Via a Homolysis-Addition Pathway

Work in the group of Speckamp has shown that C-Cl bonds in a captodative position are weak enough to lead to radical chain cyclization reactions by chlorine atom transfer [28], Chlorine atom transfer from 34 to the catalyst, Cu Cl-bipyridine, leads to radical 35 which then undergoes 5-exo intramolecular addition to form the proline derivative 36 (Eq. 1). The captodative substitution is necessary for this radical process in the absence of an electron-withdrawing substituent, a cationic reaction leading to a piperidine occurs instead [29]. 

In a similar process, the a-chloro-a-thioacetamide 37 leads to the pyrrolizidines 38 and 39 upon chlorine atom-transfer cyclization initiated by catalytic ruthenium chloride (Eq. 2). The high efficiency of this method, which was applied to alkaloid synthesis, was attributed to the captodative effect [30], 

Phenylthio radicals add to the alkyne 40 to yield, after 1,5 intramolecular hydrogen transfer, the captodative a-alkoxyester 41, which cyclizes in good yield to the 2,3-disubstituted tetrahydrofurans 42 and 43 [31]. 

---