Deprotection strategies

Scheme 13.16. Protection-deprotection strategy in microwave-enhanced fluoro-debromination reaction.

We have demonstrated an orthogonal protection/deprotection strategy for preparing a carbohydrate core that could be iteratively deprotected and glycosylated to form... 

Scheme 11.9 Orthogonal deprotection strategy for the preparation of carbohydrate cores.

Scheme 11.10 Application of an orthogonal protection/deprotection strategy in preparation of a tetrasaccharide.

Selective reaction at only one position in a molecule that contains two or more of the same functionality, or different functionalities that react in a similar manner, can be difficult to achieve chemically without lengthy protection/deprotection strategies. In contrast, such regio- and chemo-selective transformations can frequently be realized surprisingly easily with a biocatalyst, as demonstrated by the following examples. 

The preparation of polymer-supported iridium catalysts (61) and (62) for the stereoselective isomerization of double bonds using polystyrene based immobilized triphenyl phosphine were recently reported by Ley and coworkers (Fig. 4.5). The immobilized catalyst is potentially useful for deprotection strategies of aUyl ethers [130]. 

Reduce derivatives - Unnecessary derivatization (blocking groups, protection/deprotection strategies, temporary modification of physical/chemical processes) should be avoided whenever possible. 

Methoxyphenyl ethers can be cleaved by mild oxidants (Entry 10, Table 7.8). Because many acid-labile linkers are also readily oxidized, care must be taken when applying this deprotection strategy. Benzyl ethers have been removed from Tentagel-or PEGA-bound carbohydrates by catalytic hydrogenation using palladium nanoparticles [112],... 

Electroenzymatic reactions are not only important in the development of ampero-metric biosensors. They can also be very valuable for organic synthesis. The enantio- and diasteroselectivity of the redox enzymes can be used effectively for the synthesis of enantiomerically pure compounds, as, for example, in the enantioselective reduction of prochiral carbonyl compounds, or in the enantio-selective, distereoselective, or enantiomer differentiating oxidation of chiral, achiral, or mes< -polyols. The introduction of hydroxy groups into aliphatic and aromatic compounds can be just as interesting. In addition, the regioselectivity of the oxidation of a certain hydroxy function in a polyol by an enzymatic oxidation can be extremely valuable, thus avoiding a sometimes complicated protection-deprotection strategy. 

Selective substitution by different urea groups is easily accomplished using protection-deprotection strategies. Mono-, 1,2-di-, and tri-Boc derivatives are available in gram quantities [30], which allows the preparation of AAAB- and AABB-type... 

Use protection/deprotection strategies to ensure that Bj reacts with all reactive sites of ( ), but that no reactions occur at the new reactive sites on Bx of dendrimer D0. 

A big improvement has been made in synthesis of cyclen. For a long time, the amine has been available mostly through classical so-called tosylamide synthesis <1974JA2268>. The method is atom noneffective , as most of molecular mass disappears by removal of the sulfonate group. Furthermore, harsh deprotection conditions can interfere with numerous functional groups. The method is time consuming when the protection-deprotection strategy is used. 

The three classes of relay deprotection strategies cited above are the most common but there are many other possibilities as in the rhodium(l)-catalysed isomerisation of a robust ally] ether to a hydrolytically labile enol ether discussed in section 1.2.11. 

For the preparation of the required 1 2 [Ru ligand 47] intermediate, a pro-tection-deprotection strategy was employed. This involved reaction of 47 with trimethyloxonium tetrafluoroborate to block one metal co-ordination site in 47 to yield 48. After co-ordination of one ruthenium ion, the remaining site was unblocked by reaction with DABCO in refluxing acetonitrile. Reaction of this 1 2 (metal ligand) product with a second metal ion was then carried out. 

Other / -hydroxybenzyl-derived protecting groups include / -acetoxybenzyl ether and 2-(tri-methylsilyl)ethoxymethoxybenzyl ether [62]. These groups require a two-stage deprotection strategy in which treatment with base or fluoride was followed by thermolysis or mild oxidation of the obtained /7-phenoxybenzyl intermediate ( Scheme 8). The conditions are compatible with many of the standard manipulations of oligosaccharide synthesis and with the presence of benzyl or PMB ethers. 

The application of functionally substituted organozincs allows for the construction of carbon-carbon bonds while circumventing tedious protection-deprotection strategies, as exemplified below.Note that tosyl cyanide reacts with alkenyl or arylzinc reagents to provide a,(3-unsaturated alkenyl or aromatic nitriles, respectively. 

While all known examples of 1,3-diethers with an anti-orientation were obtained via protection/deprotection strategies , the acylation with excess benzoyl chloride using NaH as base was reported to give the anti-isomer in boiling toluene, while the iyn-isomer is formed in THF at 0... 

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