[2345-38-2] · C5H12O2Si · Trimethylsilylacetic Acid · (MW 132.26)
(preparation of a,b-unsaturated carboxylic acids and a-trimethylsilylbutyrolactones2)
Physical Data: mp 40 °C.
Solubility: sol ethereal solvents.
Preparative Methods: obtained from the reaction of Trimethylsilylmethylmagnesium Chloride with Carbon Dioxide;3 can also be prepared by reaction of Acetic Acid with 2 equiv of Lithium Diisopropylamide, followed by Chlorotrimethylsilane and hydrolysis.4
Handling, Storage, and Precautions: prone to isomerization and should not be stored for extensive periods.
In a manner similar to a-silyl esters, trimethylsilylacetic acid (1) can be used to prepare a,b-unsaturated carboxylic acids from carbonyl compounds by a Peterson alkenation reaction (eq 1).1 However, the dianion of acid (1) is required.2 The yields are generally inferior to analogous reactions with a-silyl esters.5
The dianion of acid (1) also reacts with alkyl halides to afford substituted a-trimethylsilylcarboxylic acids.2 With epoxides, the dianion provides g-hydroxy acids that cyclize to a-silylbutyrolactones (eq 2).2 The resultant a-silyl lactones (2) are precursors to a wide variety of functionalized derivatives. The direct conversion of a butyrolactone to its a-silyl analog is complicated by the competition of the O-silylation pathway.
Trimethylsilylacetyl thiolesters, which have been used as precursors to b-lactams, are prepared by reaction of the appropriate thiol with the acid chloride derivative of (1).6 Acid (1) has also been used as a precursor to 1-diazo-3-trimethylsilylacetone, which provides cyclopropyl trimethylsilylmethyl ketones upon reaction with alkenes, through reaction of the acid chloride or a mixed anhydride derivatives of the acid (1) with Diazomethane.4
Silylacetic acids undergo a thermal rearrangement to afford the silyl ester (eq 3). The same migration of the silyl group is observed at lower temperatures when base catalysis is employed.7
David J. Ager
The NutraSweet Company, Mount Prospect, IL, USA