Chemoselective nitrone formation

As anticipated from the chemistry of oxime and nitrone formation, we quickly fotmd that the amide formation was remarkably chemoselective. Carboxylic acids,... 

In all the above examples, the synthesis of nitronates (5) is rather chemose-lective. In any case, data on the formation of their structural isomers, viz, the corresponding nitrocyclopropanes (13), are lacking. However, the synthesis of five-membered nitronates (5) with the use of sulfur or selenium ylides is not chemoselective (see Scheme 3.16). 

---