Photoextrusion of SO2 from Arylmethyl Sulfones: Exploration of the Mechanism by Chemical Trapping, Chiral, and CIDNP Probes

Article abstract of DOI:10.1021/ja00318a037

The photochemistry of eight benzylic sulfones, all of which efficiently extrude sulfur dioxide, was studied by a variety of methods.Optically active sulfones (S)-(-)-8, (S)-(-)-11, (S)-(-)-12, (S)-(+)-13, and (R)-(+)-14 were employed to measure the extent of the "hidden" return of the initial photogenerated intermediates by the stereoequilibration of the chiral center.By comparison of the regioisomeric methyl sulfones 11 vs. 13 and 12 vs. 14, preferential C-S bond fragmentation on the naphthyl side was established for the singlet excited sulfones.Added nucleophilic and proton trapping agents had no effect on the course of the reaction, ruling out ionic intermediates.The three hydrocarbon products of photodesulfonation from the unsymmetrical sulfones 8-14 provided a measure of the cage effects, which were highly structure and multiplicity dependent.Rate constants for reaction, and fluorescence, as well as the energy transfer rates from benzophenone were determined.The reaction rate constant for singlet reactivity from the 1-naphthyl sulfones was about three times greater than that for the 2-naphthyl derivatives.CIDNP studies showed a strong product signal for the 1-naphthyl sulfones from desulfonation of a triplet caged radical pair.Naphthaldehyde formation, a very minor, triplet process, was also detected by the CIDNP study of sulfones 9-12.