Protection of hydroxy groups

Protection of hydroxy groups is commonly effected by forming the t-butyl ether by reaction with isobutene in the presence of sulphuric or toluene-ju-sulphonic acid, just like with carboxy groups (Section 7.4). Consequently, both groups may be blocked simultaneously by starting with the free acid. t-Butyl ethers are readily cleaved by trifluoroacetic acid. 

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PROTECTION OF CARBONYL AND HYDROXYL GROUPS / 385 2. Protection of Hydroxy Groups... 

Protection of hydroxy groups as the THP and ferf-butyldimethyl silyl ethers and, conversely, deprotection of these derivatives to the original alcohols. 

Scheme 4.4. Regioseiective protection of hydroxy groups on neamine.

Y. Oikawa, T. Yoshioka, and O. Yonemitsu, Protection of hydroxy groups by intramolecular oxidative formation of methoxybenzylidene acetals with DDQ, Tetrahedron Lett. 889 (1982) Y. Oikawa, T. Nishi, and 0. Yonemitsu, Kinetic acetalatioa for 1,2- and 1,3-diol protection by the reaction of p-methoxyphenylmethyl methyl ether with DDQ, Tetrahedron Lett 4037... 

Transition metal complexes have been widely investigated as catalysts for the synthesis of alkoxysilanes via alcoholysis of hydrosilanes. The system provides a convenient method for the protection of hydroxy groups in organic synthesis and the synthesis of silyl ethers. The general reaction is shown in Eq. (59). 

Tcrt-butyldimethylsilyl ethers have been used extensively for the protection of hydroxy groups. They are more stable to hydrolysis than trimethylsilyl ethers by a rate factor of 104 and they are compatible with a much wider range of reagents used in organic synthesis. 

Si2.3 Examples of protection of hydroxy groups as silyl ethers... 

Among the many protecting groups proposed so far, only a restricted set has found widespread application. Sufficient experimentation means that they can now be regarded as established procedures however, few groups and combinations have been tried and tested for large-scale synthesis. Excellent reviews of the protection of hydroxy groups in peptide synthesis are available.f 1... 

A general survey of the scope of the reaction between alcohols and dihydropyran to form tetrahydropyranyl ethers may be of value in devising syntheses requiring the protecting of hydroxy-groups. The glycosylation of 3/ -hydroxy-steroids by potato-tuber slices has been systematically investigated. 

The Ireland s)mthetic intermediate 176 was deoxygenated by the Barton procedure to provide 194 (O Scheme 22). Stepwise deprotection and protection of hydroxy groups in 194 afforded 195. De-O-tritylation and Swem oxidation of 195 gave the C10-C15 segment 192. As shown in Scheme 22, this aldehyde was transformed into the C10-C20 segment 197. 

Isomerization of allyl ethers. This complex is particularly useful in curhohydratc chemistry for protection of hydroxy groups by the allyl group. After... 

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