Hydroxyl groups, tritylation

As previously discussed, ethyl chlorocarbonate reacts rapidly and selectively with an equatorial 3-hydroxyl group to give the corresponding cathylate. Trityl ethers, usually employed as a selective protecting group for primary hydroxyls, can be prepared from A -3j3-ols by heating with triphenylmethyl chloride in pyridine, and from 5a-3 -alcohols by more prolonged heat-... 

The first objective was the conversion of L-tryptophan into a derivative that could be converted to pyrroloindoline 3, possessing a cis ring fusion and a syn relationship of the carboxyl and hydroxyl groups. This was achieved by the conversions shown in Scheme 1. A critical step was e. Of many variants tried, the use of the trityl group on the NH2 of tryptophan and the t-butyl group on the carboxyl resulted in stereospecific oxidative cyclization to afford 3 of the desired cis-syn stereochemistry in good yield. 

The two primary hydroxyl groups in maltose and its derivatives show a large difference in reactivity. On selective tritylation, /3-maltose,238 benzyl /3-maltoside,239 and methyl 3-0-(methylsulfonyl)-/3-maltoside127 all gave mainly 6 -0-trityl compounds. Tritylation of cyclohexaamylose130 and amylose132,240 yielded the expected 6-0-trityl derivatives. 

Micheel then slightly modified his synthesis, starting from D-galactose diethyl dithioacetal (19) (Scheme 2).33 Selective tritylation of the 6-hydroxyl group followed... 

Trityl chloride reacts more readily with primary than with secondary hydroxyl groups, so that it is possible to isolate 1,6-ditrityl ethers. ... 

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