Epoxidation of 4-Alkylidenecyclopentenones

Abstract

The exocyclic double bonds of 4-alkylidenecyclopentenones are selectively epoxidized by MCPBA to give epoxy-cyclopentenones, which under acidic conditions undergo ring-opening to furnish diols.

cyclopentenones - dienones - epoxides - diols

References and Notes

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Typical Procedure (Table [1] , entry 3): To a stirred solution of cyclopentenone 3c (207 mg, 1 mmol) in toluene (8 mL) at 0 °C, was added MCPBA (50%; 690 mg, 2 mmol). The mixture was warmed to r.t. and stirred for 5 h. The mixture was diluted with H₂O and extracted with Et₂O. The combined extracts were washed with a solution of NaHCO₃, brine and then dried over anhyd MgSO₄. After filtration, the solution was concentrated under vacuum. Purification of the crude product by flash chromatography (silica gel, petroleum ether-Et₂O, 80:20) provided epoxycyclopenten-one 4c (180 mg, 81%) as a yellow oil. 4c: R _f 0.33 (petroleum ether-Et₂O, 70:30). IR (thin film): 2860, 2820, 1660, 1650, 1400, 1375, 1250, 1165, 915, 790 cm^-1. ¹H NMR (300 MHz, CDCl₃): δ = 3.26 (t, ³ J = 5.6 Hz, 1 H), 2.56 (d, ² J = 19.0 Hz, 1 H), 2.41 (d, ² J = 19.0 Hz, 1 H), 1.80 (s, 3 H), 1.78 (s, 3 H), 1.20-1.60 (m, 10 H), 0.88 (t, ³ J = 6.6 Hz, 3 H). ¹³C NMR (75 MHz, CDCl₃): δ = 204.5 (C=O), 165.4 (Cq), 141.8 (Cq), 66.0 (CqO), 60.5 (CHO), 37.6 (COCH₂), 32.1 (CH₂), 31.1 (CH₂), 29.5 (CH₂), 26.6 (CH₂), 22.9 (CH₂), 14.4 (CH₃), 10.7 (CH₃), 8.8 (CH₃). MS (ES): m/z = 223 (MH⁺), 445 (2 M + H⁺).

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Acetoxycyclopentenone 3e was prepared by acetylation of the corresponding hydroxymethylcyclopentadienone obtained by the Pauson-Khand cycloaddition of acetylene to 2-methyl-2,3-butadien-1-ol: Ahmar, M.; Thomé, S.; Cazes, B. unpublished result.

<A NAME="RD33505ST-17">17</A>

4e: IR (thin film, trans/cis): 3077, 2937, 1718 (OC=O), 1685 (C=O), 1578, 1376, 1230, 1040, 967, 811, 719 cm^-1. trans-4e ¹H NMR (300 MHz, CDCl₃): δ = 7.29 (d, ³ J = 5.8 Hz, 1 H), 6.46 (d, ³ J = 5.8 Hz, 1 H), 4.14 (d, ² J = 12.5 Hz, 1 H), 4.09 (d, ² J = 12.5 Hz, 1 H), 2.71 (d, ² J = 19.2 Hz, 1 H), 2.47 (d, ² J = 19.2 Hz, 1 H), 2.09 (s, 3 H), 1.49 (s, 3 H). ¹³C NMR (75 MHz, CDCl₃): δ = 204.1 (C=O), 170.6 (OC=O), 158.4 (=CH), 139.5 (=CH), 69.4 (CqO), 67.3 (CH₂OAc), 63.9 (CqO), 38.1 (COCH₂), 20.8 (OCCH₃), 16.2 (CH₃). cis-4e ¹H NMR (300 MHz, CDCl₃): δ = 7.34 (d, ³ J = 6.0 Hz, 1 H), 6.43 (d, ³ J = 6.0 Hz, 1 H), 4.27 (d, ² J = 12.0 Hz, 1 H), 4.20 (d, ² J = 12.0 Hz, 1 H), 2.67 (d, ² J = 19.2 Hz, 1 H), 2.44 (d, ² J = 19.2 Hz, 1 H), 2.09 (s, 3 H), 1.45 (s, 3 H). ¹³C NMR (75 MHz, CDCl₃): δ = 204.1 (C=O), 170.5 (OC=O), 158.3 (=CH), 139.4 (=CH), 69.7 (CqO), 65.8 (CH₂OAc), 63.9 (CqO), 38.1 (COCH₂), 20.8 (OCCH₃), 16.2 (CH₃).

<A NAME="RD33505ST-18">18</A> Lactone 6 seems to be the only six-membered 4-alkylidene-enol lactone described in the literature: Otieno DA. Pattenden G. Popplestone CR. J. Chem. Soc., Perkin Trans. 1  1977,  196 

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