engleski

Photochemical Formation and Chemistry of Long-Lived Adamantylidene-Quinone Methides and 2-Adamantyl Cations

Hydroxymethylphenols strategically substituted with 2-hydroxy-2-adamantyl moiety, AdPh 8-10, were synthesized and their photochemical reactivity investigated. On excitation to the singlet excited state AdPh 8 undergoes intramolecular proton transfer coupled with a loss of H2O giving quinone methide 8QM. The presence of 8QM has been detected by laser flash photolysis (CH3CN-H2O 1:1, τ = 0.55 s) and Uv-vis spectroscopy. Singlet excited states of AdPh 9 and 10 in the presence of H2O dehydrate giving 9QM and 10QM. Photochemically formed QMs are trapped by nucleophiles giving the addition products (e.g. Φ for methanolysis of 8 is 0.55). In addition, the zwitterionic 9QM undergoes an unexpected rearrangement involving transformation of the 2-phenyl-2-adamantyl cation into the 4-phenyl-2-adamantyl cation (Φ ~ 0.03). Analogous rearrangement was observed with methoxy derivatives 9a and 10a. Zwitterionic 9QM was characterized by LFP in 2, 2, 2-trifluoroethanol (τ = 1 μs). In TFE, in the ground state, AdPh 10 is in equilibrium with 10QM, which allowed for recording 1H and 13C NMR spectrum of the QM. Introduction of the adamantyl substituent into the o-hydroxymethylphenol moiety increased the quantum yield of the associated QM formation by up to 3-fold and significantly prolonged their lifetimes. Furthermore, adamantyl substituent made the study of the alkyl substituted quinone methides easier by LFP by prolonging their lifetimes and increasing the quantum yields of formation.

adamantanes; 2-adamantyl cations; laser flash photolysis; photochemistry; proton transfer; quinone methides; rearrangement; solvolysis

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