An organocatalytic approach to stereoselective synthesis of 2-hydroxyazetidines and 2-hydroxypyrrolidines

A straightforward asymmetric synthesis of a new series of 2-hydroxyazetidines/2-hydroxypyrrolidines with excellent diastereoselectivity was developed via enamine catalysis using diphenylprolinol silyl ether. The Mannich-type reaction of chiral enamines with various aldimines/aziridines under mild conditions followed by intramolecular hemiaminalization affords the desired products 2-hydroxyazetidines and 2-hydroxypyrrolidines, respectively, in a one-pot operation. The scope and generality of the reaction was adequately investigated and the conditions were optimized extensively.