- H 2 SO 4
OCH 2. OCH
OCH OCH
H 2 CC(CH 3 ) 2
H 3 O+ +(CH
3 ) 3 COH
4-Pentyn-1-ol
H 2 CH 2 CH 2 Br (CH 3 ) 3 C 2 CH 2 CH 2 BrNaCCH
(CH 3 ) 3 C 2 CH 2 CH 2 C CH H H 2 CH 2 CH 2 C CH
2 O
11.15D SILYL ETHER PROTECTING GROUPS
- A hydroxyl group can also be protected by converting it to a silyl ether group.
- tert-butyldimethylsilyl ether group [tert-butyl(CH 3 ) 2 Si–O–R, or TBDMS–O–R]:
i) Triethylsilyl, triisopropylsilyl, tert-butyldiphenylsilyl, and others can be used.
ii) The tert-butyldimethylsilyl ether is stable over a pH range of roughly 4~12.
iii) The alcohol is allowed to react with tert-butylchlorodimethylylsilane in the
presence of an aromatic amine (a base) such as imidazole or pyridine.
ROH Si
CH 3
CH 3
C(CH) 3 Si
CH 3
CH 3
Cl C(CH) 3
Cl)
DMF
(−H
R O
(TBDMSCl)
(R−O−TBDMS)
+ imidazole
tert-butylchlorodimethylsilane
iv) The TBDMS group can be removed by treatment with fluoride ion
(tetrabutylammonium fluoride):
Bu 4 N+F−
Si THF
CH 3
CH 3
C(CH) 3 Si
CH 3
CH 3
R O C(CH) 3
(R−O−TBDMS)
ROH + F
- Converting an alcohol to a silyl ether makes it much more volatile ⇒ can be
analyzed by gas chromatography.
- Trimethylsilyl ethers are often used for this purpose.
11.16 REACTIONS OF ETHERS
