Solvent-Free Synthesis of Cyclic Ethers from Dihalo Compounds in the Presence of Alumina

Abstract

Facile synthesis of cyclic ethers from dihalo compounds on alumina has been accomplished in good yields. The reactions proceeded smoothly both in refluxing hexane and by microwave irradiation in the absence of solvent. In addition to being an organic-solvent-free operation, it also entails a short reaction time.

cyclic ethers - dichlorides - alumina - microwave - solvent-free

References

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8c

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9

Method B: A typical procedure is as follows: A suspension of neutral activated alumina (10 g) in hexane (20 mL) and α,α′-dichloro-o-xylene (1a) (1 mmol) was stirred for 1 h at reflux temperature. The alumina was then removed from the reaction mixture by filtration and washed with ether (100 mL). After the combined filtrate was concentrated in vacuo and purified by distillation, phthalan (2a) was isolated in 64% yield. The yield was also checked by means of ¹H NMR and the NMR yield was used only to determine optimal conditions.

10

Method A: A typical procedure is as follows: A mixture of α,α′-dichloro-o-xylene (1a) (1 mmol) and alumina (10 g) was placed in a beaker (200 mL) and irradiated by micro-wave with a National NE-NS4 (500 W) for 10 min. After extracting the reaction mixture with ether (100 mL) from the alumina, the extract was condensed with an evaporator and separated by flash chromatography on silica to give phthalan (2a) in 69% yield. The final temperatures after microwave irradiation were as follows: 500 W, 10 min: 136 °C; 500 W, 6 min: 102 °C; 500 W, 5 min: 90 °C; 300 W, 15 min: 92 °C.

11

Mass spectrometric analysis was performed on a Varian SATURN 2000 instrument and the result was obtained as follows: ¹⁶O-phthalan; MS (EI): m/z (%) = 121 (3), 120 (M⁺, 10), 119 (40), 118 (2), 117 (1); a mixture of ¹⁶O-phthalan and ¹⁸O-phthalan; MS (EI): m/z (%) = 123 (1), 122 (3) (¹⁸O - M⁺), 121 (12), 120 (8) (¹⁶O - M⁺), 119 (29), 118 (1), 117 (1), 116 (1).