One-Pot Synthesis of Symmetrical Di- and Triarylamines Using Urea as the Source of the Amino Group

Abstract

A simple one-pot palladium-catalyzed reaction for the conversion of aryl halides to aryl amines using urea as an ammonia equivalent is reported. Arylation of urea in the presence of Pd₂dba₃, t-Bu₃P·HBF₄ and t-BuOK in dioxane gives di- and triarylamines in 65-95% yields.

palladium - arylations - amines - ammonia equivalents - urea

References and Notes

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Representative Procedure for Tri( m -tolyl)amine.
m-Bromotoluene (282 mg, 1.65 mmol), urea (31 mg, 0.51 mmol), Pd₂dba₃·CHCl₃ (31.5 mg, 0.03 mmol), t-Bu₃P·HBF₄ (25.2 mg, 0.087 mmol), t-BuOK (325 mg, 2.9 mmol), and anhydrous dioxane (6 mL) purged with argon were placed into an argon-filled reactor. The reaction was carried out with stirring at 100 °C under positive argon pressure. After the aryl halide was completely consumed (according to GC), the reaction mixture was cooled to r.t., diluted with EtOAc (30 mL), filtered through the short plug of Celite^® and evaporated on silica gel. The residue was chromatographed on silica gel (Merck 60, 40-63 µm), eluting with light PE, then EtOAc-light PE mixture 1:40 and 1:20 at the end to give 122 mg (85%) of the product as a white solid. Mp 66 °C (ref. 2: 64-65 °C). ¹H NMR (400 MHz, acetone-d ₆): δ = 7.14 (t, 3 H, 7.7 Hz), 6.77-6.87 (m, 9 H), 2.23 (s, 9 H). MS (EI, 70 eV): m/z (%) = 287 (100) [M⁺], 271 (2) [M - CH₃ - H⁺], 257 (4) [M⁺ - 2 CH₃], 180 (5) [C₁₃H₁₀N⁺].

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