Categories: O-H Bond Formation >
Cleavage of ethers
An oxidative deprotection of p-methoxy benzyl (PMB) ethers was achieved using a nitroxyl radical catalyst with electron-withdrawing ester groups adjacent to the nitroxyl group in the presence of 1 equiv of PIFA as co-oxidant. The corresponding carbonyl compounds were obtained in the presence of an excess of PIFA.
S. Hamada, K. Sugimoto, E. E. Elboray, T. Kawabata, T. Furuta, Org. Lett., 2020, 22, 5486-5490.
Primary alcohols and ethers were effectively reduced to the corresponding hydrocarbons by HSiEt3 in the presence of catalytic amounts of B(C6F5)3. Secondary alkyl ethers are cleaved under similar reaction conditions to produce silyl ethers or alcohols upon subsequent deprotection with TBAF. The following relative reactivity order of substrates was found: primary >> secondary > tertiary.
V. Gevorgyan, M. Rubin, S. Benson, J.-X. Liu, Y. Yamamoto, J. Org. Chem., 2000, 65, 6179-6168.
A new reagent for the deprotection of various aromatic methyl ethers, 2-(diethylamino)ethanethiol, affords the corresponding phenols in good to excellent yields. Both the reagent and the byproduct 2-(diethylamino)ethyl methyl sulfide are soluble in dilute acid, which allows an essentially odorless workup.
J. Magano, M. H. Chen, J. D. Clark, T. Nussbaumer, J. Org. Chem., 2006, 71, 7103-7105.
In bromination of alkenes by dibromine and dealkylation of aromatic ethers by boron tribromide, a fluorous phase acts as a liquid membrane permitting passive transport of the reagents at the bottom to the top layer involving the substrates, thereby regulating the reactions.
I. Ryu, H. Matsubara, S. Yasuda, H. Nakamura, D. P. Curran, J. Am. Chem. Soc., 2002, 124, 12946-12947.
The ionic liquid [bmim][Br] confers high nucleophilicity on the bromide ion for the nucleophilic displacement of an alkyl group to regenerate a phenol from the corresponding aryl alkyl ether in good yield in the presence of p-toluenesulfonic acid. Dealkylation of various aryl alkyl ethers could also be achieved using stoichiometric amounts of concentrated hydrobromic acid in [bmim][BF4].
S. K. Boovanahalli, D. W. Kim, D. Y. Chi, J. Org. Chem., 2004, 69, 3340-3344.
A tethered alkene functionality can be used as a traceless directing group for a zirconium catalyzed reductive cleavage of Csp3 and Csp2 carbon-heteroatom bonds, including C-O, C-N, and C-S bonds. The reaction is especially useful for cleavage of homoallylic ethers and the removal of terminal allyl and propargyl groups.
C. Matt, F. Kölblin, J. Streuff, Org. Lett., 2019, 21, 6909-6913.
A readily available magnesium catalyst achieves a selective hydroboration of a wide range of epoxides and oxetanes yielding secondary and tertiary alcohols in excellent yields and regioselectivities.
M. Magre, E. Paffenholz, B. Maity, L. Cavallo, M. Rueping, J. Am. Chem. Soc., 2020, 142, 14286-14294.
The homoallyl moiety (hAllyl) can be used as a general protecting group for several functionalities. It can be chemoselectively removed via a sequential, one-pot cross-metathesis/elimination sequence.
B. H. Lipshutz, S. Ghorai, W. W. Y. Leong, J. Org. Chem., 2009, 74, 2854-2857.
Pd(0)-catalyzed deprotection of allyl ethers using barbituric acid derivatives in protic polar solvent such as MeOH and aqueous 1,4-dioxane proceeds at room temperature without affecting a wide variety of functional groups. Control of the reaction temperature allows selective and successive cleavage of allyl, methallyl, and prenyl ethers.
H. Tsukamoto, T. Suzuki, Y. Kondo, Synlett, 2007, 3131-3132.
Allyl aryl ethers can be easily cleaved by the use of 10% Pd/C under mild and basic conditions. The present reaction would involve a SET process rather than a π-allyl-palladium complex. The scope and limitation of this new deprotective methodology are also described.
M. Ishizaki, M. Yamada, S.-I. Watanabe, O. Hoshino, K. Nishitani, M. Hayashida, A. Tanaka, H. Hara, Tetrahedron, 2004, 60, 7973-7981.
Treatment of a various aryl methyl ethers with a mixture of phosphorus pentoxide in methanesulfonic acid enables a simple and efficient one-pot demethylation-mesylation reaction to afford the corresponding aryl mesylates in good yields.
B. Kaboudin, Y. Abedi, Synthesis, 2009, 2025-2028.