[17922-24-6] · C16H19ClOSi · t-Butoxychlorodiphenylsilane · (MW 290.86)
(reagent for the protection of primary, secondary, and tertiary alcohols; reacts selectively with primary hydroxy groups in dichloromethane; t-butoxydiphenylsilyl ethers are highly reactive towards F-, allowing for selective removal1)
Alternate Name: t-butoxydiphenylsilyl chloride.
Physical Data: bp 130-145 °C/0.5 mmHg; d 1.075 g cm-3; fp 56 °C.
Solubility: sol most organic solvents.
Form Supplied in: pale yellow oil; stabilized with calcium carbonate.
Handling, Storage, and Precautions: corrosive; the reagent is moisture sensitive and should be handled under an inert atmosphere.
t-Butoxychlorodiphenylsilane reacts with primary, secondary, and tertiary alcohols in DMF, in the presence of Triethylamine, to give the corresponding silyl ethers in good yield (eq 1).1 Secondary alcohols can also be silylated in dichloromethane; however, small amounts of 4-Dimethylaminopyridine (0.1 equiv) or N,N-Dimethylformamide (0.1 equiv) are required to catalyze the reaction (eq 2). Selective silylation of primary alcohols can be achieved using dichloromethane alone (eq 3).
One of the most interesting attributes of the t-butoxydiphenylsilyl protecting group is its sensitivity to fluoride. A primary t-butoxydiphenylsilyl ether can be cleaved selectively in the presence of a primary or secondary t-butyldimethylsilyl ether, using 2 equiv of Tetra-n-butylammonium Fluoride (1 M solution in THF) in dry dichloromethane (eqs 4, 6, 7).1,2 Alternatively, selective cleavage of the t-butyldimethylsilyl ethers can be achieved using acidic conditions (eq 5).1
Selective cleavage of a secondary t-butoxydiphenylsilyl ether in the presence of a primary t-butyldimethylsilyl ether could not be achieved (eq 8). This problem can be circumvented by the use of the diphenylisopropoxysilyl protecting group (eqs 9 and 10).1,3
The t-butoxydiphenylsilyl protecting group is compatible with reactions such as Pyridinium Chlorochromate oxidation,4 acylation, and reduction. Highly reactive nucleophiles such as n-Butyllithium should, however, be avoided.
Yvan Guindon & Christiane Yoakim
Bio-Méga/Boehringer Ingelheim Research, Laval, Québec, Canada