Direct Synthesis of Diphenylamines from Phenols and Ammonium Formate Catalyzed by Palladium

Abstract

Arylamines are commerciallya nd synthetically useful compounds with aw ide variety of applications.T heir preparation has been traditionally achieved using metal-catalyzedC ÀN coupling reactions with aryl halides. In this work, 17 different diarylamines are prepared from phenolsb yu sing ammonium formate as the aminatingr eagent. Phenolicc ompounds are more desirable feedstocks, owing to their availability from lignin, making them valuable biorenewable alternatives to aryl halides. Ammonium formate is found to be aconvenient surrogate for ammonia and au seful aminating reagent for phenols. Diarylamine products are obtained in good to excellent yields while only water and CO 2 are generated as byproducts of the transformation.Arylamines are valuable commodity chemicals, owing to their broad application as antioxidizers and as synthetically relevant buildingblocks. Diphenylamine (DPA) is primarily used as astabilizer for nitrocellulose explosives [1] and the detection of oxidizers, [2] whereas C-alkylated diphenylamines are widely used as antioxidants for the preservation of fruits, [3] oils, [4] and polymers. [5] Further uses of arylamines include being ap recursor for the synthesis of (azo-)dyes, [6] and nonsteroidal anti-inflammatoryd rugs. [7] Additionally,t riphenylamines are important for the preparation of optoelectronic materials. [8] For at horough review on the use of these compounds, please see the reference articles by Drzyzga [9] and Layer. [10] Arylamines are commonly prepared from amine precursors through metal-catalyzedC ÀNc oupling reactions. Methods for the formation of these compounds include the Stille, [11] Chan-Evans-Lam, [12] Ullmann, [13] and Buchwald-Hartwig [14] couplings. In addition, other methods, including P III /P V =Oc atalysis, [15] iodine, [16] sulfonium triflates, [17] various nanoparticle catalysts, [18] and Pd/C catalysis for the formationo fa rylamines from aliphatic substrates, [19] have also been reported. Similard evelopments for the formation of diaryl ethers have also been reported. [20] Phenol can be obtainedf rom naturals ources, as one of the basic units of lignin, making it an attractive biorenewable feed-

Sustainable access to renewable N-containing chemicals from reductive amination of biomass-derived platform compounds

“…Similar to N-cyclohexyl aniline, diphenylamine was accessible from the reductive amination of lignin-derived phenolic model monomers as delineated in Scheme 13. The first and unique example for the synthesis of diphenylamine from reductive amination of phenol was done by Li et al [155] using Pd/C and ammonium formate as catalyst and nitrogen/hydrogen sources, respectively. Up to 98% yield of diphenylamine was achieved under argon atmosphere at 160 °C in 24 h. Moreover, the authors reported 17 different diarylamines synthesized from the reductive amination of phenols with moderate to excellent yields (25-98%) using the described catalytic system [155].…”

“…The first and unique example for the synthesis of diphenylamine from reductive amination of phenol was done by Li et al [155] using Pd/C and ammonium formate as catalyst and nitrogen/hydrogen sources, respectively. Up to 98% yield of diphenylamine was achieved under argon atmosphere at 160 °C in 24 h. Moreover, the authors reported 17 different diarylamines synthesized from the reductive amination of phenols with moderate to excellent yields (25-98%) using the described catalytic system [155]. Furthermore, the authors clearly elaborated the possible reaction mechanism taking the reductive amination of phenol with ammonium formate as an example [155].…”

Symmetrical Tertiary Amines: Applications and Synthetic Approaches

“…In 2019 a similar protocol was reported by Li and co-authors. [359] They used cyclohexenone to insert the third phenyl ring in the Ph 2 NH structure in the presence of Pd on carbon (Scheme 139). Scheme 139.…”

Dearomatization–Rearomatization Strategy for Palladium-Catalyzed C–N Cross-Coupling Reactions

“…In 2019, our group used the same strategy to directly synthesize diarylamines from phenols and ammonium formate (Scheme 5). 15 Various diarylamine products were obtained in good to excellent yields except for severely sterically hindered substrates bearing multiple ortho substituents. Although large amounts of phenols are required to increase the yield, the phenols could be recovered after the reaction.…”