Tritylon group

The tritylone group (22), which has been used199 for the protection of alcohols, resembles the trityl group, but it is more stable to acid. It... 

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. ... 

Tritylone ethers (57), used as acid-stable protecting groups for alcohols, are cleaved under Wolff-Kishner (Huang-Minlon) conditions as the unblocking step. ... 

Carbinols conjugated with aromatic systems, such as benzylic alcohols [59-62], trityl (VIII), tritylone (IX), and benzhydryl alcohols [59,62,63], and 9-hydroxy-9-phenylan-throne, heteroaromatic systems [64], a-hydroxy ketones [65-67], a-hydroxy acids, and their derivatives [68-70] can also be cleaved at potentials less negative than that of the activating group. Thus the radical anion of benzyl benzoate cleaves rapidly to benzoate and benzyl radical, which is reduced to the anion protonation leads to toluene. In the absence of added proton donor, the base generated during the reduction (EGB) may cleave the ester to benzoate and benzyl alcohol [44]. 

The suitability of tritylone ethers as protecting groups for alcohols has been explored, with cholesterol among model alcohols.The ether (134) was formed from tritylone alcohol and cholesterol under acidic conditions with azeotropic... 

The selective blocking of primary or secondary hydroxy-groups with electroactive protecting groups reduced at different potentials is illustrated in Scheme 38 with tritylone (c/. 4,155) and 4-cyanobenzyl ethers, removed at -1.4 and -2.2 volts, respectively (relative to an Ag/AgCl electrode). ... 

The utility of but-2-enyl ethers as alcohol protecting groups has been described the function is stable to mild acid and base, but is readily cleaved by potassium t-butoxide in DMSO at room temperature. A full description of the use of tritylone ethers as protecting groups has been published. 

An alcohol protecting group cleavable by specific base catalysis is offered as an alternative to the more common acid-labile functions. Tritylone ethers... 

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