Direct measurements of the rates of 1,3- and 1,5-sigmatropic hydrogen shifts in the photo-Fries rearrangements of phenyl acetate

Article abstract of DOI:10.1016/0009-2614(94)80006-5

The rate constants for the 1,3- and 1,5-sigmatropic hydrogen shifts of the photo-Fries rearranged intermediates of phenyl acetate produced by laser flash photolysis at 266 nm were directly measured in several solvents.The rate constants for the 1,3-hydrogen shift (3.6 s^-1) was faster than for the 1,5-shift (6.5E-2 s^-1) in the ground state in methylcyclohexane at 293 K, contrary to the expectation by the Woodward-Hoffmann rule.In protic solvents, ethanol and methanol, a remarkable increase in the rate constants (ca. 1E5 s^-1) was observed.A tentative mechanism including the role of the non-bonding electrons of the intermediates is discussed.