Silyl Ethers - Thieme Chemistry

Scheme 9 Silylation with Chlorotriethylsilane in the Presence of Imidazole [37]
OH O
PMBO
OMe
N
Me
18
TESCl, imidazole
DMF, rt, 15 h
70%
TESO
O
R R OMe
PMBO S N
Me
(3S)-19
+
89:11
TESO
R R OMe
PMBO R N
Me
(3R)-19
(2R,3S,4R)-N-Methoxy-5-(4-methoxybenzyloxy)-N,2,4-trimethyl-3-(triethylsiloxy)pentanamide
(19): [37]
To a soln of a mixture of alcohol stereoisomers 18 (1.02 g, 3.14 mmol) in DMF (15 mL) were
added imidazole (488 mg, 7.16 mmol) and TESCl (0.9 mL, 5.36 mmol) at rt. After being
stirred for 15 h, the mixture was quenched with H 2O. The organic layer was separated,
washed with 0.5 M aq NaHSO 4, sat. aq NaHCO 3 and brine, dried (Na 2SO 4), and concentrated
to give a residue which was purified by flash chromatography (silica gel, EtOAc/hexane
1:9) to give (3S)-19 as a colorless oil [yield: 855 mg (62%)]along with the 3R-diastereomer
[yield: 106 mg (8%)].
4.4.17.2.1.1 Variation 1:
With Chlorotriethylsilane in Pyridine
Chlorotriethylsilane is more reactive when used with pyridine as the solvent. For example,
a relatively difficult silylation of the hindered alcohol 20 to give triethylsilyl ether 21,
an intermediate in a zaragozic acid synthesis, was carried out with chlorotriethylsilane in
pyridine at room temperature (Scheme 10). [38] The tertiary alcohol in 20 was unaffected
under these conditions.
Scheme 10 Silylation with Chlorotriethylsilane in Pyridine [38]
OHC
HO
O
O
Bu t O 2C
O
CO 2Bu t
CO2Bu t
20
OH
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378 Science of Synthesis 4.4 Silicon Compounds
O
TESCl, py, rt, 22 h
82%
OHC
TESO
O
O
Bu t O2C
CO 2Bu t
CO2Bu t
White, J. D.; Carter, R. G., SOS, (2002) 4, 371. 2002 Georg Thieme Verlag KG
O
21
OH
O
O