Optimized stereoselective and scalable synthesis of five-membered cyclic trans--amino acid building blocks via reductive amination

We present an optimized method for the stereoselective synthesis of five-membered alicyclic and heterocyclic trans-beta-amino acid derivatives. The process involves a reductive amination of beta-keto esters using chiral auxiliary amines, with formic acid acting as a facilitator for rapid, diastereoselective reductions under gentle conditions. Our approach notably enhances isolated yields and permits the scalable production of trans-2-aminocyclopentanecarboxylic acid (trans-ACPC), 4-aminopyrrolidine-3-carboxylic acid (trans-APC), 4-aminotetrahydrofuran-3-carboxylic acid (trans-ATFC), and 4-aminotetrahydrothiophene-3-carboxylic acid (trans-ATTC) building blocks.