Manganese(iii) acetate-mediated oxidative coupling of phenylhydrazines with benzene: a novel method for biaryl coupling

Abstract

The reaction of phenylhydrazines with benzene in the presence of manganese() acetate affords biaryls in good yields. The same reaction was carried out with similar oxidants, such as Co III , Ce IV and Pb IV ; among these oxidants Mn III acetate shows higher efficiency and selectivity.

Radical Arylation of Phenols, Phenyl Ethers, and Furans

“…Keywords: diazonium salts · biaryls · phenols · phenyl ethers · radical reactions phase-transfer variants, [17] the application of oxygen as reoxidant in tin-mediated radical biaryl syntheses, [18] and the application of arylhydrazines and Grignard reagents [19,20] as aryl radical precursors. Biaryl compounds can also be obtained by radical addition to a nonaromatic precursor and subsequent aromatization.…”

“…Although nonprotonated allylic amines are not suitable substrates due to extensive hydrogen abstraction from the allylic position, the protonated ammonium salts of these substrates react without difficulties. [41] The best results from the arylation of heterocycles were obtained with furan (18), [42] furfurylamine (19), and 2-methylfuran (24). All three substrates gave the desired biaryls in good yields and with high regioselectivity (Scheme 7).…”

Transition Metal‐Mediated Direct CH Arylation of Heteroarenes Involving Aryl Radicals

“…[75] More recently, manganese derivatives have emerged as powerful oxidants for free-radical generation from arylhydrazines. For instance, the group of Demir reported the reaction of phenylhydrazines with benzene with high yields, using 3 equivalents of manganese triacetate either preformed [76] or in situ generated from a KMnO 4 /CH 3 COOH mixture. [77] More recently, Heinrich et al extended the scope of this reaction to the synthesis of 2-aminobiphenyls from arylhydrazines and anilines, by exploiting the strong directing effect of the free unprotected amino group.…”

“…[76] Only the 2-substitued furan and thiophene were isolated, demonstrating the regioselectivity of the radical reaction. The scope of the reaction was then extended to electron-rich and electronpoor substituted phenylhydrazines in moderate to good yields (22-70%), usually higher for thiophene derivatives (Scheme 24).…”

Modern Developments in Aryl Radical Chemistry

“…Aryl boronic acids were used as aryl radical precursors in the presence of the strong oxidant manganese(III) acetate [146]. Earlier, the same group had reported on radical biaryl syntheses using manganese(III) acetate in combination with aryl hydrazines [147]. In a comparative arylation study on the use of aryl boronic acids, hydrazines, and aryl diazonium salts (PTGB protocol) for couplings with benzene, furan, or thiophene, the best yields were obtained when boronic acids were employed as radical sources.…”