Photoreduction of Cyclic α‐Fluoroketones

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Abstract
Irradiation of the α‐fluoroketones 1a and 6a in i‐PrOH selectively affords the parent ketone 1b and 6b, respectively. It is concluded that in this solvent heterolytic C‐F bond cleavage of the anion radical‐formed by electron transfer to the excited fluoroketone‐is a faster process than the subsequent protonation by the cation radical of the solvent. In cyclohexane 1b and 6b are only formed in minor amounts, the fluorinated RH‐reduction product 4 now being the major product from 1a. In non‐reducing solvents as t‐BuOH or benzene 2‐fluorocyclohexanone (1a) exhibits a similar behavior as cyclohexanone (1b) on excitation. The quantum yields for α‐cleavage are alike for both compounds, but oxetane formation with 2‐methylpropene as olefinic component occurs much more readily with 1a than with 1b.