Radical cyclization, and

Organic halides play a fundamental role in organic chemistry. These compounds are important precursors for carbocations, carbanions, radicals, and carbenes and thus serve as an important platform for organic functional group transformations. Many classical reactions involve the reactions of organic halides. Examples of these reactions include the nucleophilic substitution reactions, elimination reactions, Grignard-type reactions, various transition-metal catalyzed coupling reactions, carbene-related cyclopropanations reactions, and radical cyclization reactions. All these reactions can be carried out in aqueous media. 

Scheme 20.20 Tandem enyne-allene and radical cyclizations.

Fig. 6. Polymer-supported IBX (resin 5) can be activated and recycled with monoperoxy sulfonic acid (Caro s acid). The polymer reagent is capable of alcohol oxidations, dehydrogenations, and radical cyclization reactions.

Natural products containing six-membered rings are ubiquitous, therefore the following set of target molecules are limited to those containing eight-membered rings that would be accessible via [4+4] cycloadditions. Notably, 1,5-cyclo-octadienes 88 can be converted to bicyclo[3.3.0]octanes 201 transannular electrophilic [124] and radical cyclization (Sch. 44) [125]. 

A nice extension of this chemistry to sequential anionic/radical/anionic sequence was also provided [5, 9]. Normally after acyl addition and radical cyclization onto a C = C bond, the newly formed carbon radical is reduced to an organosamarium intermediate which is subsequently protonated. However, as depicted in Scheme 5, this organosamarium may be trapped in the presence of a ketone substrate, thus terminating this three-step process. In another demonstration of how such anions may be further exploited, substrates possessing vinyl ethers as the radical acceptor were found to under-... 

D. P. Curran, Radical Addition Reactions, and Radical Cyclization Reactions and Sequential Radical Reactions. In Comprehensive Organic Synthesis, B. M. Trost, I. Fleming, Eds. Pergamon Elmsford, NY, 1991 Vol. 4, Chapters 4.1 and 4.2. 

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