Friedel–Crafts catalysts as assistants in the tritylation of less reactive hydroxyls

Abstract

Less reactive hydroxyls, such as those present in secondary alcohols and in some primary alcohols, phenols and carboxylic acids, were easily tritylated with the homogeneous assistance of equimolar quantities of chlorides of di- and trivalent metals in aprotic solvents. The metal ions allowed both high concentration of the effective reagent triphenylmethylcarbenium ion and mobilisation of the hydroxyl proton, thus giving rise to rapid, room temperature substitution reactions. The experimental conditions were so mild that other protected groups, such as alkyl- or trityl-protected carboxyls and (9-fluorenylmethoxycarbonyl)- or trityl-protected amino groups, remained unaffected.