[18740-59-5]  · C21H21ClSi  · Tribenzylchlorosilane  · (MW 336.96)

(reagent for alcohol protection5)

Physical Data: mp 141-142 °C;1,2 a somewhat higher value (143-145 °C) is cited in the Aldrich catalog.

Solubility: sparingly sol cold petroleum ether; moderately sol hot petroleum ether; sol ether.

Form Supplied in: white crystalline solid; commercially available.

Preparative Methods: prepared by reaction of benzylmagnesium chloride with SiCl4 in ether;3 separation from mono- and dibenzylated chlorosilane byproducts is then accomplished by fractional distillation (boiling range 300-360 °C/100 mmHg). Other preparations involve the chlorination of tribenzylsilane using Cl21 or an acyl chloride.1,3 No yields are reported for any of the above preparative procedures.

Purification: can be recrystallized from petroleum ether.2

Handling, Storage, and Precautions: corrosive; should be handled with caution. It does not fume perceptibly in air,2 but it is moisture sensitive and is slowly decomposed by water over several hours to give the corresponding silanol.3

Protection of Alcohols.

Tribenzylchlorosilane is highly reactive towards nucleophilic displacement of chloride ion,4 but it has found only limited application as a bulky silyl protecting group for alcohols. The protection of the allylic alcohol (1) as the tribenzylsilyl ether (2) (eq 1) allowed for high p-facial selectivity in a subsequent epoxidation reaction at the 10,11-double bond.5 The tribenzylsilyl ether group can be efficiently deprotected to the free alcohol using AcOH/THF/H2O (3:1:1) at room temperature.5

Silylation of Azomethine Anions.

The only other synthetically useful reaction reported for tribenzylchlorosilane involves the C-silylation of azomethine anions. Deprotonation of the parent imine (n-Butyllithium) followed by C-trapping of the resulting azomethine anion affords the a-silylimine in moderate yield (eq 2).6

Related Reagents.

t-Butyldimethylchlorosilane; t-Butyldimethylsilyl Trifluoromethanesulfonate; Chlorotriethylsilane.

1. Jenkins, J. W.; Post, H. W. JOC 1950, 15, 556.
2. Robison, R.; Kipping, F. S. JCS 1908, 439.
3. Martin, G.; Kipping, S. F. JCS 1909, 302.
4. Grant, M. W.; Prince, R. H. JCS(C) 1969, 1138.
5. Corey, E. J.; Ensley, H. E. JOC 1973, 38, 3187.
6. Popowski, E.; Konzempel, K.; Schott, G. ZC 1974, 14, 289.

Paul Sampson

Kent State University, OH, USA

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