Zirkonium-katalysierte Oxidation von primären aromatischen Aminen zu Nitroverbindungen mittert-Butylhydroperoxid

Abstract

Zirconium‐catalysed Oxidation of Primary Aromatic Amines to Nitro Compounds Using tert‐Butylhydroperoxide A broad range of primary aromatic amines (1a–x) with electron donating and accepting substituents are oxidized in good to excellent yields to the nitro compounds 3a–x using tert‐butylhydroperoxide as the oxidant and Zr(OtBu)4 as the catalyst. The corresponding nitroso compounds 2m, 2n, 2s and 2u can be isolated in the conversion of electron‐rich anilines 1m, 1n, 1s and 1u. The aminopyridines 5a–d are also converted to the corresponding nitropyridines 6a–d, but in lower yields (41–47%).

Zirconium-Catalyzed Amine Oxidation: A Mechanistic Study

“…This stepwise oxygen transfer was investigated in a series of experiments on the oxidation of primary aromatic amines A (Scheme 1; x 0: R aryl). [2,3] The presence of hydroxylamines B as intermediates in the oxidation of aromatic amines was proved indirectly by the isolation of azoxy compounds, which were formed in a coupling reaction with the nitroso compounds C. Aromatic nitroso compounds C were isolated in up to 50 % yields when donor-substituted anilines were used as substrates. In kinetic competition experiments with 4-methoxyaniline, aniline, and 4-nitroaniline, the formation of 1,4-dinitrobenzene was observed from the very beginning, while 4-methoxy-1-nitrobenzene could be detected only after an induction period of % 30 min.…”

Zirconium-Catalyzed Oxidation of Primary Aliphatic Amines to Nitro Compounds withtert-Butyl Hydroperoxide

“…[1] The yields were generally very high in spite of the occurrence of two reaction intermediates (e.g. hydroxylamines and nitroso compounds) demonstrating the powerful oxygen transfer capability of the zirconium alkoxide/TBHP reagent.…”

“…The oxidation of primary amines A proceeds via a number of intermediates [18] (Scheme 1) and an efficient oxidant is required for rapid conversion to the target nitro compounds F. The occurrence of hydroxylamines B in the oxidation of aromatic amines was established indirectly by the isolation of azoxy compounds which were formed by coupling with nitroso compounds C. [1] The aromatic nitroso compounds were isolated in ca. 50% yield in the case of donator-substituted anilines.…”

“…50% yield in the case of donator-substituted anilines. [1] Further difficulties in the aliphatic series may arise from the tautomerization of the nitroso compounds C to the corresponding oximes D or dimerization to E. [18] Incomplete oxidation was sometimes observed in the reaction with MCPBA caused by the formation of nitroso dimers E. [14] Scheme 1 A variety of primary amines shown in Scheme 2 with different steric hindrance and functionalities have been selected to test the scope and limitation of the zirconium alkoxide/TBHP oxygenation procedure. The isolated yields of the oxidation of the amines 1Ϫ12 to the corresponding nitro compounds 13Ϫ24 are listed in Table 1 and refer to analytically pure samples.…”

“…[9] The oxidation of the corresponding primary amines which are easily prepared by substitution reac- [᭛] Part 9: Ref. [1] .…”