Iodohexene Radical Cyclisation Endo

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NOTE: Important charges and non-bonding electrons are shown throughout the animation except during the transition state phase.

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Even though the six membered ring gives a stabilised radical as an intermediate, the formation of the five membered exo product is more favoured. The reaction proceeds via an abstraction of iodine by a trimethyltin radical. The chain can then twist into a position to cyclise. Not shown here is the abstraction of hydrogen from trimethyltinhydride by the methylcyclopentane radical to form the endo product.

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H. Fischer and L. Radom, Angew. Chemie Int. Ed., 2001, 40, 1340–1371.