Silyl Ethers - Thieme Chemistry

Scheme 50 Selective Cleavage of a tert-Butyldiphenylsilyl Ether with Tris(dimethylamino)sulfur
(Trimethylsilyl)difluoride [97]
TBDMSO
TBDPSO
101
O
O
O
Bu t
TASF (1.2 equiv)
DMF, 0 oC to rt
84%
TBDMSO
(2R,5S,6S,9R)-2-tert-Butyl-6-[(1E,3S)-3-(tert-butyldimethylsiloxy)-2-methylhexa-1,5-dienyl]-
8-(hydroxymethyl)-9-methyl-1,3-dioxaspiro[4.5]dec-7-en-4-one (102): [97]
To a 08C soln of bis(silyl ether) 101 (57 mg, 0.080 mmol) in DMF (0.500 mL) was added
1.30 M TASF in DMF (0.073 mL, 0.095 mmol). The reaction was stirred at 0 8C for 2 h, then
warmed to rt for 2 h. The mixture was diluted with EtOAc and washed with pH 7 buffer.
The aqueous layer was extracted with EtOAc (3 ” 10 mL) and the combined organic layers
were dried (MgSO 4), filtered and concentrated in vacuo. The crude oil was purified by
chromatography (silica gel, Et 2O/hexanes 1:1) to give 102; yield: 32 mg (84%).
4.4.17.5.7 Method 7:
Cleavage of tert-Butyldiphenylsilyl Ethers with
Hydrogen Fluoride±Pyridine Complex
Hydrogen fluoride±pyridine complex in tetrahydrofuran [98] and hydrogen fluoride in
aqueous acetonitrile [99] are effective reagents for unmasking a tert-butyldiphenylsilyl
ether. They are relatively unselective but are valuable for cleaving a tert-butyldiphenylsilyl
ether where basic conditions (e.g., see Section 4.4.17.5.5) cannot be employed. An application
of the hydrogen fluoride±pyridine reagent is seen in the deprotection of the tertbutyldiphenylsilyl
ether 103 to give alcohol 104 (Scheme 51), an intermediate in a route
to (+)-acetoxycrenulide. [100]
Scheme 51 Cleavage of a tert-Butyldiphenylsilyl Ether with Hydrogen
Fluoride±Pyridine Complex [100]
TBDPSO
O
O H H
103
FOR PERSONAL USE ONLY
4.4.17 Silyl Ethers 407
HF py
MeCN, H2O, 6 h
85%
HO
O
104
102
O
HO
O H H
H OAc
H OAc
(4S,5R,7R,7aS,8aS)-5-Acetoxy-4-[(1R)-4-hydroxy-1-methylbutyl]-7-methyl-3,4,5,6,7,7a,8,8aoctahydro-1H-cyclopropa[3,4]cycloocta[1,2-c]furan-1-one
(104): [100]
A soln of silyl ether 103 (153 mg, 0.27 mmol) in MeCN (8 mL) was treated with HF·py soln
[prepared by adding 48% HF (1 mL) to a mixture of MeCN (1 mL) and pyridine (2.4 mL) at
08C]in three equal aliquots (0.33 mL each) over 6 h. The mixture was then diluted with
H 2O and extracted with EtOAc. The combined organic extracts were washed with 5%
HCl, sat. NaHCO 3 soln, and brine prior to drying and solvent evaporation. Chromatography
of the residual gel (EtOAc/hexanes 9:1) afforded alcohol 104 as a colorless oil; yield:
77 mg (85%).
O
O
Bu t
for references see p 410
White, J. D.; Carter, R. G., SOS, (2002) 4, 371. 2002 Georg Thieme Verlag KG