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Paper | Special issue | Vol 101, No. 1, 2020, pp.251-262
Published online, 25th September, 2019
DOI: 10.3987/COM-19-S(F)20
Novel Trifluoromethylated Spiro-1,3,4-thiadiazoles via [3+2]-Cycloadditions of 2,3-Diphenylcyclopropenethione with Selected in situ-Generated Nitrile Imines Derived from Trifluoroacetonitrile

Greta Utecht-Jarzyńska, Marcin Jasiński,* Kamil Świątek, Grzegorz Mlostoń, and Heinz Heimgartner*

*Department of Chemistry, University of Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland

Abstract

The in situ-generated N-aryl nitrile imines derived from trifluoroacetonitrile react efficiently with 2,3-diphenylcyclopropenethione to give spirocyclic 1,3,4-thiadiazole derivatives as products of a regio- and chemoselective (3+2)-cycloaddition in good to excellent yields. A stepwise mechanism via initial nucleophilic attack of the S-atom onto the electrophilic C-atom of the electron-deficient 1,3-dipole leading to a zwitterionic intermediate is postulated to explain these formal (3+2)-cycloaddition reactions. The presence of the CF3 group is necessary to activate the nitrile imine for the efficient trapping of the cyclopropenethione. These are the first examples of a successful reaction of this C=S dipolarophile affording 1,3,4-thiadiazoles as formal (3+2)-cycloadducts.