0-Triphenylmethyl derivatives selective triphenylmethylation

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... 

Amines can also be protected from unwanted acylation or from twofold alkylation by alkylation with a sterically demanding group that is amenable to selective removal after completion of the synthesis. The most commonly used groups for this purpose are triphenylmethyl derivatives. Amines are readily tritylated using trityl chloride in the presence of a tertiary amine. Deprotection is achieved by treatment with dilute... 

Pracejus and co-workers also described an alternative method for preparing suitable enolates in situ, Michael addition of a thiol to an acrylate [8]. A selected example of this reaction, for which enantioselectivity is in the range 20-54% ee, is shown in Scheme 9.3, Eq. (a). Use of a catalytic amount (5 mol%) of quinidine, 7, gave the (R)-cysteine derivative 6 with 54% ee. Benzyl thiol, benzhydryl thiol, or triphenylmethyl thiol were used as the thiol component. In addition to acrylates, nitroalkenes were used as a starting material. 

Selectivity data may be also employed to confirm or rule out the existence of a single intermediate in a number of closely related reactions. Thus the ability of the leaving group to influence the selectivity of the competitive attack of water and borohydride in the reaction of a number of diphenylmethyl derivatives testifies to the fact that attack occurs at the ion pair stage and not on the free carbocation (Bell and Brown, 1966). The dependence of the ratio kti/k-w on the leaving group in the solvolysis of a number of triphenylmethyl derivatives leads to the same conclusion regarding the triphenylmethyl system (Hill, 1965). 

Other Alkyl and Aryl Ethers. - The preparation of selectively 0-alkylated saccharides, including benzyl, allyl, triphenylmethyl, and arylalkyl ethers has been reviewed. Analogues of lipids A and X incorporating 3-O-alkyl (rather than acyl) linkages have been described, and some carbohydrate monoalcohol derivatives have been alkylated with haloacetic acid ester derivatives. ° 3-C -Carboxymethyl D-glucose and D-fhictose compounds have been coupled via the carboxylic acid group to L-lysine in a search for acrosin inhibitors."... 

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