Synthesis of stable tetrahedral intermediates (hemiaminals) and kinetics of their conversion to thiazol-2-imines

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-C_aryl 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.

Solid-phase reactive chromatography (SPRC): a sustainable method for the synthesis of benzimidazol-diphenyl-2-imino-thiazolidine-4-ols (hemiaminals) which are active against lung cancer

Synthesis of benzimidazol-diphenyl-2-imino-thiazolidine-4-ol (hemiaminal) by column chromatography.

Axially chiral hemiaminals from nonracemic α-amino acid derivatives (thiohydantoins): Synthesis and isomer identification

Stable, nonracemic axially chiral hemiaminals (O,N-hemiacetals) have been synthesized stereoselectively from lithium aluminum hydride (LiAlH₄ ) reductions of nonracemic 5-methyl- and 5-isopropyl-3-(o-aryl)-2-thioydantoins in tetrahydrofuran (THF) at room temperature in 10 min. Predominantly S-configured hemiaminals at C-4 of the heterocyclic ring were produced from the S-configured thiohydantoins at C-5 (by 80% when the C5 substituent is methyl and by 97% when it is isopropyl). The configuration at C-5 was retained during the reduction reaction. The stereochemical outcome of the axially chiral hemiaminals resulted from their conformational preferences.

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.