Alkyl iodides, intermolecular radical addition

The intermolecular radical addition of alkyl iodides to terminal alkynes has been used in cyclization cascades performed under radical chain conditions (Scheme 2.3). For example, Oshima and coworkers applied triethylborane as radical initiator to... 

The Naito group has also prepared pyrrolidines [23] on solid phase by a combination of intermolecular radical addition to alkene 43 (Scheme 10) followed by intramolecular oxime ether cyclization to yield 44. These reactions proceeded sluggishly with triethylborane at room temperature, while the analogous solution-phase process was kinetically much faster. Radical additions to the phenylsulfonyl oxime ether 45 were reported by Jeon et al. [24]. Yields were better with primary and secondary alkyl iodides, and the tandem cyclization sequence with iodide 46 to afford bicyclic 47 was also accomplished, albeit in modest yield. 

The second key to success in making sure that the alkyl radical behaves well is to use a reactive radical trap. In fact, this is a major limitation of intermolecular radical carbon-carbon bond-forming reactions for the trapping of alkyl radicals only electrophilic alkenes (attached to electron-withdrawing groups such as -CN, -CC Me, -COMe) will do. This is a limitation, but nonetheless, cyclohexyl iodide adds to all these alkenes with the yields shown and the rate of addition to most of these alkenes is 103 to 104 times that of addition to 1-hexene. 

Oxoesters are oxidized with Mn(OAc)3 to the corresponding radicals that can add intermolecularly or intramolecularly (eq Ib)" to generate alkyl radicals. In the presence of Cu(OAc)2 the latter are rapidly quenched and oxidized to give alkenes. Radical arylation with alkyl iodides can be induced with dibenzoyl peroxide the yield of the reaction can be improved using a catalytic amount of Cu(0Ac)2-H20, which minimizes hydrogen abstraction by the intermediate radical but introduces a competitive electron-transfer oxidation of the intermediate radical. The oxidative addition of disulfides to alkenes (Trost hydroxysulfenylation ) can be promoted by catalytic amounts ofCu(OAc)2. ... 

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