The highly diastereoselective synthesis of oxazolidines derived from ketones and pseudoephedrine or ephedrine

2,2-Dialkyl-3,4-dimethyl-5-phenyloxazolidines and 2-alkyl-2-aryl-3,4-dimethyl-5-phenyloxazolidines are formed with high diastereoselectivity from ketones and pseudoephedrine or ephedrine in the presence of scandium triflate and 4 A molecular sieves.