Intramolecular radical cyclisations to pyridines

Intramolecular radical additions to the alpha-, beta- and gamma -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. W ith a two carbon alkane conjoining the ortho-iodoarene and the pyridine, in termolecular hydrogen atom abstraction. 6-exo/endo-trig cyclisation and 5-e xo-trig cyclisation modes compete. That the spirocyclic intermediates forme d in the 5-exo-trig cyclisation rearrange with migration of the alkyl chain is noteworthy. (C) 2001 Elsevier Science Ltd. All rights reserved.