Abstract
The photohydration of hydroxy-substituted 1,1-diaryl alkenes 1−3 has been studied in aqueous CH3CN solution. Evidence for formation of quinone methide intermediates was provided by product studies and by observation of its absorption spectrum by laser flash photolysis. For the meta isomers, the proposed mechanism of m-quinone methide formation probably involves a solvent-mediated (“proton-relay”) excited-state (formal) intramolecular proton transfer (ESIPT) from the phenol hydroxyl group to the β-carbon of the alkene moiety in neutral aqueous CH3CN solution, either in a concerted manner or via two very fast steps. The m-quinone methides are then trapped by water to form the corresponding diaryl ethanol product with high overall quantum yield. Evidence for the ESIPT pathway was provided by fluorescence and LFP measurements. The addition of small amounts of water (<0.8 M in CH3CN) decreased the fluorescence emissions of 1 and 2 with a concomitant increase in production of m-quinone methides. Stern−Volmer an...
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