Synthesis of Spirocyclic Butenolides by Ring Closing Metathesis

Abstract

Spirocyclic butenolides were efficiently prepared by a ring closing metathesis strategy.

Key words

butenolides - catalysis - metathesis - ruthenium - spiro-compounds

References

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7

Representative Experimental Procedure: To a CH₂Cl₂-solution (30 mL) of 3f (264 mg, 1 mmol) was added Ti(iPrO)₄ (42 mg, 0.15 mmol) and the solution was stirred for 1 h at 35 °C. A CH₂Cl₂-solution (10 mL) of 5 (82 mg, 0.1 mmol) was subsequently added and the reaction mixture was stirred at 35 °C for 48 h. The solvent was removed in vacuo and the residue was purified by column chromatography (silica gel, petroleum ether/ether = 3:1) to give 4f as a white solid (165 mg, 0.70 mmol, 70%). Spectroscopic data of 4f: ¹H NMR (CDCl₃, 250 MHz): δ = 1.23-1.40 (m, 13 H, CH₂), 1.41-1.60 (m, 7 H, CH₂), 1.70-1.82 (m, 2 H, CH₂), 5.95 (d, J = 6 Hz, 1 H, CH), 7.48 (d, J = 6 Hz, 1 H, CH). ¹³C NMR (CDCl₃, 50 MHz): δ = 19.94, 21.79, 22.32, 25.68, 25.96 31.86, 91.87, 119.81, 160.79, 172.43. IR (KBr): ν = 3088 (w), 2957 (s), 2937 (s), 2864 (m), 2847 (m), 1743 (s), 1472 (s), 1444 (m)cm^-1. MS (70 eV): m/z (%) = 236 (100) [M⁺], 208 (16), 179 (12), 165 (28), 151 (28); the exact molecular mass for C₁₅H₂₄O₂ m/z = 236.1776 ± 2 mD [M⁺] was confirmed by HRMS (EI, 70 eV). Anal. Calcd for C₁₅H₂₄O₂: C, 76.23; H, 10.24. Found: C, 76.10; H, 10.76. All new compounds gave satisfactory spectroscopic data and correct elemental analyses and/or high resolution mass data.