Synlett 2006(11): 1747-1749  
DOI: 10.1055/s-2006-944209
LETTER
© Georg Thieme Verlag Stuttgart · New York

Double Coupling Reactions of 3,4-Bis(stannyl)furanone: Facile Preparation of Diaryl- and Dibenzylfuranones

Neil B. Carter, Ross Mabon, Rachel Walmsley, Alexandre M. E. Richecœur, J. B. Sweeney*
School of Chemistry, University of Reading, Reading RG6 6AD, UK
Fax: +44(118)3786331; e-Mail: j.b.sweeney@reading.ac.uk;
Further Information

Publication History

Received 7 April 2006
Publication Date:
04 July 2006 (online)

Abstract

The palladium-catalyzed cross-coupling reaction of 3,4-bis(tributylstannyl)furan-2(5H)-one using chelating ligand or polar solvent gives mixtures of single and double coupled products, even when one equivalent of halide coupling partner is used. After optimization, the double coupling reaction was shown to be general, with the use of two equivalents of aryl iodides giving 3,4-disub­stituted furanones, The reaction using benzyl bromides proceeds at lower temperatures than the corresponding coupling using aryl ­iodides, giving dibenzylfuranones. The methodology has been ­exemplified in a synthesis of (±)-hinokinin.

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It is not possible to directly discern the yields of the individual coupling reactions: assuming a maximum yield of 100% for the second coupling (normally a more efficient process, see ref. 2), the maximum possible yield for the first step is 51%. Our original observations in monocoupling of 1 with PhI gave 2 (Ar = Ph) in a yield of 51%.

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Representative Experimental Procedure.
To a flame-dried flask (under argon atmosphere) charged with PdCl2(PPh3)2 (2 mol%), CuI (8 mol%), AsPh3 (8 mol%) was added 3,4-bis(tributylstannyl)furan-2(5H)-one (500 mg, 0.76 mmol) as a solution in dry, deoxygenated DMF, followed by iodobenzene (310 mg, 1.52 mmol), also added dropwise as a solution in DMF (2.0 mL). After reaction was complete (24 h) the mixture was diluted with aq KF (1 M, 10.0 mL) and extracted with Et2O (3 × 30.0 mL), washed with H2O (3 × 15.0 mL) and brine (3 × 15.0 mL). Solvent was removed under reduced pressure and the crude product was purified via flash chromatography (silica gel, 3:2 PE-Et2O; R f = 0.24). Recrystallization (CH2Cl2-PE) gave 3,4-diphenylfuran-2(5H)-one as pale yellow crystals (56%, 101 mg); mp 104-105 °C (CH2Cl2-PE). IR (CHCl3): 1751, 1646, 1489 cm-1. 1H NMR (250 MHz, CDCl3): δ = 5.10 (2 H, s), 7.23-7.33 (10 H, m). 13C NMR (60 MHz, CDCl3): δ = 71.0 (OCH2), 126.6, 127.9, 129.2, 129.3, 129.4, 129.7, 130.6, 131.0, 131.2, 156.6, 173.9. MS (CI, NH3): m/z calcd for C16H13O2: 237.0916. Found [MH]+: 237.0915; m/z (%) = 179.0 (15).

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Representative Experimental Procedure.
To a flame-dried flask (under an argon atmosphere) charged with benzyl bromide (226 mg, 1.33 mmol), PdCl2(PPh3)2 (5 mol%), AsPh3 (8 mol%) and CuI (8 mol%) was added THF (5.0 mL) and the mixture warmed to 50 °C. 3,4-Bis(tributyl-stannyl)furan-2(5H)-one (450 mg, 0.66 mmol) in THF (5.0 mL) was added dropwise via syringe. After reaction was complete the mixture was concentrated under reduced pressure. Purification via flash chromatography (silica gel, PE-Et2O 1:1; R f = 0.50) gave 3,4-dibenzylfuranone as a clear colorless oil (78 mg, 45%). IR (CHCl3): 3063, 1754, 1668 cm-1. 1H NMR (250 MHz, CDCl3): δ = 3.71 (2 H, s), 3.74 (2 H, s), 4.51 (2 H, s), 6.99-7.02 (2 H, dd, J = 7.0, 2.0 Hz), 7.22-7.29 (8 H, m). 13C NMR (60 MHz, CDCl3): δ = 30.0, 34.0, 71.7, 127.0, 127.2, 127.7, 129.0, 129.1, 129.2, 129.5, 136.3, 138.5, 160.3, 175.2. MS (CI, NH3): m/z calcd for C18H16O2: 265.1231. Found [MH]+: 265.1221; m/z (%) = 219 (20), 91 (25).

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Data for (±)-Hinokinin.
IR (CHCl3): 1769, 1495, 1245, 1033 cm-1. 1H NMR (400 MHz, CDCl3): δ = 2.45-2.60 (3 H, m, ArCH2CH, ArCH2CH and ArCH2CHCHC=O), 2.86 (1 H, dd, J = 14.5, 7.0 Hz, ArCH2CHC=O), 2.99 (1 H, dd, J = 14.0, 5.0 Hz, ArCH2CHC=O), 3.87 (1 H, dd, J = 9.00, 7.00 Hz, OCH2), 4.14 (1 H, dd, J = 10.0, 7.00 Hz, OCH2), 5.95 (4 H, m, OCH2O), 6.46-4.48 (2 H, m, 2 × Ar,), 6.62 (2 H, m, 2 × Ar), 6.64 (2 H, m, 2 × Ar). 13C NMR (100 MHz, CDCl3): δ = 35.2, 38.8 (ArCH2), 41.7 (ArCH2CHCHC=O), 46.9 (ArCH2CHCHC=O), 71.6 (OCH2), 101.4 (OCH2O) 108.6, 108.9, 109.2, 109.8, 121.9, 122.6, 131.7, 132.0, 132.1, 146.8, 146.9, 148.3 (2 × Ar), 178.8 (C=O). MS (CI, NH3): m/z calcd for C20H19O6: 355.1181. Found [MH]+: 355.1164; m/z (%) = 135 (45).