Cu(OTf)₂-Catalyzed Selective Opening of Aryl and Vinyl Epoxides with Carbonyl Compounds to Give 1,3-Dioxolanes

Abstract

Copper(II) triflate catalyzes the ring-opening of aryl- and vinyl-substituted epoxides with various carbonyl compounds to ­furnish 1,3-dioxolanes under mild conditions. Alkyl- and alkoxycarbonyl-substituted epoxides remain unchanged under reaction conditions. This allows selective opening of aryl-substituted ­epoxides in the presence of alkyl-substituted ones.

Key words

epoxide-opening - dioxolanes - copper triflate - chemo­selectivity

References

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1

New address: P. Krasik, Torcan Chemical Ltd. P.O. Box 308, 110 Industrial Parkway North, Aurora, Ontario, L4G 3H4, Canada; e-mail: [e-mail].

15

Typical catalyst loadings are 2-20 mol%.

17

The competition experiment was carried out as follows: Cu(OTf)₂ (2 mol%) was dissolved in CH₂Cl₂ (1 mL) and dry acetone (1.5 mL, 10 equiv). The reaction mixture was cooled to -20 °C, a mixture of styrene oxide (1 mmol) and 1-butene oxide (1 mmol) was added dropwise. The reaction mixture was stirred for 1 h at -20 °C, poured onto sat. aq NaHCO₃ solution (5 mL). CH₂Cl₂ (10 mL) was added and the organic layer was separated. The reaction mixture was analyzed by ¹H NMR. Complete conversion to 1,3-dioxolane was detected for styrene oxide. 1-Butene oxide remains unchanged.

18

Typical procedure for epoxide-opening with carbonyl compounds is as follows: Cu(OTf)₂ (2 mol%) was dissolved in CH₂Cl₂ (1 mL) and dry acetone (1.5 mL, 10 equiv). The reaction mixture was cooled to -20 °C, styrene oxide (2 mmol) was added dropwise. The reaction mixture was stirred for 1 h at -20 °C, poured onto sat. aq NaHCO₃ solution (5 mL). CH₂Cl₂ (10 mL) was added and the organic layer was separated. The product was purified by flash chromatography (10% EtOAc in hexane) to give 2,2-dimethyl-4-phenyl-1,3-dioxolane in 95% yield. ¹H NMR (400 MHz, CDCl₃): δ = 1.52 (s, 3 H), 1.58 (s, 3 H), 3.72 (dd, J = 8.2, 8.1 Hz, 1 H), 4.34 (dd, J = 8.1, 6.3 Hz, 1 H), 5.10 (dd, J = 7.9, 6.3 Hz, 1 H), 7.20-7.60 (m, 5 H). ¹³C NMR (400 MHz, CDCl₃): δ = 139.48, 128.99, 128.50, 126.68, 110.15, 78.40, 72.14, 27.06, 26.45.

19

For all compounds the physical data corresponded to that published earlier.

20

Conditions: 5 mol% of Cu(OTf)₂, -80 °C, 178 h.