Stille Reactions of 2,3-Bis(stannyl)butenoates: An Unexpected Regioselectivity

Abstract

The palladium-catalyzed cross-coupling reaction of ­methyl (Z)-2,3-bis(tributylstannyl)butenoate with aryl iodides is ­regioselective, leading to 2-aryl-3-stannylated products; this selectivity is the opposite to that observed in the reaction between halides and 3,4-bis(stannyl)furan-2(5H)-one. Since the resulting butenoates can be converted into the corresponding furanones, the method ­provides useful flexibility in the preparation of functionalized butenoates and furanones.

Key words

furanone - Stille coupling - regioselective - bisstannane

References and Notes

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• 2 Carter NB. Mabon R. Richecœur AME. Sweeney JB. Tetrahedron  2002,  58:  9117 
• For other routes to 3,4-disubstituted furanones, see:
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4

Representative Experimental Procedure.
To a flame-dried flask (under an argon atmosphere) charged with methyl (Z)-4-(tetrahydropyran-2-yloxy)-2,3-bis(tri-butylstannyl)but-2-enoate (3, 300 mg, 0.38 mmol) was added dry, deoxygenated THF (3.0 mL), PdCl₂ (PPh₃)₂
(2 mol%), CuI (8 mol%) and AsPh₃. The reaction mixture was then warmed to 50 °C and 4-iodotoluene (101 mg, 0.38 mmol) was added dropwise via syringe, as a solution in THF (2.0 mL). After 18 h, the mixture was allowed to cool, and the mixture was concentrated under reduced pressure. Column chromatography on silica gel (eluent 80:20 PE-Et₂O) gave 4b as a colorless oil (128 mg, 58%); R _f = 0.48 (60:40 PE-Et₂O). IR (neat): ν_max = 2852, 1712, 1612 cm^-1. ¹H NMR (250 MHz, CDCl₃): δ = 0.43-1.54 (27 H, m), 1.66 (3 H, s), 1.58-1.99 (6 H, m), 3.50-3.60 (1 H, m), 3.62 (3 H, s), 3.76-3.80 (1 H, m), 4.25 (1 H, d, J = 14.0 Hz), 4.59-4.63 (1 H, m), 4.59 (1 H, d, J = 14.0 Hz), 6.99-7.07 (4 H, app s). ¹³C NMR (60 MHz, CDCl₃): δ = 10.6, 12.7, 18.5, 24.4, 25.6, 25.8, 26.5, 28.2, 50.7, 62.2, 70.4, 97.7, 127.0, 136.5, 136.7, 140.7, 158.4, 166.8. MS (CI, NH₃): m/z (%) = 523 (85), 308 (100), 85 (80). HRMS: m/z calcd for C₂₅H₄₀O₄Sn: 523.1879. Found: 523.1876 [M - Bu]⁺.