Silylation of diethyl ethoxymethylenemalonate with dimethyl(phenyl)silyl lithium; Diethyl [dimethyl(phenyl)silyl]methylenemalonate
SyntheticPage 522
DOI:
10.1039/SP522
Submitted Dec 09, 2011, published Dec 09, 2011
sunil ghosh (
ghsunil@barc.gov.in)
A contribution from
Sunil Ghosh-BARC
Chemicals Used
Lithium (Spectrochem, India)
Chlorodimethylphenylsilane 98% (Aldrich)
THF (Dried and distilled over Na-benzophenone ketyl)
Diethyl ethoxymethylene-malonate >99% (Spectrochem, India)
Diethyl ether
Ammonium chloride
Di Water
Anhy. MgSO4
Procedure
A 0.5 L three-neck round bottomed flask, fitted with a septum, an argon inlet/outlet and a stirring bar was charged with freshly cut fine pieces of lithium metal (from a 5 mm diameter Li-wire, 2.56 g, 366 mmol). The metal pieces were washed once with dry THF (20 ml) with the help of a syringe. Dry THF (200 mL) was introduced into the flask and the stirred suspension was cooled on an ice-water bath. Dimethyl(phenyl)silyl chloride (Aldrich) (26.1 g, 153 mmol) was added drop-wise to the stirred suspension over 10 min and the reaction mixture was stirred under those conditions for 6 h to give a deep red colour solution of the dimethyl(phenyl)silyl lithium.
A separate 1 L three-neck round bottomed flask, fitted with a septum, an argon inlet/outlet and a stirring bar was charged with freshly distilled
diethyl ethoxymethylene-malonate (31 mL, 153 mmol) and dry
THF (350 ml). The stirred solution was cooled on a dry-ice-acetone bath (–78
oC) while the
dimethyl(phenyl)silyl lithium solution was cannulated into it over 0.5 h. After the addition was over, the reaction mixture was stirred for 5 min and the cold bath was removed. The reaction mixture was allowed to attain to room temperature (about 0.5 h) and poured into saturated
ammonium chloride solution (150 mL). The mixture was further diluted with water (200 mL) and extracted with ether (3 × 200 mL). The organic extract was washed with water (2 × 200 mL) and with brine (100 mL), dried (
MgSO4) and evaporated. The residue was distilled to give
diethyl [dimethyl(phenyl)silyl]methylenemalonate (34.2 g, 73%) as a colorless oil; B. p. 125-126
oC (0.08 mmHg)
Author's Comments
The dimethyl(phenyl)silyl lithium reagent is sensitive to air, moisture, temperature and storage. So it should be used immediately after its preparation. While cannulation of the reagent, the bulk lithium reagent should be maintained at ice-bath temperature.
The ether extract can hold good amount of water. So the residue after ether removal may be diluted with hexanes and the separated water layer can be discarded.
Data
B. p. 125-126 oC (0.08 mmHg); 1H NMR (200 MHz, CDCl3) 0.45 (6 H, s), 1.19 (3 H, t, J = 7.1 Hz), 1.29 (3 H, t, J = 7.1 Hz), 4.00 (2 H, q, J = 7.1 Hz), 4.24 (2 H, q, J = 7.1 Hz), 7.31 (1 H, s), 7.34-7.38 (3 H, m), 7.50-7.55 (2 H, m).
Lead Reference
S. K. Ghosh,
R. Singh and S. M. Date,
Chem. Commun.,
2003, 636-637;
DOI: 10.1039/b211279e
Other References
P. Iyer and .K. Ghosh, Tetrahedron Lett., 2002, 43, 9437-9440; S. M. Date, P. Iyer and S. K. Ghosh, Syn. Commun., 2004, 405-411; S. K. Ghosh, R. Singh and G. C. Singh, Eur. J. Org. Chem., 2004, 4141-4147; S. M. Date, R. Singh and .K. Ghosh, Org. Biomol. Chem., 2005, 3, 3369-3378; R. Chowdhury and S. K. Ghosh, Org. Lett., 2009, 11, 3270-3273; R. Chowdhury and S. K. Ghosh, Tetrahedron: Assym., 2010, 21, 2696-2702.
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Keywords: addition, alkenes, dimethyl(phenyl)silyl lithium, elimination, esters, nucleophilic, silylation, substitution
