Configurational isomerization of push–pull thiazolidinone derivatives controlled by intermolecular and intramolecular RAHB: ¹H NMR dynamic investigation of concentration and temperature effects

Abstract

epoc ABSTRACT: 1 H NMR spectroscopy was used to investigate hydrogen bonding in the structurally related (Z)-and (E)-5-substituted-2-alkylidene-4-oxothiazolidines in polar and apolar solvents. The equilibrated mixtures of these typical push-pull alkenes consist of the intramolecularly H-bonded E-isomer and intermolecularly H-bonded Z-isomer in varying proportions which depend on the solvent polarity. For a representative of the series, (E)-(5-ethoxycarbonylmethyl-4-oxothiazolidin-2-ylidene)-1-phenylethanone (1), the lack of a concentration and temperature dependence of the large chemical NH shift ( 12.06 ppm) in CDCl 3 indicates strong intramolecular resonance-assisted hydrogen-bond formation (RAHB). The upfield chemical shifts of the NH proton of the (Z)-1 isomer as a function of temperature increase and the large 1 H NMR Á/ÁT value (À11.82 ppb C À1 , Z/E

Crystal Packing Modulation of the Strength of Resonance-Assisted Hydrogen Bonds and the Role of Resonance-Assisted Pseudoring Stacking in Geminal Amido Esters: Study Based on Crystallography and Theoretical Calculations

“…18,19 Also, the RAHB is used to improve the mesomorphic behavior of supramolecular liquid crystals formed from azopyridines with different linear alkyl chains 20 and control of the Diaza-Cope rearrangement 21−23 and the configurational isomerization of push−pull thiazolidinone derivatives. 24 The intramolecular RAHB was successfully studied in a wide range of systems such as β-diketone enols, 9 1,3-diketone aryl hydrazones, 25 and α-enaminones. 26 Similarly, an intermolecular RAHB was examined in β-diketone enols, 25 anti-βketoarylhydrazones, NH-pyrazoles, 27 secondary enaminones, 28 29−32 The resonanceinduced charge transfer process observed in RAHBs decreases the vibrational frequencies and shifts 1 H NMR signals downfield.…”

“…Further, the ( R )-binol-based chiral aldehydes which form RAH-bonded imines with amino acids have been developed and used as shift reagents . In addition, the same ( R )-binol-based compounds have been used in the deracemization of amino acids whereby RAHBs activate epimerization of the imine intermediates. , Compounds (5-(benzothiazol-2-yl)-4-hydroxyisophthalaldehyde and N -(2-pyridyl)-2-oxo-1-naphthylidene methyl amine) showing RAHBs have been used as chemosensors and colorimetric agents for the detection of cyanides, even in aqueous media. , Also, the RAHB is used to improve the mesomorphic behavior of supramolecular liquid crystals formed from azopyridines with different linear alkyl chains and control of the Diaza-Cope rearrangement − and the configurational isomerization of push–pull thiazolidinone derivatives …”

Discovery of Methyl (5Z)-[2-(2,4,5-Trioxopyrrolidin-3-ylidene)-4-oxo-1,3-thiazolidin-5-ylidene]acetates as Antifungal Agents against Potato Diseases

“…Compounds 1a – 1f were prepared by means of the procedure described previously. , Thioamides 2a – 2f reacted with acetylenedicarboxylate to afford 2-methylidene-1,3-thiazolidin-4-ones 1a – 1f in 45−80% yield (Figure ). Thiazolidines 1a – 1f possess a Z configuration of the exocyclic double bond in C-5. , The configuration of the exocyclic double bond in the C-2 position depends upon the solvent medium, intramolecular interactions (hydrogen bonds and weak interactions), and hindrances. ,− The 1 H NMR spectra of compounds 1a – 1f indicate that a mixture of (2 E ,5 Z )- 1a – 1f and (2 Z ,5 Z )- 1a – 1f isomers exists in DMSO- d 6 solution, in which (2 Z ,5 Z )- 1a – 1f isomers predominate as usual for related compounds. , …”

Resonance‐Assisted Hydrogen Bonding as a Driving Force in Synthesis and a Synthon in the Design of Materials

“…They have been extensively used as key intermediates in organic synthesis and as ligands in coordination chemistry, and can be synthons in bioactive natural products . β‐Enaminones are related to β‐diketones, containing the RAHB system described in Scheme . A great deal of evidence has been collected by using various spectroscopic techniques such and X‐ray analyses, showing that β‐enaminones are stabilized in the tautomeric form A .…”