Regioselectivity of ring closure of the 2-azonia-2,2,5-trimethyl-5-hexenyl radical

The 2-azonia-2,2,5-trimethyl-5-hexenyl radical 9, derived from treatment of 1-iodo-2,2,5-trimethyl-2-azonia-5-hexenyl iodide 12 with tributyltin hydride, is found to give an 8:3:1 mixture of the isomeric 5-exo, 6-endo and acyclic ammonium salts. A rationale for the observed regioselectivity is proposed, and a comparison is made with the behaviour of the corresponding all-carbon radical.