Thermal decomposition of tert-butyl ortho-(phenylsulfanyl)- and ortho-(phenylsulfonyl)phenyliminoxyperacetates: The reactivity of thio-substituted iminyl radicals

Some ortho-(phenylsulfanyl)- and ortho-(phenylsulfonyl)-substituted phenyliminyl radicals have been generated by thermal decomposition of suitable tert-butyl iminoxyperacetates. The sulfanyl-substituted iminyls showed no tendency to give either 1,7- or 1,6-ring closure onto the S-phenyl ring. They gave instead 1,5-cyclisation onto the sulfur atom with release of a phenyl radical and formation of benzoisothiazoles. This seems to be the first example of S(H)i reaction of a nitrogen-centred radical at a sulfide moiety. On the other hand, the sulfonyl-substituted iminyl underwent 1,6-cyclisation to a small extent, furnishing a phenanthridine through an unprecedented 1,5-aryl radical migration from sulfur to nitrogen followed by loss of sulfur dioxide and ring closure of an aryl radical.