Aldol Reactions of Conformationally Stable Axially Chiral Thiohydantoin Derivatives.

Two novel axially chiral -trifluoromethylphenyl thiohydantoin derivatives have been prepared atroposelectively from the reaction of and alanine methyl ester HCl salts with -trifluoromethylphenyl isothiocyanate in the presence of triethyl amine. It was found that after purification of the crude product by simple recrystallization, the amino acid esters yielded thiohydantoins having solely axial chirality whereas the ones returned the isomers only. This result prompted us to perform sterically controlled aldol reactions on and thiohydantoin atropisomers.