Oxime ethers nucleophilic radical addition

The C=N bond of simple imines possesses modest reactivity toward intermolecular radical additions, so such acceptors have rarely been exploited. To enhance their reactivity toward nucleophilic radicals, electron-withdrawing groups at the imine carbon have been effective, as demonstrated by Bertrand in radical additions to a-iminoesters prepared from chiral amines [25]. Also, more reactive oxime ethers have been exploited extensively for radical addition, mainly through the longstanding efforts of Naito [26]. In most cases, stereocontrol has been imparted through the substituents on the imino carbon chiral O-substituents on oximes for stereocontrol were ineffective, presumably due to poor rotamer control [27, 28]. 

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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