Kolbe reactions radical cyclizations

The radical produced from the oxidative decarboxylation may also be trapped intramolecularly to form five- and six-membered rings (Scheme 17). The Kolbe protocol avoids the use of the toxic organ-otin reagents that are commonly used in the formation of radicals. Moreover, when alkyltin hydride reagents are used, a C—H bond is formed. The Kolbe reaction protocol, on the other hand, allows the radical formed after cyclization to be captured by a different radical in a coelectrolysis experiment, rather than being reduced. This tandem sequence of events has been exploited in the construction of prostaglandin precursor (70) [37-41]. Here, the cyclized... 

The Kolbe electrolysis has also been used to initiate tandem radical cyclization reactions [21]. Recently, Matzeit and Schafer reported that these reactions could be used to construct angularly fused tricyclic ring skeletons (Scheme 8) [22]. The reaction led to the formation of three new C-C bonds. In addition to the desired tricyclic product, the reaction formed a pair of products having the... 

Some A -enecarboxylic acids undergo a rapid intramolecular cyclization reaction of the 5-exo-trig type prior to the radical coupling step. Substituted tetrahydro-furans [95] and pyrrolidines [96] can be prepared by this Kolbe route. It is preferable to protect the amine function in the pyrrolidine synthesis by N-formy ation in... 

The addition of alkyl radicals to less reactive alkenes becomes more efficient if the addition is conducted intramolecularly. The Kolbe electrolysis of A 7- and A -unsaturated carboxylates produces five-and six-membered rings in a 5- or 6-cj o-rng-cyclization. ° Such a cyclization was first observed by Weedon and later studied in more detail." By intramolecular addition of appropriate precursors, 3-substituted tetrahydrofurans (Scheme 10 40, 41%), pyrrolidines (41, 53%), and cyclopentanes (42, 74%), and (43, 75%) are obtained. In the reactions leading to cyclopentanes the extent of cyclization... 

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