[reaction: see text] Reaction of N-(2-phthalimidoethyl)-N-alkylisopropylamines and S(2)Cl(2) gave atropisomeric (by dynamic NMR) 4-N-(2-phthalimidoethyl)-N-alkylamino-5-chloro-1,2-dithiole-3-thiones that quantitatively cycloadded to dimethyl or diethyl acetylenedicarboxylate to give a novel class of stable thioacid chlorides, which in turn reacted with 1 or 2 equiv of secondary amines to give thioamides.

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ABSTRACT:The reaction of N-(2-phthalimidoethyl)-N-alkylisopropylamines and S 2 Cl 2 gave 4-N- (2-phthalimidoethyl)-N-alkylamino-5-chloro-1,2-dithiol-3-thiones that quantitatively cycloadded to dimethyl or diethyl acetylenedicarboxylate to give stable thioacid chlorides, which in turn reacted with one equivalent of aniline or a thiole to give thioanilides or a dithioester.Several compounds of this series showed atropisomers that were studied by a combination of dynamic NMR, simulation of the signals, conformational analysis by DFT methods, and single crystal X-ray diffraction, showing a good correlation between the theoretical calculations, the experimental values of energies and the preferred conformations in the solid state. The steric hindering of the crowded substitution at the central amine group was found to be the reason of the presence of permanent atropisomers in this series of compounds, and the cause of a unique disposition of the thioxo group at close-to-right angles with respect to the plane defined by the 1,3-