Lewis Acid Catalyzed Ring-Opening Reactions of Methylenecyclopropanes with 1,3-Cyclodiones

Abstract

Methylenecyclopropanes undergo an interesting ring-opening reaction with 1,3-cyclodiones upon heating at 85 °C to give the corresponding homoallylic alcohol derivatives in good to high yields in the presence of a Lewis acid.

Key words

methylenecyclopropanes - enols - Lewis acid - ring-opening reaction - 1,3-cyclodiones

References and Notes

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10

General Procedure for the Reaction of 1,1-Diphenyl-methylenecyclopropane ( 1a) with 1,3-Cyclohexadione ( 2a) in the Presence of Sn(OTf) ₂ .
1,1-Diphenylmethylenecyclopropane (1a, 0.30 mmol), 1,3-cyclohexadione (2a, 0.30 mmol) and Sn(OTf)₂ (0.03 mmol) were dissolved in 2.0 mL of DCE. The reaction mixture was stirred at 85 °C for 4 h. Then, the solvent was removed under reduced pressure and the residue was purified by flash column chromatography (SiO₂) to give the corresponding homoallylic alcohol product 3a in 82% yield.
3-(4,4-Diphenylbut-3-enyloxy)cyclohex-2-enone ( 3a).
Colorless solid, mp 78-79 °C. IR (CH₂Cl₂): ν = 3051, 3024, 2945, 2886, 1655, 1604, 1493, 1397, 1366, 1349, 1328, 1219, 1183, 1153, 1014, 761, 701 cm^-1. ¹H NMR (300 MHz, CDCl₃, TMS): δ = 1.93-2.01 (2 H, m, CH₂), 2.34 (2 H, t, J = 6.6 Hz, CH₂), 2.41 (2 H, t, J = 6.6 Hz, CH₂), 2.55 (2 H, dt, J = 6.6, 7.5 Hz, CH₂), 3.89 (2 H, t, J = 6.6 Hz, OCH₂), 5.34 (1 H, s, CH), 6.10 (1 H, t, J = 7.5 Hz, CH), 7.17-7.39 (10 H, m, Ar). ¹³C NMR (75 MHz, CDCl₃, TMS): δ = 21.1, 28.9, 29.1, 36.7, 67.9, 102.8, 123.9, 127.1, 127.2, 127.3, 128.1, 128.3, 129.7, 139.5, 142.0, 144.4, 177.8, 199.7. MS (EI): m/z (%) = 207 (5.57) [M⁺ - 111], 178 (15.16), 151 (100), 129 (47.61), 128 (21.81), 115 (43.64), 91 (95.22), 77 (13.19), 41 (17.35). Anal. Calcd for C₂₂H₂₂O₂: C, 82.99; H, 6.96%. Found: C, 82.83; H, 7.01%.