Categories: O-H Bond Formation >
Cleavage of silyl ethers
Hf(OTf)4 exhibits exceptionally high potency in desilylations. Since the amounts of Hf(OTf)4 required for the deprotection of 1°, 2°, 3° alkyl and aryl tert-butyldimethylsilyl (TBS) ethers range from 0.05 mol% to 3 mol%, a regioselective deprotection can be achieved. A chemoselective cleavage of different silyl ethers or removal of TBS in the presence of most hydroxyl protecting groups was also accomplished.
X.-A. Zheng, R. Kong, H.-S. Huang, J.-Y. Wei, J.-Z. Chen, S.-S. Gong, Q. Sin, Synthesis, 2019, 51, 944-952.
Various tert-butyldimethylsilyl (TBS, TBDMS) ethers as well as tert-butyldiphenylsilyl (TBDPS) ethers can be easily deprotected by employing a catalytic amount of acetyl chloride in dry MeOH in good yields. This mild and convenient method tolerates various other protecting groups and does not lead to acylated or chlorinated byproducts.
A. T. Khan, E. Mondal, Synlett, 2003, 694-698.
Catalytic quantities of fluoride at neutral pH in mixed organic-aqueous solutions that contain buffer cleaved various silicon-oxygen bonds. These conditions show tolerance for acid- and base-sensitive groups. A modified procedure using catalytic fluoride in anhydrous dimethyl sulfoxide-methanol generates primarily volatile silicon byproducts.
A. M. DiLauro, W. Seo, S. T. Phillips, J. Org. Chem., 2011, 76, 7352-7358.
The use of a cyclopropenium cation as a phase-transfer catalyst enables a convenient O-silyl ether deprotection. Mechanistic insight into this deprotection methodology are also provided.
R. Mir, T. Dudding, J. Org. Chem., 2017, 82, 709-714.
A very mild and environmentally benign method for the removal of silyl protecting groups using catalytic amounts of iron in MeOH is particularly effective for cleaving triethylsilyl (TES) groups.
Y.-Q. Yang, J.-R. Cui, L.-G, Zhu, Y.-P. Sun, Y. Wu, Synlett, 2006, 1260-1262.
PMA supported on SiO2 is found to be an efficient catalyst for the chemoselective, mild deprotection of TBDMS ethers. Various labile functional groups such as isopropylidene acetal, OTBDPS, OTHP, Oallyl, OBn, alkene, alkyne, OAc, OBz, N-Boc, N-Cbz, N-Fmoc, mesylate, and azide are tolerated. The supported catalyst and the solvent can be readily recovered and recycled.
G.D. K. Kumar, S. Baskaran, J. Org. Chem., 2005, 70, 4520-4523.
With either 1.0 or 0.10 equivalent of DBU, smooth desilylation of various aryl silyl ethers was accomplished selectively in the presence of base-sensitive groups such esters and alkyl silyl ethers. A direct transformation of aryl silyl ethers into biaryl ethers was possible through tandem desilylation and SNAr reaction with activated aryl fluorides.
C.-E. Yeom, H. W. Kim, S. Y. Lee, B. M. Kim, Synlett, 2007, 146-150.
Chiral diaminodioxaphosphonium salts can be used in catalytic amounts in a highly enantioselective protonation of α-amino acid-derived ketene disilyl acetals in the presence of 2,6-dimethylphenol as stoichiometric proton source.
D. Uraguchi, N. Kinoshita, T. Ooi, J. Am. Chem. Soc., 2010, 132, 12240-12242.