Cyclization, radicals with nitrile oxides

Similarly, ethyl nitroacetate afforded, with 1,4-naphto-quinones, fair yields of condensed isoxazoline derivatives as a result of dehydration followed by elimination or dehydrogenation [80]. Later, more examples of condensations of ethyl nitroacetate and alkenes in the same reaction conditions have been reported to compete with oxidation [81]. The intramolecular version, using allyl nitroacetate 16 in the presence of Cu(II) and Mn(III), gives mainly the bicyclic isoxazoline 17 as the condensation product, predominant over monoelectronic oxidation 18 (Scheme 8.6). Noticeably, the intramolecular cyclization occurs with Cu (II) or Co(II) instead of Mn(III) acetate. As expected, secondary nitro compounds undergo only radical reactions. Condensations are reported to occur via intermediate nitrile... 

We have found that oxidative cyclizations can be terminated by addition to nitriles to give iminyl radicals, such as 14 that is reduced to imine 15, which is hydrolyzed to ketone 16 on workup (Scheme 4) [21]. Ryu and Alper reported that radicals, such as 18 formed in the oxidative cydization of 17, add to carbon monoxide to give acyl radicals such as 19, which are oxidized by Mn(III) to acyl cations that react with water leading to carboxylic acids on workup as in formation of 20 (Scheme 5) [22]. 

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