[18269-31-3] · C7H14O2Si · Methyl 2-Trimethylsilylacrylate · (MW 158.30)
(reactive, a-silyl Michael acceptor for conjugate addition of carbanions, enolate anions, organolithium reagents, and Grignard reagents; affords 3-cyclopentenecarboxylates and cyclohexanecarboxylates by [3 + 2] and [4 + 2] annulation methods; provides a-silyl esters and vinylsilanes by organolithium conjugate additions1,3,5)
Physical Data: bp 75 °C/50 mmHg, 152 °C/690 mmHg.
Solubility: sol Et2O, THF, EtOH, and most organic solvents.
Analysis of Reagent Purity: IR, NMR, GC.
Preparative Methods: prepared2a,b by the reaction of (E)-2-(Trimethylsilyl)vinyllithium with Methyl Chloroformate or by carbonation of the corresponding Grignard reagent prepared from (1-Bromovinyl)trimethylsilane,2c giving 2-trimethylsilylacrylic acid. The methyl ester is prepared from the acid by direct esterification with absolute methanol in the presence of mineral acid, by reaction with Diazomethane at low temperature, or by treatment with BF3.MeOH complex. For preparation of various trialkylsilylacrylic acid esters2d and t-butyl 2-trimethylsilylcrotonate,8 see the cited references.
Handling, Storage, and Precautions: should be stored in a refrigerator and addition of a few crystals of ionol is recommended in order to prevent polymerization. Use in a fume hood.
Conjugate addition of allylithium reagents bearing stabilizing groups in the a- and b-positions to methyl 2-trimethylsilylacrylate leads to an anionic [3 + 2] cyclization,3a,b generating the trimethylsilyl-substituted 3-cyclopentenecarboxylate in 57% yield (eq 1). a-Unsubstituted Michael acceptors do not give good yields of the cyclopentene product.
The kinetic enolate of 1-acetylcyclohexene on reaction with methyl 2-trimethylsilylacrylate undergoes a two-fold Michael addition, giving rise to 5-substituted 1-decalones (eq 2), one of which was converted to (±)-khusitone4a and (±)-khusilal.4b
In another annulation sequence,5 a functionalized aryllithium generated chemoselectively from (2-bromo-4,5-dimethoxyphenyl)ethyl bromide at -100 °C undergoes conjugate addition with methyl 2-trimethylsilylacrylate, and the adduct cyclizes by intramolecular alkylation to give the tetrahydronaphthalenecarboxylate in 80% yield (eq 3).
Conjugate addition of organometallic reagents (magnesium or lithium) to methyl 2-trimethylsilylacrylate gives either 1:1 or 1:2 adduct6c anions (eq 4), depending upon the reaction conditions and reactivity of donor molecules. These anions undergo either alkylation6b with a suitable alkylation agent or add to another electrophile6a such as ketones, aldehydes, or a,b-unsaturated aldehydes.
2-Azaallyl anions7 derived from aryl-substituted imines undergo highly diasteroselective Michael addition to methyl 2-trimethylsilylcrotonate. The Michael adducts are converted to pyrrolidones through hydrolytic cyclization (eq 5).
Anubhav P. S. Narula
International Flavors & Fragrances, Union Beach, NJ, USA