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Updated: Jan 15, 2026

Synthesis of pH Dependent Pyrazole, Imidazole, and Isoindolone Dipyrrinone Fluorophores using a Claisen-Schmidt Condensation Approach
Published on: June 10, 2021
Lepidiline-Derived Imidazole-2(3H)-Thiones: (3+2)-Cycloadditions vs. Nucleophilic Additions in Reactions with
Wiktor K Poper1,2, Kamil Świątek1,2, Katarzyna Urbaniak1
1Department of Organic and Applied Chemistry, Faculty of Chemistry, University of Lodz, 91403 Łódź, Poland.
Abstract:
Two series of imidazole-2(3H)-thiones inspired by naturally occurring lepidiline alkaloids, bearing either one or two benzyl-type substituents located at the N(1)/N(3) atoms, respectively, were prepared and examined in reactions with in situ generated C-trifluoromethyl-N-aryl nitrile imines. N,N-Dibenzylated imidazole-2-thiones served exclusively as C=S dipolarophiles to afford hitherto unknown CF3-functionalized spiro [1,3,4-thiadiazole-5,2'-imidazole] derivatives formed through the (3+2)-cycloaddition pathway. In contrast, the enolizable N-monobenzylated imidazole-2-thiones provided acyclic products, i.e., hydrazonothioates, resulting from nucleophilic addition of the respective en(thio)late onto the C-termini of the 1,3-dipole. The presented results extend the scope of both fluorinated products available via trapping of the in situ generated CF3-nitrile imines as well as synthetic analogues of lepidilines. In addition, spectroscopic analysis of the obtained products and the known related systems revealed 13C NMR chemical shifts attributed to the C-(CF3) atom as useful probes to differentiate the open-chain hydrazonothioates (δ = 112-120), 2,2-diaryl/dialkyl-2,3-dihydro-1,3,4-thiadiazoles (δ = 130-145), and more strained spiro-1,3,4-thiadiazole derivatives (δ = 166-170) reported herein.
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