Ethers hydroxyl group, protection

Hydroxyl groups protected as acetonides or as silyl, tetrahydropyranyl, benzyl, or methoxymethyl ethers are stable to these conditions. Yields with KMn04 are higher than those obtained with KMn04 and dicyclohexyl- 18-crown-6, Bu4NMn04, or NaMn04H20. ... 

Aldonolactones having their hydroxyl groups protected as ethers (mainly benzylated and silylated derivatives) have been employed for chain elongation through the carbonyl group, and therefore these type of derivatives are included in Section V. 

Ethyl vinyl ether is also useful for hydroxyl-group protection. The resulting derivative (1-ethoxyethyl ether) is abbreviated as the EE group.5 As with the THP group, the EE group contains a stereogenic center. 

Hydroxyl group, protection of, 10-142 as esters, 87-118 Reactivity Chart 2, 417-420 as ethers, 14-87 ... 

The benzyloxycarbonyl group (Cbz or Z) is useful in carbohydrate syuithesis, not only for IV-protection of amino sugars, but also to protect alcohols [262,263]. The main advantage of this group is that it is cleaved by hydrogenolysis, and when compared to benzyl ethers, benzyl carbonates are not only removed more readily [264] but also allow hydroxyl group protection under softer conditions than those employed for benzylation. 

Poly (vinyl alcohol) macromonomers having the hydroxyl groups protected as silyl ethers were prepared using p-formylstyrene as initiator [218] (Scheme 67). 

To this end, the lactone carbonyl was reduced, and the resulting hydroxyl group protected as its silyl ether and reacted with 3,4,5-trimethoxyphenyl magnesium bromide to give the 2,5-frarcs-configurated diarylfuran in large excess over the cw-one. Desilylation of the primary hydroxyl group in the side chain led to MK-0287 34 in 30% overall yield from the precursor of 30 [56]. 

Hydroxyl group protection. Alcohols form ethers with this reagent in the presence of AgOTs and pyridine. The protecting group is stable to acids and bases, and it is removed by Zn-ZnBrj or lithium phthalocyaninatocobaltate. 

Some of the original work in the carbohydrate area in particular reveals extensive protection of carbonyl and hydroxyl groups. For example, a cyclic diacetonide of glucose was selectively cleaved to the monoacetonide. A summary describes the selective protection of primary and secondary hydroxyl groups in a synthesis of gentiobiose, carried out in the 1870s, as triphenylmethyl ethers. 

The tritylone ether is used to protect primary hydroxyl groups in the presence of secondary hydroxyl groups. It is prepared by the reaction of an alcohol with 9-phenyl-9-hydroxyanthrone under acid catalysis (cat. TsOH, benzene, reflux, 55-95% yield).It can be cleaved under the harsh conditions of the WolfT-Kishner reduction (H2NNH2, NaOH, 200°, 88% yield), " and by electrolytic reduction (-1.4 V, LiBr, MeOH, 80-85% yield). It is stable to 10% HCl, 55 h. ... 

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