Silyl Ethers - Thieme Chemistry

Scheme 47 Cleavage of a Bis(tert-butyldiphenylsilyl ether) with Tetrabutylammonium
Fluoride [94]
TBDPSO
O
OTBDPS
O O
95
HO
3
O
OH
O O
96
TBAF, THF
0 oC to rt, 12 h
83%
A tert-butyldiphenylsilyl ether is more susceptible to attack by fluoride ion than a triisopropylsilyl
ether, a property that can be attributed to electron withdrawal by the phenyl
substituents on silicon. This distinction is manifested, for example, in the selective cleavage
of the tert-butyldiphenylsilyl ether of 97, yielding alcohol 98 in which the triisopropylsilyl
ether is left intact (Scheme 48). [65]
Scheme 48 Cleavage of a tert-Butyldiphenylsilyl Ether with Tetrabutylammonium
Fluoride [65]
TIPSO
O
CO2H
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4.4.17 Silyl Ethers 405
TBDPSO
97
O
O
Pr i
TIPSO
TBAF, THF
rt, 4 d
68%
(+)-Isobretonin A (96): [94]
To a soln of bis(silyl ether) 95 (190 mg, 0.2 mmol) in THF (20 mL) at 08C under argon was
added 1 M TBAF in THF (0.5 mL, 0.5 mmol). The mixture was allowed to reach rt and was
stirred for 12 h. The reaction was then quenched with silica gel (2 g) and the soln was concentrated.
The mixture was dissolved in CH 2Cl 2 (1 mL) and purified by column chromatography
(silica gel, EtOAc/hexane 1:3) to give isobretonin A (96); yield: 68.38 mg (83%).
(3Z,3aR,4R,6S,7S,7aS)-3-{(2E,4R,6E)-8-[(2R,4S,8R,9S)-4-Hydroxy-8-isopropyl-9-methyl-1,7dioxaspiro[5.5]undec-2-yl]-4,6-dimethylocta-2,6-dienylidene}-6-methyl-7-(triisopropylsiloxy)octahydrobenzofuran-4-carboxylic
Acid (98): [65]
1 M TBAF in THF (0.24 mL, 0.24 mmol) was added to a soln of acid 97 (0.24 g, 0.25 mmol) in
THF (5.0 mL). The resulting soln was stirred for 3 d at rt, and more TBAF soln (0.12 mL,
0.12 mmol) was added. Following an additional 1 d of stirring, the soln was concentrated
O
CO 2H
98
HO
O
O
3
Pr i
for references see p 410
White, J. D.; Carter, R. G., SOS, (2002) 4, 371. 2002 Georg Thieme Verlag KG