59833-26-0Relevant articles and documents
Composes sulfures heterocycliques XCI. Syntheses et etude structurale de nitriles γ-dithiolylideniques
Catel, Jean-Marie,Mollier, Yves
, p. 113 - 124 (2007/10/02)
Our interest in compounds with delocalized ? electrons has led us to synthetise γ-dithiolylidenic nitriles on account of the strong ? electron donating character of the 1,2-dithiole and 1,3-dithiole rings.The synthesis of 4-(1,3-dithiole-2-ylidene) and 4-(1,2-dithiole-3-ylidene)-2-butenenitrile bearing a nitrile or an ethoxycarbonyl group at position 2 is carried out by reaction of the corresponding dithiolylium ions with suitable substituted 2-propenenitriles or 3-ethoxy-2-propenenitriles.In some cases the reaction of 3-(β-ethylthiostyryl)-1,2-dithiolylium ions on malononitrile also leads to 2-cyano-4-(1,2-dithiole-3-ylidene)-2-butenenitriles.By similar methods, dithiolylium ions react with cycloalkylidenemalononitriles, giving 2-(1,2-dithiole-3-ylidene) cyclopentylidenemalononitriles and cyclohexylidenemalononitriles.The 2-(1,3-dithiole-2-ylidene) cyclopentylidenemalononitriles are isolated during the reaction of tetracyanoethylene oxide with 2-(1,3-dithiole-2-ylidene) cyclopentanethiones.By suitable choice among the various methods we could obtain the γ-dithiolylidenic nitriles with yields ranging from 40 to 85percent with respect to the sulfur heterocycle.Owing to conjugation - evidenced by UV and IR, particularly by the integrated intensities of νCN bands - the 2-cyano-4-dithiolylidene-2-butenenitrile system exhibits a privileged planar conformation; furthermore, because of steric strain, the 2-cyano-4-(1,3-dithiole-2-ylidene)-2-butenenitriles have an s-trans conformation.In the case of 2-cyano-4-(1,2-dithiole-3-ylidene)-2-butenitriles, two s-trans conformations are possible.Dipole moments and NMR proton coupling constants of the 2-butene chain show that the γ-(1,2-dithiole-3-ylidenic) nitriles devoid of substituents both at position 3 of the chain and at position 4 of the heterocycle exhibit two s-trans conformations in solution, the ratios of which are evaluated by NMR.The NMR study (1H and 13C) and the determination of the dipole moment direction show that nitriles of the same type bearing a methyl at position 4 of the heterocycle or an aryl at position 3 of the chain present, because of steric strain, only one s-trans conformation in solution.The E-structure of 2-(1,2-dithiole-3-ylidene) cycloalkylidenemalononitriles has been determined by means of the dipole moments (comparison between the calculated values and the experimental values, determination of directions) and by NMR, particularly by use of shift reagents.Nevertheless, steric strain between hydrogen and all the more an alkyl at position 4 of the dithiole ring and the nearest nitrile leads to a deformation out of the plane of the heterocycle of this group.This deformation is relatively easy in the case of the 2-(1,2-dithiole-3-ylidene) cyclohexylidenemalononitriles.But with 2-(1,2-dithiole-3-ylidene) cyclopentylidenemalononitriles, the rigidity of the five-membered ring implies a torsion of the exocyclic double bond; this increases the mesoionic character of these compounds, resulting in a higher dipole moment, an increase of the intensities of νCN ...
