Nitroxide radicals. Part 21. Spontaneous decomposition of N-aryl 1- and 2-naphthyl nitroxides

Rhodium‐Catalyzed Direct Amination of Arenes with Nitrosobenzenes: A New Route to Diarylamines

“…Species C is protonated to produce the hydroxylamine 4 and the Rh III catalyst. As previously reported,13 nitroxide D is generated from 4 and oxygen. This transformation proceeds more quickly in the presence of the Rh III complex 16.…”

“…[13] The structure of 3 was confirmed by X-ray crystallography ( Figure 1). Control experiments revealed that the Rh III complex is essential and that the addition of water did not affect the yield (entries [13][14]. In contrast, the addition of an acid gave a dramatic increase in the reaction yield (entries 7-9) and 1-AdCO 2 H proved to be particularly effective (entry 9).…”

“…meta-Substituted derivatives underwent this amination reaction only at the sterically more accessible CÀH bond (11)(12)(13). 2-Arylpyridines bearing both electron-donating and electron-withdrawing groups were viable substrates for this amination reaction, giving the corresponding diarylamine products (5-14) in good to excellent yields.…”

“…2‐Phenylpyridine ( 1 a ) and methyl 4‐nitrosobenzoate ( 2 a ) were chosen as the model substrates (Table 1). When 1 a was treated with [RhCp*(CH 3 CN) 3 ](SbF 6 ) 2 (2.5 mol %, Cp*=pentamethylcyclopentadienyl and 2 a in PhCl, at 100 °C for 10 h under air, the desired diarylamine, 3 , was obtained in 35 % yield, possibly resulting from cleavage of N , N ‐diaryl hydroxylamine 4 (entry 3) 13. The structure of 3 was confirmed by X‐ray crystallography (Figure 1).…”

Rhodium‐Catalyzed Mild C7‐Amination of Indolines with Nitrosobenzenes

“…Subsequently, Protonation of species C produces a hydroxylamine D and regenerates the Cp*Rh(III) catalyst. Under the action of molecular oxygen, hydroxylamine D deliveres to N−O radicals E , which undergoes dimerization and rapid fragmentations to give aminyl radicals F . Finally, proton extraction from the solvent gives the aminated product 3 aa .…”