Stable hemiaminals from axially chiral pyridine compounds.

In this study, we have synthesized a series of 3-(pyridin-2-yl)-2-(pyridin-2-ylimino)thiazolidin-4-ol derivatives regioselectively from 2-iminothiazolidin-4-ones using LiAlH4 at room temperature. Due to the presence of the restricted rotation around the N3-Caryl single bond, the formation of M/P isomers was observed. The OH group of the hemiaminal was found to orient itself on the same side with pyridyl nitrogen during this restricted rotation to form an intramolecular hydrogen bond, which was demonstrated by the computational DFT study. This orientation presumably inhibited the occurrence of dehydration and stabilized the molecule.

Synthesis of thiazol-2-imines from the reduction of single enantiomer 2-imino-thiazolidin-4-ones followed by a spontaneous water elimination.

Chiral hemiaminals (5-8RR and 5-8SS) have been synthesized from the corresponding 2-iminothiazolidine-4-ones (1-4RR and 1-4SS) by LiAlH4 reductions stereoselectively and were then converted to single enantiomer thiazol-2-imines (9-12RR and 9-12SS) by a water elimination reaction. The kinetics of the dehydration reactions which occurred spontaneously both in the solid state and in the solution have been followed by time dependent 1 H nuclear magnetic resonance spectroscopy. The corresponding first order rate constants and free energies of activation values for the conversions have been reported.