Comparison of Large-Scale Routes to Manufacture Chiral <i>exo</i>-2-Norbornyl Thiourea

Two routes aimed at the manufacture of chiral exo-2-norbornyl thiourea (1) on large scale are described. The first approach involves five chemical steps and hinges on a classical resolution via diastereomeric salt formation. The synthesis utilizes amine 2 as the resolution handle. The second approach includes two chemical steps and a chiral chromatography of (±)-1. Despite the larger initial investment necessary to acquire the chiral stationary phase used in the chromatographic approach, the shorter reaction sequence and efficiency of the chromatographic separation make the second route a more attractive option for long-term applications.