Deoxygenation of nitro and nitrosoaromatics by photolysis with t‐BuHgl/Kl. Regiochemistry of tert‐Butyl radical addition to nitrosoaromatics [1]

Photolysis of nitroaromatics in the presence of t‐BuHgI/KI in Me₂SO or DMF leads to products formed by t‐Bu^• addition to the nitroso compounds. Similar products are formed in the dark in the presence of K₂S₂O₈. Nitroso or nitrobenzene is converted into N,O‐di‐tert‐butylphenylhydroxylamine by a process involving N‐tert‐butylphenylhydroxylamine as an intermediate. In the presence of PTSA and KI, N‐tert‐butylphenylhydroxylamine predominates in Me₂SO, but in DMF, the phenylhydroxylamine is reduced to N‐tert‐butylaniline. In a similar fashion, o‐nitrosotoluene is converted into o‐MeC₆H₄N(Bu‐t)OBu‐t, o‐MeC₆H₄N(Bu‐t)OH, and o‐MeC₆H₄NHBu‐t. p‐Nitroso‐N,N‐dimethylaniline forms the N,O‐di‐tert‐butylated derivative in the absence of acid but in the presence of PTSA/KI yields p‐Me₂NC₆H₄NHBu‐t. Excellent yields of the N,O‐di‐tert‐butylated arylhydroxylamines are formed in DMF from the nitroaromatics with para Me₂N, OH, I, Br, Cl, and ortho Ph or PhNH substituents. Nitrobenzenes with p‐CHO, p‐PhCO, or p‐CN substituents are deoxygenated to the nitroso compounds which react with t‐Bu^• to form the tert‐butoxyamino radicals (ArṄOBu‐t). In Me₂SO, the amino radicals react to form ArN(HgI)OBu‐t compounds which condense with the nitroso compounds to yield the azoxy compounds. With the p‐CN substituent, the azoxy compound is subsequently deoxygenated and tert‐butylated to yield p‐NCC₆H₄N(Bu‐t)NHC₆H₄CN‐p. In the presence of PTSA/KI, the amino radicals are reduced to p‐Y‐ArNHOBu‐t (Y = PhCO, CN). The compounds Y‐ArN(Bu‐t)OBu‐t undergo photochemical degradation to yield Y‐ArNHBu‐t with Y = p‐PhCO or p‐CN in a reaction that is inhibited by I⁻. With PTSA/H₂O/KI in Me₂SO, p‐Me₂NC₆H₄N(t‐Bu)OBu‐t is converted into 4‐(N‐tert‐butylimino)‐2,5‐cyclohexadien‐1‐one, p‐Me₂NC₆H₄NHBu‐t, and p‐tert‐butylamino‐m‐tert‐butoxy‐N,N‐dimethylaniline. o‐MeC₆H₄N(Bu‐t)OH reacts with PTSA/KI to form o‐MeC₆H₄N(Bu‐t)H in DMF or a mixture of the aniline and 4‐(N‐tert‐butylimino)‐3‐methyl‐2,5‐cyclohexadien‐1‐one in Me₂SO. In the absence of KI, only the cyclohexadienone is formed in Me₂SO.