Halogen, Sulfur, and Selenium Group Transfer Reactions

Halogen, Sulfur, and Selenium Group Transfer Reactions 

Other atoms and groups apart from hydrogen are susceptible to abstraction by free radicals. The most important from a synthetic point of view are bromine, iodine, sulfur, and selenium substituents. Group transfer reactions can occur inter- or intramolecularly. Indeed, we have already encountered one example in the addition of polyhalogenated methanes to alkenes. The chain is propagated by a bromine atom transfer. 

Cyclizations involving iodine atom transfers have been developed, and among the most effective examples are reactions involving the cyclization of 6-iodohexene derivatives. The 6-hexenyl radical generated by iodine atom abstraction rapidly cyclizes to a cyclopentylmethyl radical. The chain is propagated by iodine atom transfer. 

Various functionalized derivatives can be cyclized, including a-iodoesters, a-iodoketones, and a-iodomalonates. These substituents make the radical more electrophilic and reactive toward the alkene and also facilitate the iodine abstraction step. 

in Radicals in Organic Synthesis, P. Renaud and M. P. Sibi, eds., Wiley-VCH, Weinheim, 2001, Vol. 1, Chap. 1.5. 

Besides hydrogen, other atoms and groups are susceptible to abstraction by free radicals. The most important from a synthetic point of view are bromine, iodine, sulfur. 

Various functionalized derivatives can be cyclized, including a-iodoesters, a-iodoketones, 

The chain is propagated by abstraction of iodine by the cyclized vinyl radical intermediate. 

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SECTION 12.5. HALOGEN, SULFUR, AND SELENIUM GROUP TRANSFER REACTIONS... 

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