t-Butyl a-Lithiobis(trimethylsilyl)acetate

[62803-13-8]  · C12H27LiO2Si2  · t-Butyl a-Lithiobis(trimethylsilyl)acetate  · (MW 266.46)

(forms bis(trimethylsilyl)ketene at 25 °C; reacts with aldehydes to form a-silylated vinyl esters)

Preparative Method: an approximately 1 M solution in THF is prepared by addition of t-butyl bis(trimethylsilyl)acetate to a 1.0 M solution of Lithium Diisopropylamide maintained at -78 °C. The solution is stirred for 1 h at -78 °C following complete addition.1 A simplified procedure utilizes n-Butyllithium in place of LDA and produces the amine-free reagent in THF/hexane.2

Formation of a Ketene.

Solutions of the reagent (1) decompose smoothly in THF at 25 °C to provide a useful synthesis of bis(trimethylsilyl)ketene (eq 1).3

Reaction with Aldehydes.

The reagent reacts via a Peterson alkenation process with aldehydes to give t-butyl 2-trimethylsilyl-2-alkenoates (2) (eq 2).1,4 Only the 1,2-addition product is obtained with 2-butenal (eq 3). The reaction fails with ketones; only a proton transfer reaction to produce the ketone enolate is observed.

The (E) isomer of (2) is normally the favored product,2,5 but selectivity for the (Z) isomer, especially with bulky aldehydes such as pivaldehyde, can be obtained by reaction in the presence of Magnesium Bromide or Diethylaluminum Chloride (eq 4).5

The products (2) are desilylated with Tetra-n-butylammonium Fluoride to produce an allenolate anion (3) which can be trapped in situ by protonation or reaction with aldehydes (eq 5).2

Related Reagents.

t-Butyl Trimethylsilylacetate; Ethyl Lithio(trimethylsilyl)acetate; Ethyl 2-(Methyldiphenylsilyl)propanoate; Ethyl Trimethylsilylacetate; Methyl 2-Trimethylsilylacrylate; Trimethylsilylacetic Acid.

1. Hartzell, S. L.; Rathke, M. W. TL 1976, 2737.
2. Sato, Y.; Takeuchi, S. S 1983, 734.
3. Sullivan, D. F.; Woodbury, R. P.; Rathke, M. W. JOC 1977, 42, 2038.
4. For reviews on the Peterson alkenation see: Ager, D. J. S 1984, 384; OR 1990, 38, 1.
5. Boeckman, Jr., R. K.; Chinn, R. L. TL 1985, 26, 5005.

Michael Rathke & Robert Elghanian

Michigan State University, East Lansing, MI, USA

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