Abstract
The radical reaction of benzenethiol with alkynes 1a-o carried out at 154 °C affords a mixture of thiol/alkyne adduct 3 and benzothiophene 5, deriving from vinyl radical intermediates 2 through hydrogen abstraction and 5-(π-endo)orthocyclization onto the adjacent thiophenyl ring, respectively. This latter reaction occurs through the reversible formation of cyclohexadienyl radical intermediates 4 which can evolve to 5 to an extent largely depending on the reaction conditions employed. The 5-ortho cyclization is governed both by stereoelectronic factors, which favor the cyclization of p-centered, linear α-arylvinyl radicals 2a-f, and polar factors, which favor the cyclization of α-EWG substituted vinyl radicals 2c,n,o.
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