5,6,7,8-Tetrahydronaphthalen-1-amine as Precursor for Thiazolidinones and Benzothiazepinones: Synthesis and Atropisomeric Relationship

The one-pot reaction of 5,6,7,8-tetrahydronaphthalen-1-amine, mercaptoacetic acid, and arenealdehydes having strong and weak electron-withdrawing groups gave the corresponding 1,3-thiazolidin-4-ones (47-70%). When arenealdehydes bearing strong and weak electron-donating groups were used as precursors, the 1,4-benzothiazepin-2-ones were obtained (30-72%) by p-TsOH catalysis. All compounds are unknown and were characterized by GC-MS and NMR techniques, and available crystals by X-ray diffraction studies. The atropisomerism phenomenon was observed in several 1,3-thiazolidin-4-ones as confirmed by VTNMR method. The Tc was established as 332 K and the energy required for the interconversion of one atropisomer into another is around 16.8 kcal.mol(-1). Chemical quantum calculation and NOESY displayed that more stable isomer has the tetrahydronaphthalene portion below the five-ring plane. Only a small difference between isomers (-0.21 to -0.84 kcal.mol(-1)) was observed by calculated energy.