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.
Key words
cyclic ethers - dichlorides - alumina - microwave - solvent-free
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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 1 H NMR and the NMR yield was used only
to determine optimal conditions.
<A NAME="RU01702ST-10">10 </A>
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.
<A NAME="RU01702ST-11">11 </A>
Mass spectrometric analysis was performed
on a Varian SATURN 2000 instrument and the result was obtained as follows: 16 O-phthalan;
MS (EI): m/z (%) = 121
(3), 120 (M+ , 10), 119 (40), 118 (2), 117 (1);
a mixture of 16 O-phthalan and 18 O-phthalan;
MS (EI): m/z (%) = 123
(1), 122 (3) (18 O - M+ ),
121 (12), 120 (8) (16 O - M+ ),
119 (29), 118 (1), 117 (1), 116 (1).