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Olefination of 3-phenyl-6-bromoindene; benzofulvene

SyntheticPage 697
DOI: 10.1039/SP697
Submitted Oct 01, 2013, published Oct 04, 2013
Adam Glass (glassac@plu.edu), Valerie Lesniak (lesniava@plu.edu)
A contribution from GlassLab, Pacific Lutheran University


			Reaction Scheme: <IMG src="/images/empty.gif"><IMG src="/images/empty.gif">Olefination of <SPAN id=csm1397736410527 class=csm-chemical-name title=3-phenyl-6-bromoindene grpid="2">3-phenyl-6-bromoindene</SPAN><IMG src="/images/empty.gif"><IMG src="/images/empty.gif">

Chemicals Used

Indene 1 (Prepared in House by method of SP696)

n-BuLi (2.5 M solution in hexanes, Acros Organics)

p-tolualdehyde (TCI)

2-MeTHF (≥99%, Anhydrous, Sigma-Aldrich)

Diethyl Ether (Sigma-Aldrich)

Dichloromethane (Sigma-Aldrich)

Saturated Ammonium Chloride

Procedure

Procedure A: The synthesis was performed using standard Schlenk techniques under a nitrogen atmosphere. To a sealed scintillation vial charged with indene 1 (43.7 mg, 0.161 mmol), anhydrous 2-MeTHF (1.6 mL) was added. The solution was cooled to 0 oC and n-BuLi (0.070 mL, 0.161 mmol, 2.5 M solution in hexanes) was added dropwise. The reaction mixture was then stirred for 1 h. p-tolualdehyde (0.020 mL, 0.169 mmol) was added to the reaction mixture at 0 oC. The reaction mixture was returned to RT and stirred for 20 h. TLC was used to monitor the reaction.* The reaction mixture was quenched and washed with saturated ammonium chloride (3 x 1 mL) and extracted with diethyl ether (3 x 1 mL). The organic layer was dried over magnesium sulfate, filtered into a roundbottom flask, and further eluted with diethyl ether (3 mL). The solvent was evaporated under reduced pressure. The crude product was dissolved in dichloromethane and purified using a preparatory plate (90:10, hexanes:toluene), yielding a light red solid, benzofulvene 2 (28.7 mg, 47%).

Procedure B: The synthesis was performed using standard Schlenk techniques under a nitrogen atmosphere. To a sealed scintillation vial charged with indene 1 (100 mg, 0.369 mmol), anhydrous heptane (3.7 mL) was added. The solution was cooled to 0 oC and n-BuLi (0.15 mL, 0.369 mmol, 2.5 M solution in hexanes) was added dropwise. The reaction mixture was warmed to RT and stirred overnight.  A tan precipitate develops.  The heptanes was removed under reduced pressure and anhydrous 2-MeTHF (3.7 mL) was added.  The solution was cooled to 0 oC and p-tolualdehyde (0.048 mL, 0.406 mmol) was added dropwise. The reaction mixture was returned to RT and stirred for 20 h. TLC was used to monitor the reaction.* The reaction mixture was quenched and washed with saturated ammonium chloride (3 x 2 mL) and extracted with diethyl ether (3 x 2 mL). The organic layer was dried over magnesium sulfate, filtered into a roundbottom flask, and further eluted with diethyl ether (3 mL). The solvent was evaporated under reduced pressure. The crude product was dissolved in dichloromethane and purified using a preparatory plate (90:10, hexanes:toluene), yielding a light red solid, benzofulvene 2 (81.0 mg, 59%).

*An aliquot was removed from the crude reaction mixture and diluted for TLC.

Author's Comments

Butyl lithium is pyrophoric.  It should be handled under inert conditions.

The synthesis using heptanes as the solvent for the lithiation step (Procedure B) was determined to be more reproducible.  Arguably due to acid/base chemistry between n-BuLi and 2-MeTHF.

Benzofulvenes are highly colored molecules.  Chromatography is a excellent route for purification as the desired compound can be observed directly during purification.    

 A saturated solution of sodium chloride (Brine) was used to remove emulsions during the washing phases.

Data

1H NMR (CDCl3, 500 MHz): δ ppm 2.54 (s, 3H), 7.27 (s, 1H), 7.38-7.39 (m, 2H), 7.51-7.61 (m, 6H),  7.69 (d, J = 8.3 Hz, 2H), 7.77-7.79 (m, 2H), 8.00 (s, 1H)

13C NMR (CDCl3, 125 MHz): δ ppm 21.66, 119.76, 121.27, 122.86, 123.67, 128.54, 128.54, 128.97, 129.88, 129.94, 129.98, 130.60, 134.15, 135.61, 137.57, 139.38, 139.57, 141.25, 146.72

GC-MS EI [M.+]: Predicted: 372.05, Actual: 372; Predicted: 374.06, Actual: 374; Predicted: 373.05, Actual: 373


Lead Reference


Other References

Lu, W.; Zhu, Q.; Yan, C. Synth. Commun., 1997, 27, 3985-3990.

Alcalde, E.; Mesquida, N.; Frigola, J.; López-Pérez, S.; Mercè, R. Org. Biomol. Chem., 2008, 6, 3795-3810

Supplementary Information

e.g. Actual NMR spectra (as images or jdx files for interactive spectra), photographs of apparatus, TLC’s or crystals or videos. Please contact the ChemSpider team (ChemSpider-at-rsc.org) for help with this.
1H NMR.pdf
13C NMR.pdf
GC-MS.pdf
1H NMR.esp
13C NMR.esp

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Keywords: aldehydes, aromatics/arenes, Li, nucleophilic, organometallics