Direct observation of a 1,4-hydrogen shift in vinyl radicals derived from the reaction of alkynes with thiyl radicals

Abstract

E.s.r. experiments demonstrate that in vinyl radicals generated from thiyl radicals and alkynes, intermolecular abstraction of a thiol hydrogen (k≈ 10⁷ dm³ mol^–1 s^–1) is in competition with 1,n-hydrogen shifts. A rapid 1,4-shift (k≈ 10⁵ s^–1) is shown to occur in cases where the resulting radical is stabilized by the presence of α-sulphur and α-carboxy substituents, whereas in other examples a 1,5-shift predominates.