Intramolecular radical cyclisations to pyridines

Intramolecular radical additions to the α-, β- and γ-carbons of a pyridine have each been shown to be facile processes. When a cis-alkene conjoins an ortho-iodoarene and a pyridine, radical cyclisation induced by homolysis of the carbon to iodine bond favours a 6-exo/endo-trig course. With a two carbon alkane conjoining the ortho-iodoarene and the pyridine, intermolecular hydrogen atom abstraction, 6-exo/endo-trig cyclisation and 5-exo-trig cyclisation modes compete. That the spirocyclic intermediates formed in the 5-exo-trig cyclisation rearrange with migration of the alkyl chain is noteworthy.