[94124-39-7] · C11H17BrOSi · Bromo(t-butyl)(methoxy)phenylsilane · (MW 273.24)
(reagent for the protection of primary, secondary, and tertiary alcohols; reacts selectively with primary hydroxy groups in dichloromethane; t-butylmethoxyphenylsilyl ethers are highly reactive towards F-, allowing for selective removal in the presence of other silyl protecting groups1)
Alternate Name: bromo-(1,1-dimethylethyl)methoxyphenylsilane.
Physical Data: bp 97-102 °C/1 mmHg; d 1.201 g cm-3; fp 106 °C.
Solubility: sol most organic solvents.
Form Supplied in: clear liquid.
Handling, Storage, and Precautions: corrosive, lachrymator; the reagent is light and moisture sensitive and should be handled under an inert atmosphere. Use in a fume hood.
Bromo(t-butyl)(methoxy)phenylsilane reacts with primary, secondary, and tertiary alcohols in DMF, in the presence of Triethylamine, to give the corresponding silyl ethers in good yield (eqs 1 and 2). Under the same conditions, enolizable ketones may be converted efficiently to silyl enol ethers (eq 3).
In the case of secondary alcohols, silylation can be achieved in dichloromethane in the presence of a small amount of DMF (0.02 equiv). This accelerating effect of DMF has been rationalized based on the involvement of a more reactive hexacoordinated silicon species. Chemoselective silylation of primary alcohols can be achieved when dichloromethane is used as the only solvent (eq 4).1
One of the most striking and useful features of the t-butyl(methoxy)phenylsilyl ether group is its sensitivity to fluoride. Removal of this protecting group can be achieved using Tetra-n-butylammonium Fluoride (1M solution in THF) in dry dichloroethane (10% v/v), in the presence of primary or secondary t-butyldimethylsilyl or t-butyldiphenylsilyl ethers (eqs 5 and 7).1 Selective cleavage of a t-butyldimethylsilyl ether in the presence of a t-butyl(methoxy)phenylsilyl ether is possible under acidic conditions (eqs 6 and 8).
The t-butyl(methoxy)phenylsilyl protecting group is compatible with reactions such as PCC oxidation,2 acylation, tosylation, NaBH4 reduction, benzylation, and hydrogenolysis.
Note that the use of this reagent on chiral molecules will produce diastereoisomers; this may complicate interpretation of NMR spectra.
Yvan Guindon & Christiane Yoakim
Bio-Méga/Boehringer Ingelheim Research, Laval, Quebéc, Canada