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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 60C 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.


Key Words

Lewis acid catalysis, Friedel-Crafts reaction, cyclization, oxindoles, SN1 reaction


ID: J72-Y2021