Acetonides
T. W. Green, P. G. M. Wuts,
Protective Groups in Organic
Synthesis,
Wiley-Interscience, New York, 1999, 207-215, 716-719.
Stability
H2O: | pH < 1, 100°C | pH = 1, RT | pH = 4, RT | pH = 9, RT | pH = 12, RT | pH > 12, 100°C |
Bases: | LDA | NEt3, Py | t-BuOK | Others: | DCC | SOCl2 |
Nucleophiles: | RLi | RMgX | RCuLi | Enolates | NH3, RNH2 | NaOCH3 |
Electrophiles: | RCOCl | RCHO | CH3I | Others: | :CCl2 | Bu3SnH |
Reduction: | H2 / Ni | H2 / Rh | Zn / HCl | Na / NH3 | LiAlH4 | NaBH4 |
Oxidation: | KMnO4 | OsO4 | CrO3 / Py | RCOOOH | I2, Br2, Cl2 | MnO2 / CH2Cl2 |
Protection
ZrCl4 was an efficient catalyst for the deprotection of
1,3-dioxalanes, bis-TBDMS ethers, and diacetate functional groups in excellent
yields. ZrCl4 also promoted diol protection as the acetonide in very
good yields and acted as a transesterification catalyst for a range of
esters.
S. Singh, C. D. Duffy, S. T. A. Shah, P. J. Guiry, J. Org. Chem., 2008,
73, 6429-6432.
Molecular iodine catalyzes acetalation and acetylation of sugars with stoichiometric amounts of enol acetates under solvent-free
conditions to give orthogonally
protected sugar derivatives in short time and good yields. At lower
temperature, it is possible to obtain the acetonide acetate as a single product
whereas peracetate is the major product at higher temperature.
D. Mukherjee, B. A. Shah, P. Gupta, S. C. Taneja, J. Org. Chem., 2007,
72, 8965-8969.
Other Syntheses of Acetonides
Transformation of epoxides to β-alkoxy alcohols, acetonides, and α-alkoxy
ketones is achieved by using molybdenum(VI) dichloride dioxide (MoO2Cl2)
as a catalyst. Alcohol, aldehyde, oxime, tosyl, and tert-butyldimethylsilyl
functional groups are tolerated during the methanolysis and acetonidation of the
functionalized epoxides.
K. Jeyakumar, D. K. Chand, Synthesis, 2008,
807-819.
Deprotection
Deprotection of acetals and ketals can be achieved by using a catalytic
amount of sodium tetrakis(3,5-trifluoromethylphenyl)borate (NaBArF4)
in water at 30 °C. For example, a quantitative conversion of
2-phenyl-1,3-dioxolane into benzaldehyde was accomplished within five minutes.
C.-C. Chang, B.-S. Liao, S.-T. Liu, Synlett, 2007, 283-287.
ZrCl4 was an efficient catalyst for the deprotection of
1,3-dioxalanes, bis-TBDMS ethers, and diacetate functional groups in excellent
yields. ZrCl4 also promoted diol protection as the acetonide in very
good yields and acted as a transesterification catalyst for a range of
esters.
S. Singh, C. D. Duffy, S. T. A. Shah, P. J. Guiry, J. Org. Chem., 2008,
73, 6429-6432.
Aqueous tert-butyl hydroperoxide (70%) is an inexpensive reagent for the
regioselective and chemoselective deprotection of terminal acetonide groups.
Various acetonide derivatives furnish the corresponding deprotected diols in
good yields, while a large number of acid labile protecting functional groups
and other functional moieties were found to be unaffected under the conditions.
M. R. Maddani, K. R. Prabhu, Synlett, 2011,
821-825.
Asymmetric Synthesis of 1-(2- and 3-Haloalkyl)azetidin-2-ones as Precursors
for Novel Piperazine, Morpholine, and 1,4-Diazepane Annulated Beta-Lactams
W. Van Brabandt, M. Vanwalleghem, M. D'hooghe, N. De Kimpe, J. Org. Chem., 2006,
71, 7083-7086.
Indium trichloride in an acetonitrile-water mixture chemoselectively cleaved the
isopropylidene acetals of various 1,3-dioxolanyl-substituted 1,2-oxazines as
well as carbohydrate derivatives. Enol ethers, glycosidic linkages and
acid-sensitive protecting groups such as tert-butyldimethylsilyl,
2-(trimethylsilyl)ethyl, or tert-butoxycarbonyl are not attacked.
F. Pfrengle, V. Dekaris, L. Schefzig, R. Zimmer, H.-U. Reissig, Synlett, 2008,
2965-2968.
Conversion of Acetonides
Treatment of 1,2-O-isopropylidenefuranose derivatives with
triethylsilane/boron trifluoride etherate provides tetrahydrofurans. The removal
of the 1,2-O-isopropylidene group is accompanied by deoxygenation at the
anomeric position. This process is compatible with several hydroxyl protecting
groups.
G. J. Ewing, M. J. Robins,
Org. Lett., 1999, 1, 635-636.