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1996
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November
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In the Laboratory
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The Microscale Laboratory
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Microscale Preparation of Difluorenylidene and trans-2,3-Dibenzoylspiro[cyclopropane-1-99-fluorene]
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Fred H. Greenberg
SUNY College at Buffalo, Buffalo, NY 14222
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November 1996
Vol. 73 No. 11
p. 1043
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| Abstract |
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The synthetic sequence involving the oxidation of fluorene to fluorenone and the reduction of fluorenone to fluorenol can be extended by preparing the title compounds via the intermediate 9-chlorofluorene. The latter is obtained by heating fluorenol in methanol with conc. hydrochloric acid. Difluorenylidene (1), a conjugated, orange-red hydrocarbon, is prepared by adding potassium hydroxide in sulfolane/methanol to a sulfolane solution of 9-chlorofluorene, waiting several minutes, adding water to precipitate 1, centrifuging, washing with water and recrystallizing from dichloromethane/ethanol. A most likely mechanism is deprotonation at C-9 followed by SN2 displacement of chloride ion by the anion of 9-chlorofluorene to give an intermediate that undergoes E2 elimination to generate (1). The reaction done in methanolic potassium hydroxide solution affords 9-methoxyfluorene and
demonstrates sulfolane's ability to enhance base strength and promote the first mechanistic step. Student yields range from 5 to 25 mg (12% - 61%) and average 30%. The product that emerges on heating a sulfolane solution of equimolar quantities of 9-chlorofluorene, base, and trans-dibenzoylethylene, is not 1, but trans-2,3-dibenzoylspiro[cyclopropane-1,9'-fluorene] (2). The reaction is an example of tandem cycloaddition, a standard method of cyclopropanation. Student yields are meager, averaging 34%, but the emphasis is on product identification based on the IR, C and 1H NMR spectra.
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| More Information |
 Citation |
Greenberg, Fred H. J. Chem. Educ. 1996 73 1043.
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Keywords |
Organic Chemistry
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History |
Created:
Last Updated: |
August 5, 1999
February 21, 2006
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| Home > JCE Print > Journal of Chemical Education > Issues >
1996
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November
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1043
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