Alessandro Granata

Use of O-thallium(I) salts in the synthesis of phosphate, sulfite, and related ester derivatives of carbohydrates

Abstract O-Thallium(I) salts are shown to promote a variety of rapid, high-yield, substitution reactions at an anomeric, a primary, or a secondary position of carbohydrate derivatives. Syntheses are described of phosphates, phosphites, sulfites, and xanthic ester derivatives. Preparation of the thallous salt involves a facile exchange between thallous ethoxide and an alcohol group of the carbohydrate. The substitution reaction with the appropriate reagent (e.g., a phosphorochloridate) is then conducted in such solvents as benzene or acetonitrile, in which thallous salts are usually soluble. The configuration of an organo-phosphate moiety introduced at the anomeric position is strongly influenced by the choice of solvent, so that a preponderance of either the α- or β-phosphate may be obtained.

Restricted Internal Rotation in 1-Arylhydantoins, 3-Arylhydantoins, and 3-Aryl-2-Thiohydantoins: Reversal of the Effective Sizes of Methyl and Chlorine

In 1-arylhydantoins an o-methyl group is effectively larger than an o-chloro substituent in restricting rotation about the aryl-C—N bond, whereas in 3-arylhydantoins and 3-aryl-2-thiohydantoins the reverse order of sizes is observed. This difference is attributed to repulsion between the chlorine atom and a carbonyl oxygen atom in the torsional transition state of the 3-aryl compounds.