Cu(I)‐Catalyzed <i>N</i> ‐Mono‐ and <i>N,O</i> ‐Diallylation of Nitroaromatic Compounds Using Allylic Borane‐Amine Adducts

Amine adducts of triallylic boranes reductively allylate nitroaromatic compounds in the presence of 1–5 mol% of phosphine‐ or NHC‐copper(I) complexes, yielding N,O ‐diallylic hydroxylamines with high selectivity. The reaction rate is strongly dependent on the amine component of the adducts, with the DABCO adduct proving the most reactive. The effects of solvent, ligands, and temperature on yield and selectivity are investigated. Even sterically hindered nitroaromatics, such as 2,6‐dimethylnitrobenzene underwent selective monoallylation providing N ‐allyl‐ and N ‐(methallyl)hydroxylamines. The reaction's broad scope is demonstrated with 22 different nitroaromatics bearing both electron‐donating and electron‐withdrawing substituents and it is successfully scaled up to 6 grams. Allylation of 2‐allylnitrobenzene for mechanistic studies revealed the formation of indoline derivatives, indicating the involvement in the transformation of N ‐centered radicals. This is further supported by the isolation of traces of bicyclic compounds derived from radical cyclizations during the reaction with nitrobenzene.