Silyl Ethers - Thieme Chemistry

Scheme 38 Cleavage of a Triisopropylsilyl Ether with Tris(dimethylamino)sulfur (Trimethylsilyl)difluoride
[81]
AcO O OTroc
TIPSO H
O O OAc
O
76
FOR PERSONAL USE ONLY
4.4.17 Silyl Ethers 399
O
TASF, THF, 0 oC, 5 min
96%
PhLi, THF
33%
AcO O OTroc
HO H
O O OAc
O
77
O
AcO O OH
10
HO H O
HO BzO
78
OAc
[3aS-(3aá,5â,8á,9aá,10á,11aâ,13aâ,13bâ,13cá)]-8,13a-Diacetoxy-5-hydroxy-3a,7-methano-6,9a,14,14-tetramethyl-2,9-dioxo-4,5,8,9,9a,10,11,11a,13,13a,13b,13c-dodecahydro-
3aH-oxeto[2¢¢,3¢¢:5¢,6¢]benzo[1¢,2¢:3,4]cyclodeca[1,2-d]-1,3-dioxol-10-yl 2,2,2-Trichloroethyl
Carbonate (77): [81]
To silyl ether 76 (3.2 mg, 4 ìmol) in THF (0.8 mL) at 08C was added TASF (4.0 mg, 15 ìmol),
and the mixture was stirred for 5 min at 0 8C. The reaction was quenched by addition of
sat. aq NaHCO 3. The aqueous layer was extracted with Et 2O. The combined organic layers
were washed with H 2O and sat. brine, and then dried (anhyd Na 2SO 4). The crude mixture
was filtered and concentrated under reduced pressure. Purification of the resultant residue
by flash chromatography (silica gel, EtOAc/hexanes 3:7) provided alcohol 77; yield:
2.5 mg (96%).
4.4.17.4.4 Method 4:
Cleavage ofTriisopropylsilyl Ethers with
Hydrogen Fluoride±Pyridine Complex
Hydrogen fluoride±pyridine complex, used in a mixed tetrahydrofuran/pyridine solvent
system, affords a convenient method for removing the triisopropylsilyl residue from oxygen.
The final step in a synthesis of the immunosuppressant rapamycin (80) involved unmasking
of both a triisopropylsilyl and a tert-butyldimethylsilyl ether, for which hydrogen
fluoride±pyridine complex treatment of 79 served well (Scheme 39). [82]
for references see p 410
White, J. D.; Carter, R. G., SOS, (2002) 4, 371. 2002 Georg Thieme Verlag KG