMs), which were detected by laser flash photolysis in organic solvents and aqueous acetonitrile. QMs' spectroscopic properties and electrophilicity were both significantly affected by β-silicon effect. The hydration of the alkynyl moiety (22 and 900 M–1 s–1 for QM-1 and QM-2, in aqueous acetonitrile) was an acid- and base-catalyzed process. The addition of amines was fast (9.2 × 103 M–1 s–1 < k 2 < 1.3 × 108 M–1 s–1), yielding ketimines, with primary amines.