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Synlett 2005(11): 1675-1678  
DOI: 10.1055/s-2005-871546
LETTER
© Georg Thieme Verlag Stuttgart · New York

Seleno-Imine: A New Class of Versatile, Modular N,Se Ligands for ­Asymmetric Palladium-Catalyzed Allylic Alkylation

Antonio L. Braga*, Márcio W. Paixão, Graciane Marin
Departamento de Química, Universidade Federal de Santa Maria, 97105-900, Santa Maria, RS, Brazil
Fax: +55(55)32208998; e-Mail: albraga@quimica.ufsm.br;
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Publication History

Received 28 April 2005
Publication Date:
14 June 2005 (online)

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Abstract

The palladium-catalyzed asymmetric allylic alkylation of 1,3-diphenyl-2-propenyl acetate with dimethyl malonate in the presence of chiral seleno-imine ligands derived from an inexpensive and easily available chiral pool was investigated. Excellent yield and enantioselectivity (up to 97% ee) was achieved when ligand 4a was used.

Key words

seleno-imines - allylic alkylations - palladium-catalyzed

11

General Procedure for the Synthesis of Seleno-Imine Ligands 4a-i: An equimolar mixture of 3 (1 mmol) and the requisite aromatic aldehyde (1 mmol) with MgSO4 (0.54 g/mmol) was stirred in EtOH (2.5 mL/mmol) for 24 h. Filtration and concentration in vacuo gave ligands 4a-i as oils, which were unstable to chromatography, the compounds were obtained as practically pure materials.
4a: Yield: 90%; [α]D 20 +54 (c 0.6, CH2Cl2). 1H NMR (CDCl3, 400 MHz): δ = 8.14 (s, 1 H), 7.76-7.71 (m, 2 H), 7.37-7.04 (m, 8 H), 3.69 (dd, 2 H, J = 12, J = 19), 2.97-2.76 (m, 3 H), 1.92-1.90 (m, 1 H), 0.88 (d, 6 H, J = 5.8). 13C NMR (CDCl3, 100 MHz): δ = 160.36, 139.55, 136.18, 130.44, 129.66, 128.93, 128.88, 128.50, 128.25, 77.93, 33.17, 28.98, 28.32, 22.63, 19.70. HRMS-ESI: m/z calcd for C19H23NSe + H+: 346.1073; found: 346.1063.
4b: Yield: 65%; [α]D 20 -29 (c 0.276, CH2Cl2). 1H NMR (CDCl3, 400 MHz): δ = 7.88 (s, 1 H), 7.67-7.64 (m, 2 H), 7.39-6.93 (m, 13 H), 3.75 (dd, 2 H, J = 12, J = 21), 3.46-3.44 (m, 1 H), 3.04-2.80 (m, 4 H). 13C NMR (CDCl3, 100 MHz): δ = 160.81, 139.41, 138.55, 135.84, 130.50, 129.60, 129.22, 128.80, 128.59, 128.42, 128.31, 126.46, 126.03, 76.68, 42.95, 30.99, 27.50. HRMS-ESI: m/z calcd for C23H23NSe + H+: 394.1074; found: 394.1084.
4c: Yield: 72%; [α]D 20 +21 (c 1.13, CH2Cl2). 1H NMR (CDCl3, 400 MHz): δ = 8.16 (s, 1 H), 7.76-7.74 (m, 2 H), 7.42-7.40 (m, 3 H), 7.28-7.17 (m, 5 H), 3.77-3.73 (m, 2 H), 3.31-3.29 (m, 1 H), 2.77-2.61 (m, 2 H), 1.69-1.63 (m, 1 H), 1.48-1.39 (m, 2 H), 0.89-0.81 (m, 6 H). 13C NMR (CDCl3, 100 MHz): δ = 160.40, 139.57, 136.05, 130.60, 129.72, 128.57, 128.40, 128.25, 126.57, 69.91, 45.35, 31.20, 27.70, 24.67, 23.55, 21.38. HRMS-ESI: m/z calcd for C20H25NSe + H+: 360.1230; found: 360.1224.
4d: Yield: 70%; [α]D 20 +13 (c 1.08, CH2Cl2). 1H NMR (CDCl3, 400 MHz): δ = 8.16 (s, 1 H), 7.77-7.75 (m, 2 H), 7.41-7.39 (m, 3 H), 7.26-7.17 (m, 5 H), 3.74-3.66 (m, 2 H), 3.07-3.03 (m, 1 H), 2.88-2.75 (m, 2 H), 1.70-1.68 (m, 1 H), 1.50-1.47 (m, 1 H), 1.11-1.09 (m, 1 H), 0.90-0.83 (m, 6 H). 13C NMR (CDCl3, 100 MHz): δ = 160.31, 138.51, 136.14, 130.46, 128.53, 128.33, 128.25, 126.87, 126.50, 76.69, 40.04, 28.38, 27.50, 25.41, 15.63, 11.51. HRMS-ESI: m/z calcd for C20H25NSe + H+: 360.1230; found: 360.1224.
