PHOTOSOLVOLYSIS OF 9-FLUORENOL DERIVATIVES IN AQUEOUS-SOLUTION - EXPLORATORY STUDIES OF REACTIVITY OF PHOTOGENERATED 9-FLUORENYL CATIONS

The photosolvolysis of several 9-fluorenol derivatives (4-7) substituted at the 9-position has been studied in aqueous CH3CN and CH3OH solutions. The purpose of the study was to examine structure reactivity for photodehydroxylation of 9-fluorenol derivatives, giving rise to 9-fluorenyl cations, and subsequent chemistry of these photogenerated cations, which are formally anti-aromatic in the ground state. Derivatives 4-7 all photodehydroxylated efficiently, as measured by quantum yields for methyl ether formation. The photogenerated 9-fluorenyl cation from compound 4 also undergoes efficient E1 reaction, to give alkene 10. However, the corresponding pathway for compound 6 was inefficient due to the inability of the adjacent proton to line up in a periplanar arrangement with the empty p(z) orbital, as indicated by molecular mechanics (MMX) calculations. Photolysis of 9-vinyl-9-fluorenol (compound 5) in aqueous CH3CN gave 9-methylenefluorene derivative 20 via a simple isomerization, showing that the initially photogenerated 9-fluorenyl cation is significantly delocalized.