Silyl Ethers - Thieme Chemistry

trated in the conversion of 74 into diol 75 (Scheme 37), a late intermediate in a synthesis
of milbemycin D. [65]
Scheme 37 Cleavage of a Triisopropylsilyl Ether with Tetrabutylammonium Fluoride [65]
TIPSO
O
OH
O
FOR PERSONAL USE ONLY
398 Science of Synthesis 4.4 Silicon Compounds
74
O
O
O
Pr i
HO
O
TBAF
THF, rt
95%
(4S,6R,25R)-25-Isopropyl-5-O-demethyl-28-deoxy-3,4-dihydro-6,28-epoxymilbemycin B
(75): [65]
1 M TBAF in THF (0.23 mL, 0.23 mmol) was added to a soln of macrolactone 74 (0.054 g,
0.075 mmol) in THF (1.0 mL). The resulting soln was stirred overnight at rt, concentrated
in vacuo, and purified by column chromatography (silica gel, 10±50% EtOAc/hexanes) to
afford diol 75 as a white foam; yield: 0.040 g (95%).
4.4.17.4.3 Method 3:
Cleavage ofTriisopropylsilyl Ethers with Tris(dimethylamino)sulfur
(Trimethylsilyl)difluoride
Tris(dimethylamino)sulfur (trimethylsilyl)difluoride (TASF) as a source of fluoride ion has
been used to cleave triisopropylsilyl ethers in situations where the basicity of tetrabutylammonium
fluoride would be destructive toward other functionality. An example in
which only tris(dimethylamino)sulfur (trimethylsilyl)difluoride could be employed to
successfully cleave a triisopropylsilyl ether is seen in the conversion of 76 into baccatin
III (78, Scheme 38). [81] Cleavage of the silyl ether to yield alcohol 77 was followed by treatment
with phenyllithium, which removed the 2,2,2-trichloroethoxycarbonyl (Troc) protection
and opened the cyclic carbonate en route to triol 78 (accompanied by a 46% yield
of 10-O-deacetylbaccatin III).
White, J. D.; Carter, R. G., SOS, (2002) 4, 371. 2002 Georg Thieme Verlag KG
OH
O
75
O
O
O
Pr i