Alkoxycarbonyl Radical Intermediates

However, if the substituents on the methano or imino bridges contain at least one substituent such as a phenyl or alkoxycarbonyl group stabilizing radical intermediates, facile thermal rearrangements from [5,6]-bridged to the thermodynamically more stable [6,6] -bridged isomers can take place, allowing in some cases for a complete conversion [129-131]. The photochemical extrusion of N2 leads preferably to [6,6]-adducts [132]. The exclusive formation of cluster open... 

Miyabe et al. developed a tandem addition/cycUzation reaction featuring an unprecedented addition of alkoxycarbonyl-stabihzed radicals on oxime ethers [117], and leading to the diastereoselective formation of /1-amino-y-lactone derivatives [118,119]. The reaction proceeds smoothly in the absence of toxic tin hydride and heavy metals via a route involving a triethylborane-mediated iodine atom-transfer process (Scheme 37). Decisive points for the success of this reaction are (1) the differentiation of the two electrophilic radical acceptors (the acrylate and the aldoxime ether moieties) towards the nucleophilic alkyl radical and (2) the high reactivity of triethylborane as a trapping reagent toward a key intermediate aminyl radical 125. The presence of the bulky substituent R proved to be important not only for the... 

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