Ethers temporary protection

Reaction sequence E removed an extraneous oxygen by Sml2 reduction and installed an oxygen at C(15) by enolate oxidation. The C(l) and C(15) hydroxy groups were protected as a carbonate in Step E-5. After oxidation of the terminal vinyl group, the C-ring was constructed by a Dieckmann cyclization in Step F-4. After temporary protection of the C(7) hydroxy as the MOP derivative, the (1-ketoestcr was subjected to nucleophilic decarboxylation by phenylthiolate and reprotected as the BOM ether (Steps F-5, F- 6, and F-7). 

A soluble aminomethylated polyethylene glycol and a succinoyl linker were used to support a 9-fluorenylmethyl group for solution-phase glycosylation by the sulfoxide method. With the help of temporary protection by a 6-O-triphenylmethyl ether, the method could be carried out iteratively to form disaccharides (Scheme 4.69) [379],... 

N-alkylation and N-acylation of piperazine-2,5-diones are quite common and have been routinely employed in several synthetic sequences (see Section IV,C). Such operations have also been performed as measures for the temporary protection of the nitrogen during further synthetic maneuvers in other parts of the molecule. Three different alkyl groups have been employed as such protecting groups. Kishi has used the methoxymethyl group for N-protection (potassium r-butoxide, chloro-methyl methyl ether 0°C, 75% yield). Deprotection was achieved by cone. HCl-ethanol at reflux temperature (81T2045). 

The triphenylmethyl (trityl) group remains the most frequently used for the temporary protection of primary hydroxyl groups (for review see Refs. [2, 3, 254]) which can be conveniently regenerated from the corresponding ethers by mild acid treatment or by hydrogenolysis. Moreover, good crystallizing properties of trityl ethers, easy... 

The protecting groups of hydroxy moieties can be classified into three different types, namely alkyl ethers, carbonic acid esters, and sUyl ethers (Scheme 1). Pseudoprolines derived from serine and threonine have also been suggested as a form of temporary protection for both of these amino acids. 

This strategy was followed in the example shown in Scheme 5.5, Scheme 5.6 and Scheme 5.7 using the tert-butyldimethylsilyl ether as the temporary protecting group. Silyl ethers, allyl, p-methoxyphenyl and 2-(trimethylsilyl)ethyl groups are all commonly used for temporary protection of the anomeric position. 

To increase the scope of available hydroxyl protecting groups substituted benzyl ethers, which can be selectively removed in the presence of unsubstituted benzyl ethers have been developed. These substituted benzyl ethers are generally less stable to different reaction conditions than unsubstituted benzyl ethers and therefore are used as temporary protecting groups. 

The triethylsilyl ether 147 thus formed regiospecifically from the diol 150 [Rl=(BnO)2 (0), R2=Bn], which was optically resolved by a chiral column chromatography, was transformed to Ins(2,4,5)P3 and Ins(l,4,5)P3 (Schema 3-23). At this stage, temporary protection of OH-1 with the silyl group is not necessary, i.e. 150 can be directly phosphorylated by the phosphite-phosphonium approach as described in the section on phosphorylation (Scheme 2-6). H The diol 150 was used furthermore as a versatile synthetic intermediate for the synthesis of myo-inositol 1,2-cyclic-4,5-trisphosphate 152 (Scheme 3-23), 8 2-acyl analogues of Ins(1,4,5)P3, and inositol phospholipid. 

Hydroxy protection, the temporary protection of the primary and secondary hydroxy functions of Ser and Thr, respectively, and the aromatic hydroxy group of Tyr in peptide synthesis. The blocking of these functionalities is necessary as they can react with acylating reagents. In SPPS, these amino acids are usually protected as benzyl ethers applying Boc/Bzl tactics or as tert.-butyl ethers in Fmoc/Bu chemistry. 

Prostaglandin endoperoxide. Upjohn chemists have prepared the endoper-oxide PGHs methyl ester (6), from PGFz (1) by conversion to the ditosylate (with temporary protection of the 15-hydroxyl as the t-butyldimethylsilyl ether). 

Transient Protection. Silyl ethers can be used for the transient protection of alcohols (eq 11). In this example the hydroxyl (4) groups were silylated to allow tritylation with concomitant desi-lylation during aqueous workup. The ease of introduction and removal of TMS groups make them well suited for temporary protection. 

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