Silyl Ethers - Thieme Chemistry

Scheme 29 Cleavage of a tert-Butyldimethylsilyl Ether with Hydrogen Fluoride±Pyridine
Complex [63]
PhS
O
TBDMSO
MeO
O
O
SEMO
H
O
O
H
H OMOM
+ diastereomer
58
PhS
O
HF py, py
THF, rt, 2 h
97%
SEMO
O
HO
MeO
O
H
O
O
H
H OMOM
+ diastereomer
rac-[1á(5S*,6S*,8R*,9R*),2á,4aâ,5â,8aá]-6-(Hydroxymethyl)-4-methoxy-9-methyl-2-oxo-8-
[2-(trimethylsilyl)ethoxymethoxy]-1-oxaspiro[4.5]dec-3-en-3-yl 5-(Methoxymethoxy)-1methyl-2-[4-oxo-4-(phenylsulfanyl)butyl]-1,2,4a,5,6,7,8,8a-octahydronaphthalene-1-carboxylate
(59): [63]
To a rapidly stirred soln of the thioester 58 (mixture of 2 diastereomers; 762 mg,
0.83 mmol) in THF (1 mL) was added a HF x ·pyridine soln [5 mL, prepared by diluting Aldrich
HF x ·pyridine (13 g) with pyridine (31 mL) and THF (100 mL)], and the resulting mixture
was stirred at rt for 2 h. After the mixture was poured into sat. NaHCO 3 (50 mL), the
aqueous layer was extracted with Et 2O (3 ” 100 mL) and the combined organic layers were
dried (MgSO 4). After removal of the solvent at reduced pressure, the crude residue was
chromatographed (size C Lobar silica gel column, EtOAc/petroleum ether 28:72) to give
the ªfasterº eluting alcohol 59 as a colorless oil; yield: 289 mg (43%). Further elution afforded
the diastereomeric alcohol as a colorless oil; yield: 360 mg (54%).
4.4.17.3.6.2 Variation 2:
With Mineral Acid
FOR PERSONAL USE ONLY
392 Science of Synthesis 4.4 Silicon Compounds
A solution of a mineral acid such as hydrochloric acid can accomplish selective cleavage
of certain silyl ethers, including tert-butyldimethylsilyl ethers. [64] An illustration of this selectivity
is seen in the reaction of the differentially protected tetrakis(silyl ether) 60 with
10% hydrochloric acid, which leads to the diol 61 (Scheme 30). [65] Only the trimethylsilyl
and tert-butyldimethylsilyl ethers are cleaved under these conditions, the triisopropylsilyl
and tert-butyldiphenylsilyl ethers being unreactive.
White, J. D.; Carter, R. G., SOS, (2002) 4, 371. 2002 Georg Thieme Verlag KG
59