We have developed a stereoselective route to the synthesis of stable i
sotope-labeled L-proline. Alkylation of (methylthio)methylidine]glycyl
}bornane-10,2-sultam with 3-chloro-iodopropane yielded e]amino}-5-chlo
ropentan-1-oyl}bornane-10,2-sultam. Cyclization to the imino acid occu
rred during the sequential removal of the alpha-amino protecting group
and the chiral auxiliary.