Enantioselective Rh-Catalyzed Addition of Arylboronic Acids to N-Tosylarylimines

Abstract

A highly enantioselective rhodium-catalyzed addition of arylboronic acids to N-tosylarylimines is described, using chiral ­binaphtholic phosphite and phosphoramidite ligands. The best ee values (76-99%), associated with moderate to good chemical yields, were obtained with binaphtholic phosphoramidite ligands containing a bulky chiral amine.

arylations - arylboronic acids - asymmetric catalysis - imines - rhodium

References and Notes

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General Procedure for the Arylation of N -Tosylaryl-imines: In a flame-dried Schlenk tube flushed with nitrogen, Rh(acac)(C₂H₄)₂ (1.2 mg, 4.65 µmol, 3 mol%) and the ligand (9.30 µmol, 6 mol%) were dissolved in anhyd dioxane (0.75 mL). After stirring for 30 min at r.t., LiF (1.5 mmol) and the substrate (0.15 mmol) were added followed by the appropriate arylboronic acid (0.75 mmol). The resulting mixture was stirred at 50 °C for 24 h, quenched with H₂O (3 mL) and extracted with CH₂Cl₂ (3 mL). The organic phase was dried over Na₂SO₄ and the solvent was evaporated under vacuum. The residue was purified by flash chromatography on silica gel (n-hexane-EtOAc, 7:3) affording the N-tosyl-diarylmethylamine as a white solid.

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