[67707-64-6]  · C8H18Si  · (a,a-Dimethylallyl)trimethylsilane  · (MW 142.32)

(regiospecific prenylation of acetals;2 precursor of substituted tetrahydrofurans via reactions with carbonyl compounds2)

Solubility: sol common organic solvents.

Analysis of Reagent Purity: 1H NMR.

Preparative Methods: treatment of Trichlorosilane with 3-methylbut-2-en-1-ylmagnesium chloride followed by Methylmagnesium Bromide (2 equiv) provides (a,a-dimethylallyl)dimethylsilane (bp 108 °C) in 76% yield with 99% isomeric purity. The hydrosilane is converted to the ethoxysilane quantitatively by the reaction with ethanol catalyzed by Hydrogen Hexachloroplatinate(IV), and then fluorinated in situ with Tetrafluoroboric Acid to give the fluorosilane in 87% yield. The latter is methylated with a small excess of Methyllithium to give (a,a-dimethylallyl)trimethylsilane in 96% yield.2 Alternatively, (a,a-dimethylallyl)trimethylsilane can be prepared from 3-methylbut-1-yn-3-ol in six steps.3

Purification: distillation.

Handling, Storage, and Precautions: can be stored in a glass bottle.

Prenylation of Acetals.

(a,a-Dimethylallyl)trimethylsilane reacts with acetals in the presence of a Lewis acid to give the corresponding homoallyl alcohols with complete regioselectivity (eqs 1 and 2). The reaction with carbonyl compounds often leads to the formation of tetrahydrofuran derivatives (eq 3), presumably through the formation of chloride.2

Cycloaddition with Silyl Shift.

The reaction of (a,a-dimethylallyl)trimethylsilane with 4-Phenyl-1,2,4-triazoline-3,5-dione gives a cycloaddition product where the trimethylsilyl group undergoes a 1,2-shift (eq 4).4

Photochemical Prenylation.

Photolysis of (a,a-dimethylallyl)trimethylsilane in the presence of 1-methyl-2-phenyl-1-pyrrolinium perchlorate leads to the formation of a (3,3-dimethylprop-2-en-1-yl)pyrrolidine as the sole regioisomer (eq 5).5


(a,a-Dimethylallyl)trimethylsilane can undergo isomerization to (g,g-dimethylallyl)trimethylsilane with fluoride ion catalysis.6

1. Fieser, M. FF 1980, 8, 181.
2. Hosomi, A.; Sakurai, H. TL 1978, 2589.
3. Bennetau, B.; Pillot, J.-P.; Dunogues, J.; Calas, R. CC 1981, 1094.
4. Cai, J.; Davies, A. G. JCS(P2) 1992, 1743.
5. Ohga, K.; Yoon, U. C.; Mariano, P. JOC 1984, 49, 213.
6. Hosomi, A.; Shirahata, A.; Sakurai, H. CL 1978, 901.

Hideki Sakurai

Tohoku University, Sendai, Japan

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