Ethers triphenylmethyl

Secondary trityl ethers can best be prepared by reaction with triphenylmethyl perchlorate, but these derivatives tend to be rather labile.2 

Trityl ethers are easily cleaved by mild pro tic acids such as aqueous acetic or trifluoroacetic acid owing to the stability of the triphenylmethyl carbocation. They are also labile in the presence of Lewis acids such as ZnBr2—MeOH, FeCl3 or BF3 Et20.2 Trityl ethers can be cleaved selectively in the presence of TBDMS ether and isopropylidene acetals by brief exposure to formic acid.22 Catalytic hydrogenation has also been used to effect (9-detritylation. 

The introduction and cleavage of the trityl ether proceeds through a very well-stabilised triphenylmethyl carbocation. In the case of trityl ether bond formation, the reaction is performed under anhydrous conditions and the carbocation, which is formed by an SN1 mechanism, reacts with an alcohol. In the case of cleavage, the triphenylmethyl carbocation ion is formed by treatment with acid, which is then trapped by water or a nucleophilic solvent to give trityl alcohol or other derivatives, respectively. Trityl ethers have also been used to protect thiols. 

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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. 

C5H5N CPh3BF4, CH3CN, Pyr, 60-70°, 75-90% yield. Triphenylmethyl ethers can be prepared more readily with triphenylmethylpyridinium fluo-roborate than with triphenylmethyl chloride-pyridine. 

Triphenylmethyl ethers (trityl ethers) have been used to protect primary alcohols selectively [see (14)] , and unhindered secondary alcohols. 

The 21-hydroxyl group in the corticosteroid series can be protected as the base stable triphenylmethyl ether and tetrahydropyranyl ether. " " Mixed acetals from 21-alcohols are extremely acid sensitive compounds. ... 

Benzyl and triphenylmethyl ethers of carbohydrates are preferred over methyl ethers when selective removal of protecting groups is important. The relatively high nucleophilic activity of the 5-hydroxyl group in glycosides and 1,2-O-alkylidene derivatives of 4 permits its benzylation and triphenylmethylation under mild conditions. Thus, treatment of 33 (Ref. 34) and 36 (Ref. 57) with benzyl bromide and... 

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],... 

Fig. 22 Plot of C-OX bond length versus Hammett a for the aromatic substituent Y for triphenylmethyl ethers and esters [108]. The error bars represent two standard deviations in the bond-length measurements. Reprinted with permission from Edwards et al. (1986a). Copyright 1986 American Chemical Society.

G. R. Barker Triphenylmethyl ethers. Methods Carbokydr. Chem. 2 168 (1963). 

To a stirred solution of the (lS,2S,3S)-2-(2,2-dibromovinyl)-3-methyl-l-triphenylmethoxymethyl-cyclopropane (128.6 mg, 0.251 mmol) in THF (5 ml) was added dropwise a 1.42 M solution of nBuLi (0.35 ml, 0.50 mmol) in hexane at -78°C. After stirring at -78°C for 10 min, the solution was poured into H20 (30 ml) and extracted with Et20 (3x30 ml). The organic extracts were combined, washed with brine, dried over sodium sulfate and filtered. The solvent was removed in vacuum to give a colorless residue, which was purified by column chromatography over silica gel (hexane-Et20, 20 1) to afford 81.4 mg (92%) of (lS,2S,3S)-3-ethynyl-2-methylcyclopropylmethyl triphenylmethyl ether as a colorless viscous oil. 

Triphenylmethyl Ethers (Trityl Ethert) and Their Esters... 

Triphenylmethyl ethers, to protect primary alcohols, 19, 60-62, 126, 146, 180 Triphenylmethylsulfenamides, to protect amines, 378... 

All other 17-ester derivatives—4-chlorotestosterone 17-propionate (S-6), 17-succinate, 17-palmitate, 17-enantate, 17-phenylpropionate, 17-triphenylmethyl ether, 17-phenoxyacetate, and 17-cyclopentylpropionate [243] — were reported to be less active than 4-chlorotestosterone acetate. However, 4-chlorotestosterone chloroacetate was reported [263] to be several times more active than 4-chlorotestosterone acetate and 4-chlorotestosterone p-chlorophenoxyacetate was promising in showing a long lasting effect [234,263]. 

Besides the benzyl ethers (Section 2.6.4.1.1.1), which are stable toward normal acidic conditions, acid-labile ethers have been developed. terf-Butyl ethers can be cleaved under conditions used for cleavage of terf-butyl ester and Boc groups, while triphenylmethyl ethers can be cleaved under very mild acidic conditions. 

The triphenylmethyl ethers of the carbohydrates constitute a group of derivatives of particular interest because of the special properties inherent in the trityl group. Before entering into a discussion of these carbohydrate derivatives, a few words regarding the preparation, properties and special behavior of trityl ethers would appear to be in order. 

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