Protecting Groups in Organic Chemistry

In a cheap and eco-friendly process, primary and secondary alcohols were easily protected as bis(methoxyphenyl)methyl (BMPM) ethers in good yields using CuBr 2 as a catalyst in acetonitrile at room temperature. Deprotection could easily be achieved using the same catalyst but in ethanol. Both Cu-cat-alyzed protection and deprotection were orthogonal to other methods and fully compatible with other functional groups.

This review considers two aspects of the interaction of Grignards with silanes. First, focusing on technologies that are still viable within the context of current organosilane and silicone technology. Guidelines are provided for silicon-carbon bond formation using Grignard chemistry. Second, the use of silane-blocking agents and their comparative stability in the presence of Grignard reagents employed in organic synthesis is discussed.

The methoxyamine group represents an ideal protecting group for the nitroxide moiety. It can be easily and selectively introduced in high yield (typically >90%) to a range of functionalised nitroxides using FeSO4·7H2O and H2O2 in DMSO. Its removal is readily achieved under mild conditions in high yield (70–90%) using mCPBA in a Cope-type elimination process.

Chromogenic or fluorogenic silanes are formed in which a reactive organosilane is coupled to a chromogenic or fluorogenic nucleus of the coumarin class of compounds, by an ether, urethane or urea linkage. The preferred compounds have the general formula. wherein X is a displaceable or hydrolyzable group which allows the silanes to derivatize protic materials; R' is an aliphatic or aromatic hydrocarbon group; L is an ether (O), urethene (NCO) or urea (NCN) linkage; Cou is a coumarin derivative; n=1 to 8; y=1 to 3 and Z=0 to 2, such that y plus z equal 3. The ether linked silanes may be formed by hydrosilylation of an alkenyl ether of the coumarin compound, while the urethane or urea linked silanes may be formed by the direct reaction of a reactive silylisocyanate with a hydroxyl- or amine-substituted coumarin compound. The silanes are useful in derivatizing protic materials to provide the protic materials with chromogenic or fluorogenic properties.

Attempted detosylation of the 3-amino-1-(p-tosylamino)indole-2-carbonitriles 4a–c using either K2CO3 in EtOH or DBU in PhH at reflux gives unexpectedly the 3-(N-p-tosylamino)indole-2-carbonitriles 5a–c, respectively in high yields. Nevertheless, treatment of 1-(p-tosylamino)indoles 4a–c with thiophenol and DBU in PhH at reflux gives the detosylated 3-aminoindole-2-carbonitriles 5a–c. Reaction mechanisms supporting the tosyl migration (4→5) and the reductive detosylation (4→2) are proposed. All new compounds are fully characterised.

The electrochemical hydrogenolysis of benzyl and carboxybenzyl protecting groups is described. Optimisation of a synthetic protocol afforded well-defined palladium (Pd) nanoparticles on the surface of multiwall carbon nanotubes (CNTs). The high surface area composite was investigated, and differences observed in the voltammetry for the same composite in aqueous and ionic liquid systems are discussed. When used to reduce acidic protons in the ionic liquid (IL) 1-ethy-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C2mim][NTf2]) reactive palladium hydride was formed efficiently, which rapidly performed hydrogenolysis. The compounds 1-(3-(benzyloxy)propyl)-4-methoxybenzene, benzyl octyl carbonate, N,N′-bis(benzyloxycarbonyl)-L-lysine and N-benzyl-L-prolinol were investigated. Extended electrolysis of bis(trifluoromethylsulfonyl)imide (H[NTf2]) in [C2mim][NTf2] containing alcohol groups protected with benzyl and carboxybenzyl groups afforded the alcohol product in high yield. The probable hydrogenolysis of the similarly protected amine groups is also reported.

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Silylation is the replacement of an active hydrogen of a protic material with a substituted silicon atom. Silylation is used to create problems protecting groups in organic synthesis. Trimethylsilylation is the most common example followed by t-butyldimethylsilylation. A description of simple procedures for silylation are presented.

Attempted detosylation of the 3-amino-1-(p-tosylamino)indole-2-carbonitriles 4a–c using either K2CO3 in EtOH or DBU in PhH at reflux gives unexpectedly the 3-(N-p-tosylamino)indole-2-carbonitriles 5a–c, respectively in high yields. Nevertheless, treatment of 1-(p-tosylamino)indoles 4a–c with thiophenol and
DBU in PhH at reflux gives the detosylated 3-aminoindole-2-carbonitriles 5a–c. Reaction mechanisms supporting the tosyl migration (4/5) and the reductive detosylation (4/2) are  proposed. All new compounds are fully characterised.