Selective cleavage groups

Selective cleavage of a primary TBDMS group was achieved with acid in the presence of a secondary TBDMS group. 

Selective cleavage of an aiyl methylenedioxy group, or an aryl methyl ether, by boron trichloride has been investigated. 

AcOH, H2O, THF (3 1 1), 25-80°, 15 min to 5 h2 Selective cleavage of a primary TBDMS group was achieved with acetic acid in the presence of a secondary TBDMS group. 

Sodium ethanethiolate has been examined for the selective cleavage of aryl methyl ethers. Methyl ethers para to an electron-withdrawing group are cleaved preferentially. ... 

Selective cleavage of the DMTr group from oxygen is accomplished with 80% aq. AcOH (rt, 10 min), whereas selective cleavage of the DMTr group from the thiol is effected with AgN03/NaOAc buffer (rt, 1 min). ... 

Acidic ether cleavages are typical nucleophilic substitution reactions, either SN1 or Sn2 depending on the structure of the substrate. Ethers with only primary and secondary alkyl groups react by an S 2 mechanism, in which or Br attacks the protonated ether at the less hindered site. This usually results in a selective cleavage into a single alcohol and a single alkyl halide. For example, ethyl isopropyl ether yields exclusively isopropyl alcohol and iodoethane on cleavage by HI because nucleophilic attack by iodide ion occurs at the less hindered primary site rather than at the more hindered secondary site. 

In order to explain the selective cleavage of the C O bond, one has to take into account two factors (i) the oxonium is a better leaving group than the sulfonium (ii) for a nucleophilic substitution, weak bases are better leaving groups. The proposed mechanism follows Scheme XXI [99, 104] ... 

The electrochemical behaviour of silyl-substituted nitrogen compounds is also interesting. The introduction of a silyl group at the carbon adjacent to the nitrogen of carbamates causes a significant decrease in the oxidation potentials, although such effect is much smaller for amines. Preparative electrochemical oxidation of silyl-substituted carbamates in methanol results in smooth and selective cleavage of the C Si bond and introduction of methanol at the a-... 

Homoallyl ethers or sulfides.1 gem-Methoxy(phenylthio)alkanes (2), prepared by reaction of 1 with alkyl halides, react with allyltributyltin compounds in the presence of a Lewis acid to form either homoallyl methyl ethers or homoallyl phenyl sulfides. Use of BF3 etherate results in selective cleavage of the phenylthio group to provide homoallyl ethers, whereas TiCl effects cleavage of the methoxy group with formation of homoallyl sulfides. 

O Dangles, F Guibe, G Balavoine, S Lavielle. A Marquet. Selective cleavage of the allyl and allyloxycarbonyl groups through palladium-catalyzed hydrostannolysis with tributyltin hydride. Application of the selective protection-deprotection of amino acid derivatives and in peptide synthesis. J Org Chem 52, 4984, 1987. 

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