Concise Synthesis of (+)‐[13C4]‐Anatoxin‐a by Dynamic Kinetic Resolution of a Cyclic Iminium Ion.

An asymmetric total synthesis of [13C4]‐anatoxin‐a ([13C4]‐1) has been developed from commercially available ethyl [13C4]‐acetoacetate ([13C4]‐15). The unique requirements associated with isotope incorporation inspired a new, robust, and highly scalable route, providing access to 0.110 g of this internal standard for use in the detection and precise quantification of anatoxin‐a in freshwater. A highlight of the synthesis is a method that leverages a cyclic iminium ion racemization to achieve dynamic kinetic resolution in an enantioselective Morita–Baylis–Hillman (MBH) cyclization. [ABSTRACT FROM AUTHOR]