Radical Intermediates in the Photoreaction between Disulfides and Acylsilanes

Article abstract of DOI:10.1021/jo00198a008

Photolysis of cylopropane solutions of a number of disulfides RSSR (R = Me, n-Bu, CF3) in the presence of acylsilanes R'C(O)SiMe3 led to radicals of general structure R'C<*>(OSiMe3)SR which have been detected by EPR spectroscopy.The structure of the observed paramagnetic species has been ascertained by producing PhC<*>(OSiMe3)SMe via an alternative route, i.e., by reacting Me3Si<*> radicals with the thio ester PhC(O)SMe.The lifetime of these radicals varies considerably with the bulkiness of the substituents in the neighborhood of the radical center.The decay rates as a funct ion of temperature, together with the corresponding activation parameters, have been determined for the hindered t-BuC<*>(OSiMe3)SCF3 radical; it is suggested that the decay process involves an equilibrium with a dimeric species.A number of possible reaction sequences leading to these radicals have been examined, although the actual mechanism is as yet unclear.