Direct Access to L‐Azetidine‐2‐carboxylic Acid

A straightforward synthesis of L‐azetidine‐2‐carboxylic acid is described, leading to both orthogonally protected versions or totally deprotected L‐Aze. The starting material is a commercially available aspartic acid derivative, whose chirality is conserved. The (2‐trimethylsilyl)ethanesulfonyl protecting group (SES) acts as a leaving group on the hydroxy function and serves as an activator for the amine function, which is the key‐step of the reaction. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) A convenient and rapid synthesis of L‐azetidine‐2‐carboxylic acid is described starting from commercially available L‐aspartic acid with conservation of the chiral center. After double activation with the SES group, afour‐membered ring was formed by intramolecular N‐alkylation in quantitativeyield with the assistance of microwaveheating.