Silyl Ethers - Thieme Chemistry

4.4.17.5.7.1 Variation 1:
Cleavage with Hydrogen Fluoride±Triethylamine Complex
The use of triethylamine in place of pyridine with hydrogen fluoride renders the fluoride
ion a potent nucleophile while suppressing side reactions that occasionally result from
acid catalysis by hydrogen fluoride±pyridine complex. The hydrogen fluoride±triethylamine
system in acetonitrile as the solvent is particularly useful for cleaving tert-butyldiphenylsilyl
ethers in structures that contain acid-sensitive functional groups. The deprotection
of tert-butyldiphenylsilyl ether 105, which bears numerous appendages that
would be susceptible to acidic hydrolysis, illustrates an application of this reagent
(Scheme 52). The resultant primary alcohol 106 was a key intermediate in a synthesis of
(+)-damavaricin D. [101]
Scheme 52 Cleavage of a tert-Butyldiphenylsilyl Ether with Hydrogen Fluoride±Triethylamine
Complex [101]
MOMO
O
OMOM
O
OMOM
FOR PERSONAL USE ONLY
408 Science of Synthesis 4.4 Silicon Compounds
O
SiMe 3
O OAc OAc O O OTBDPS
O O
105
MOMO
O
Et3N HF, MeCN, reflux, 12 h
89%
OMOM
O
OMOM
O
SiMe3
O OAc OAc O O OH
106
O O
2-(Trimethylsilyl)ethyl 8-Allyloxy-5-[(2E,4S,5S,6R,7R,8R,9R,10R,11R,12R)-5,7-diacetoxy-8-
(allylcarbonyloxy)-13-hydroxy-9,11-(isopropylidenedioxy)-2,4,6,10,12-pentamethyl-1-oxotridec-2-enyl]-1,4,6-tris(methoxymethoxy)-3,7-dimethylnaphthalene-2-carboxylate
(106): [101]
A soln of silyl ether 105 (0.70 g, 0.53 mmol) and Et 3N·HF (250 mg, 2.1 mmol) in MeCN
(6.0 mL) was heated at reflux for 12 h. The soln was allowed to cool to 238C then partitioned
between Et 2O (400 mL) and H 2O (150 mL). The organic phase was washed with
NaHCO 3 soln (50 mL) and H 2O (50 mL), dried (MgSO 4), filtered, and concentrated, which
afforded a yellow oil. Purification of the crude product by flash chromatography
(EtOAc/hexanes 3:7) gave the alcohol 106 as a ca. 1:1 mixture of atropisomers (white
foam); yield: 0.51 g (89%).
White, J. D.; Carter, R. G., SOS, (2002) 4, 371. 2002 Georg Thieme Verlag KG