Synlett 2009(14): 2236-2241  
DOI: 10.1055/s-0029-1217805
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

Thieme Chemistry Journal Awardees - Where Are They Now? Bifunctional Silver Acetate Catalyzed Asymmetric Mannich-Type Reactions

Qing-An Chen, Wei Zeng, Da-Wei Wang, Yong-Gui Zhou*
State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, 457 Zhongshan Road, Dalian 116023, P. R. of China
Fax: +86(411)84379220; e-Mail: ygzhou@dicp.ac.cn;
Further Information

Publication History

Received 5 June 2009
Publication Date:
07 August 2009 (online)

Abstract

Efficient bifunctional silver acetate catalyzed three asymmetric Mannich-type reactions with high reactivity, up to >95:5 diastereoselectivities and moderate to excellent enantioselectivities (up to 97% ee). External base is not required in this bifunctional catalytic procedure, in which acetate promotes the deprotonation.

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General Procedure for the Silver Acetate Catalyzed Mannich Reactions (Table 4, entry 1): Ligand (0.0075 mmol) and AgOAc (1.2 mg, 0.007 mmol) were placed in a dried Schlenk tube under a nitrogen atmosphere and Et2O (1.0 mL) was added. The mixture was stirred at room temperature for about 0.5 h. After cooling to the indicated temperature, α,α-dicyanoolefin (0.23 mmol) was added as a solution in Et2O (1.0 mL) followed by addition of aldimine (0.276 mmol). Progress of the Ag-catalyzed Mannich reaction was typically monitored by TLC analysis. Upon consumption of the limiting reagent, the reaction was isolated by a short column of silica gel chromatography directly. The ratio (syn/anti) was determined by NMR spectroscopic analysis of the crude product. The crude adducts were purified by column chromatography on silica gel.

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Selected physical and spectral data for 7a: white solid, 64% ee, [α]D ²³ -82.9 (c 1.03, CHCl3); R f 0.55 (PE-EtOAc, 5:1); HPLC (Chiralpak AD-H column; i-PrOH-hexane, 95:5; 0.8 mL/min; 254 nm; 30 ˚C): t R(minor) = 8.2 min, t R(major) = 13.6 min; ¹H NMR (400 MHz, CDCl3): δ = 8.06 (d, J = 7.9 Hz, 1 H), 7.51 (t, J = 7.4 Hz, 1 H), 7.41-7.24 (m, 7 H), 4.94-4.92 (m, 1 H), 4.53 (t, J = 10.4 Hz, 1 H), 3.72-3.68 (m, 1 H), 2.89-2.85 (m, 1 H), 2.70-2.66 (m, 1 H), 1.93-1.89 (m, 1 H), 1.51-1.47 (m, 1 H), 1.42 (s, 9 H); ¹³C NMR (100 MHz, CDCl3): δ = 175.1, 154.7, 140.0, 138.9, 133.5, 129.8, 129.4, 128.7, 128.6, 127.0, 126.9, 114.2, 113.6, 82.1, 80.2, 57.5, 49.1, 28.3, 25.9, 25.2.