Silyl Cyanopalladate-Catalyzed Friedel-Crafts-Type Cyclization Affording 3-Aryloxindole Derivatives

Hamdiye Ece, Yuji Tange, Taiga Yurino*, Takeshi Ohkuma*

*Faculty of Engineering, Hokkaido University, Kita 13, Nishi 8, Sapporo, Hokkaido 060-8628, Japan, Email: tyurinoeng.hokudai.ac.jp, ohkumaeng.hokudai.ac.jp

H. Ece, Y. Tange, T. Yurino, T. Ohkuma, Synlett, 2021, 32, 935-939.

DOI: 10.1055/a-1373-7017

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Abstract

Trimethylsilyl tricyanopalladate complex generated in situ from trimethylsilyl cyanide and Pd(OAc)₂ catalyzes the conversion of various diethyl phosphates derived from N-arylmandelamides into oxindoles in excellent yields. With a N,N-dibenzylamide as substrate, a benzo-fused δ-lactam was obtained.

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General Procedure

A 20 mL Schlenck flask was used as a reaction vessel, and the reaction was performed under argon atmosphere using normal Schlenk techniques. A solution of diethyl 2-[methyl(phenyl)amino]-2-oxo-1-phenylethyl phosphate (1a: 130 mg, 0.35 mmol) and Pd(OAc)₂ (1.6 mg, 7.0 μmol) in MeNO₂ (2.0 mL) was stirred for 15 min at 60 °C. To the solution, TMSCN (71 mg, 0.72 mmol) was added, and was stirred at 60°C for 10 h until the reaction was complete [TLC, hexane-EtOAc (4:1)]. The reaction was quenched with saturated aq NaHCO₃. The aqueous layer was extracted with EtOAc (3 × 10 mL). The collected organic layers were washed with brine, and then dried over Na₂SO₄. After Na₂SO₄ was filtered off, the residue was concentrated in vacuo. The yield of the product (>99%) was determined from the ¹H NMR spectrum of the crude product, with pyrazine as an internal standard. The product was isolated by preparative TLC (hexane-EtOAc, 4:1) as a white solid.

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Key Words

Lewis acid catalysis, Friedel-Crafts reaction, cyclization, oxindoles, S_N1 reaction

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ID: J72-Y2021