Synlett 2010(10): 1549-1553  
DOI: 10.1055/s-0029-1219936
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

Direct Catalytic Benzylation of Hydroxycoumarin - Efficient Synthesis of Warfarin Derivatives and Analogues

Magnus Rueping*a, Boris J. Nachtsheimb, Erli Sugionoa
a Institute of Organic Chemistry, RWTH Aachen University, Landoltweg 1, 52074 Aachen, Germany
Fax: +49(241)8092665; e-Mail: Magnus.Rueping@rwth-aachen.de;
b Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, 240 Longwood Avenue, Boston, MA 02115, USA
Further Information

Publication History

Received 11 March 2010
Publication Date:
10 May 2010 (online)

Abstract

Effective metal-catalyzed benzylations of 4-hydroxycoumarin have been developed. Employing a low amount of a cheap, nontoxic, and air-stable catalyst the 3-alkylated hydroxycoumarins were isolated in high yields after short reaction times. Applying this new methodology two widely used anticoagulants phenprocoumon and coumatetralyl were synthesized applying mild reaction conditions.

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14

A General Procedure for the Bismuth(III)-Catalyzed Benzylation of 4-Hydroxycoumarin
In a typical experiment 4-hydroxycoumarin (1 mmol) and Bi(OTf)3 (H2O)4 (0.005 mmol, 0.5 mol%) were suspended in DCE (5 mL) and heated to 90 ˚C. Subsequently, 1-phenyl-ethanol dissolved in DCE (1 mL) was added (2.5 mmol) dropwise over 4 h. The resulting clear solution was allowed to cool down to r.t., the solvent evaporated under vacuum, and the crude mixture purified by column chromatography (hexane-EtOAc, 3:1) to afford 248 mg (89%) of 2a.
Selected Data
Compound 2a: white amorphous solid. ¹H NMR (250 MHz, CDCl3): δ = 7.76-7.66 (m, 1 H), 7.62-7.47 (m, 5 H), 7.44-7.22 (m, 3 H), 6.02 (s, 1 H), 4.85-4.72 (q, J = 7.3 Hz, 1 H), 1.72 (d, J = 7.3 Hz, 3 H). ¹³C NMR (75 MHz, CDCl3): δ = 163.4, 159.6, 152.5, 141.5, 131.8, 129.9, 128.0, 127.3, 123.8, 122.9, 116.4, 116.1, 110.1, 34.6, 16.5. IR (neat): ν = 3231 (b), 1669, 1610, 11216, 753 cm. MS (EI): m/z (%) = 266.1 (100)[M]+ , 251.1 (48) [M - CH3]+ , 189.1 (7) [M - C6H5]+ . Anal. Calcd for C17H14O3: C, 76.68; H, 5.30. Found: C, 76.84; H, 5.51.
Compound 2b: white amorphous solid. ¹H NMR (250 MHz, CDCl3): δ = 7.77-7.70 (m, 1 H), 7.63-7.53 (m, 3 H), 7.44-7.26 (m, 4 H), 6.00 (s, 1 H), 4.72 (q, J = 7.3 Hz, 1 H), 1.71 (d, J = 7.3 Hz, 3 H). ¹³C NMR (63 MHz, CDCl3): δ = 163.3, 159.6, 152.6, 140.7, 132.7, 132.1, 129.1, 124.0, 122.8, 116.5, 115.9, 109.7, 34.1, 16.6. IR (neat): ν = 3436 (br), 1716, 1660, 1605, 1203, 754 cm. MS (EI): m/z (%) = 344.0(100) [M]+ , 345.0(22) [M]+ , 346.0(97) [M]+ , 347.0(18) [M]+ . Anal. Calcd for C17H13BrO3: C, 59.15; H, 3.80. Found: C, 58.91; H, 3.90.