Silyl Ethers - Thieme Chemistry

Scheme 13 Cleavage of a Triethylsilyl Ether with Hydrogen Fluoride±Pyridine Complex [41]
O
O
N
O
Bn
O
Ph
O
26
O OTES OTIPS
O
O
N
O
Bn
O
HF•py, py, THF, 0 oC 95%
Ph
O
27
O OH OTIPS
(4R)-4-Benzyl-3-[(2R)-2-{(2S,4S,5R,6S)-6-[(1S,5R,6S,7R,8R)-6-hydroxy-1,5,7-trimethyl-3-methylene-4-oxo-8-(triisopropylsiloxy)nonyl]-5-methyl-2-phenyl-1,3-dioxan-4-yl}-1-oxopropyl]oxazolidin-2-one
(27): [41]
To a soln of 26 (162.5 mg, 0.180 mmol) in THF (5 mL) at 0 8C in a Nalgene bottle was added
ca. 4 mL of a HF·pyridine stock soln [HF·pyridine (2 mL), pyridine (4 mL), and THF (16 mL)].
After 2.5 h, the reaction was quenched by the dropwise addition of sat. aq NaHCO 3
(50 mL), and the resultant mixture was stirred at 08C for 30 min. The mixture was then
partitioned between CH 2Cl 2 (10 mL) and H 2O (10 mL). The aqueous layer was separated
and extracted with CH 2Cl 2 (5 ” 10 mL). The combined organic layers were washed with
1 M aq NaHSO 4, dried (Na 2SO 4), filtered, and concentrated in vacuo. The residue was purified
by flash chromatography (2 ” 13.5 cm silica gel column, linear gradient 10 to 20%
EtOAc/hexanes) to afford 27 as a clear colorless oil; yield: 135.2 mg (95%).
4.4.17.2.3.1 Variation 1:
In the Presence of4-Toluenesulfonic Acid
Highly selective cleavage of triethylsilyl ethers can be realized with the acidic catalyst 4toluenesulfonic
acid in the presence of an alcohol such as methanol. [4] For example, the
triethylsilyl ether 28 undergoes cleavage using these conditions without affecting the
methoxymethyl, tert-butyldimethylsilyl, or 4-methoxybenzyl ethers present in this structure
(Scheme 14). The resultant alcohol 29 is a pivotal intermediate in Marshall s synthesis
of discodermolide. [43]
Scheme 14 Cleavage of Triethylsilyl Ethers Using 4-Toluenesulfonic Acid as a Catalyst [43]
O
OPMB OTBDMS OMOM
O
FOR PERSONAL USE ONLY
4.4.17 Silyl Ethers 381
OMOM
28
OPMB OTBDMS OMOM
OPMB OTES
OMOM
29
OPMB OH
TsOH, MeOH
0 oC, 1 h
72%
for references see p 410
White, J. D.; Carter, R. G., SOS, (2002) 4, 371. 2002 Georg Thieme Verlag KG