4e: Yield: 76%; [α]D 20 +52 (c 0.7, CH2Cl2). 1H NMR (CDCl3, 400 MHz): δ = 8.16 (s, 1 H), 7.72-7.71 (m, 2 H), 7.47-7.15 (m, 8 H), 3.34-2.96 (m, 3 H), 2.04-1.99 (m, 1 H), 0.95-0.91 (m, 6 H). 13C NMR (CDCl3, 100 MHz): δ = 160.68, 136.07, 133.55, 132.30, 130.82, 130.43, 129.34, 128.87, 126.46, 77.00, 32.74, 32.42, 19.71, 18.57. HRMS-ESI: m/z calcd for C18H21NSe + H+: 332.0911; found: 332.0915.
4f: Yield: 78%; [α]D 20 = +23 (c 0.6, CH2Cl2). 1H NMR (CDCl3, 400 MHz): δ = 8.60 (s, 1 H), 7.99-7.97 (m, 1 H), 7.35-7.16 (m, 6 H), 6.97-6.88 (m, 2 H), 3.88 (s, 3 H), 3.76-3.69 (m, 2 H), 3.01-2.99 (m, 1 H), 2.87-2.77 (m, 2 H), 1.95-1.90 (m, 1 H), 0.89 (d, 6 H, J = 6,72). 13C NMR (CDCl3, 100 MHz): δ = 158.80, 156.24, 139.60, 131.60, 128.90, 128.27, 127.52, 126.42, 124.68, 120.70, 111.56, 77.87, 55.50, 33.26, 28.32, 27.37, 19.71, 18.81. HRMS-ESI: m/z calcd for C20H25NOSe + H+: 376.1179; found: 376.1189.
4g: Yield: 90%; [α]D 20 +71 (c 0.58, CH2Cl2). 1H NMR (CDCl3, 400 MHz): δ = 8.09 (s, 1 H), 7.71-7.69 (m, 2 H), 7.29-7.16 (m, 5 H), 7.00-6.91 (m, 2 H), 3.81 (s, 3 H), 3.75-3.67 (m, 2 H), 2.95-2.76 (m, 3 H), 1.93-1.89 (m, 1 H), 0.94-0.81 (m, 6 H). 13C NMR (CDCl3, 100 MHz): δ = 161.51, 159.61, 139.62, 131.91, 129.95, 129.80, 129.17, 128.31, 126.47, 114.30, 113.93, 77.91, 55.50, 33.37, 28.80, 28.48, 19.72, 18.72. HRMS-ESI: m/z calcd for C20H25NOSe + H+: 376.1179; found: 376.1193.
4h: Yield: 88%; [α]D 20 +52 (c 0.75, CH2Cl2). 1H NMR (CDCl3, 400 MHz): δ = 8.57 (s, 1 H), 8.03-8.01 (m, 1 H), 7.37-7.19 (m, 8 H), 3.85 (s, 2 H), 3.01-2.97 (m, 1 H), 2.89-2.74 (m, 2 H), 1.94-1.92 (m, 1 H), 0.94-0.88 (m, 6 H). 13C NMR (CDCl3, 100 MHz): δ = 157.05, 139.41, 134.99, 133.25, 131.22, 129.61, 128.87, 128.60, 128.50, 126.85, 126.50, 77.32, 33.15, 28.43, 27.40, 19.62, 18.53. HRMS-ESI: m/z calcd for C19H22NClSe + H+: 380.070; found: 380.0856.
4i: Yield: 80%; [α]D 20 +61 (c 0.9, CH2Cl2). 1H NMR (CDCl3, 400 MHz): δ = 8.10 (s, 1 H), 7.70-7.67 (m, 3 H), 7.38-7.21 (m, 6 H), 3.70 (dd, 2 H, J = 12, J = 16), 2.95-2.73 (m, 3 H), 1.94-1.86 (m, 1 H), 0.89-0.86 (m, 6 H). 13C NMR (CDCl3, 100 MHz): δ = 158.98, 139.47, 136.40, 134.63, 129.42, 128.90, 128.78, 128.71, 128.54, 128.35, 126.56, 77.85, 33.36, 28.60, 27.81, 19.66, 19.61. HRMS-ESI: m/z calcd for C19H22NClSe + H+: 380.0684; found: 380.0673.

14

General Procedure for the Allylic Alkylation of 1,3-Diphenyl-2-propenyl Acetate with Dimethyl Malonate: A solution of [PdCl(η3-C3H5)]2 (50 µmol) and chiral ligand (5 mmol%) in dichloromethane (1.5 mL) was stirred for 30 min at r.t. Subsequently, a solution of rac-1,3-diphenyl-2-propenyl acetate (1.0 mmol), dimethyl malonate (3.0 mmol), BSA (3.0 mmol), and KOAc (3 mg, cat. quantity) in dichloromethane (0.8 mL) were added. The reaction mixture was stirred for 48 h. After this time, sat. NH4Cl (aq) was added to quench the reaction, followed by extraction with dichloromethane (3 × 15 mL). The combined organic layers were dried over MgSO4. The solvent was removed in vacuo. The yield was determined by isolated product and the ee by HPLC (Chiralcel OD, 0.5% 2-propanol-hexane, flow 0.5 mL/min, λ = 254nm).