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.