A dual biomimetic process for the selective aerobic oxidative coupling of primary amines using pyrogallol as a precatalyst. Isolation of the [5 + 2] cycloaddition redox intermediates

Abstract

Low-cost pyrogallol precatalyst undergoes an oxidative self-processing step for delivering the active organocatalyst in situ through a dual biomimetic process.

Oxidative coupling of primary amines to imines catalyzed by CoCl2·6H2O

“…In contrast, the reactions of the aliphatic amines were inefficient under the same conditions, such that only trace or no target imines were detected (Table 3, entries 1p-1s), most aliphatic imines are scarcely stable because they are easily isomerized into enamine tautomer which decomposed under air. [39] For most aromatic amines investigated here, the catalytic efficiency of CoCl 2 Á6H 2 O was comparable with or higher than the reported efficiencies with the other metal catalysts (such as Cu, [20] Ru, [15] Au, [17] V [23] ) and Co complexes. [34] Interestingly, for the heteroaromatic methanamine, the catalytic data mentioned above have indicated a higher efficiency compared with the previously reported catalysts.…”

Carbon Chain Rupture: Base-Induced Radical C–C Bond Cleavage of Alkylbenzimidazoles

“…We surprisingly found that non-negligible amount of benzoic acid (22%, 7) was also formed when 4-phenylbutyl benzimidazole (5) was subjected to the reaction and corresponding carboxylic acid 6 was isolated in 40% yield, while benzimidazole 2a was obtained in 71% yield. However, a trace amount of benzoic acid was detected when 4-phenylbutanoic acid 6 (or butylbenzene, 8) and 2-methylbenzimidazole (1j) were mixed under the standard conditions.…”

“…The data match with literature. 11 2-Heptyl-1-methyl-1H-benzo[d]imidazole (1p). Following general procedure, o-phenylenediamine (216.0 mg, 2.0 mmol) and octanoic acid (288.4 mg, 2.0 mmol) were selected as the substrates.…”

“…The residue was purified by flash column chromatography (petroleum ether/AcOEt = 80:20) to afford 3l (380.0 mg, 81%) as light-yellow oil. (5). Following general procedure, o-phenylenediamine (324.0 mg, 3.0 mmol) and 5phenylpentanoic acid (534.6 mg, 3.0 mmol) were selected as the substrates.…”

“…4 The radical generated under reductive conditions also played significant role in synthesis; reactions such as Birch reduction, Grignard reaction and Meerwein-Ponndorf-Verley reduction were proved to be radical processes. 5 More recently, the coupling of aryl halides with unactivated arenes using t BuOK and Ncontaining ligands have been simultaneously developed by Shi, Hayashi and Lei groups. 6 The C-C rupture reactions with t BuOK under transition-metal-free conditions were also developed.…”