Dinitrosulfodienes of the 2,5-dihydrothiophene-1,1-dioxide series in reactions with nucleophiles

Reactions of dinitrosulfo-dienes of the dihydrothiophene-1,1 dioxide series, 3-methyl-4-nitro-2-(1’-nitro-1’-aryl)methylene-2,5-dihydrothiophene-1,1-dioxides, with N-and S-nucleophiles are presented. Interaction between N,N-dimethylaniline and aromatic thiols leads to the electron-transfer products. In the first case, stable molecular charge-transfer complexes are formed, while the S -nucleophiles lead to diaryl disulfides and products of reduction of the initial compounds. The reaction with the barely oxidizing sodium azide proceeds according to the second competitive route and results in the formation of products of nucleophilic vinylic substitution. Both pathways appear to be possible in the interaction with dodecanethiol, while the major process is S N Vin.


Introduction
Conjugated 1,4-dinitro-1,3-dienes can undergo competitive electron transfer reactions, nucleophilic addition and vinyl substitution 1 and are convenient substrates for studying the chemo-and regioorientation of chemical processes.

Results and Discussion
To reveal the factors influencing the chemo-and regio-orientation of the reactions of the Z,Еdinitrosulfo dienes 1 and 2 we have investigated their interaction with N-and S-nucleophiles, which are characterized by different ionization potentials.Compounds 1, 2 underwent transformations along two competitive pathways-electron transfer, and nucleophilic vinyl substitution.The exact pathway depends on the reducing properties of the reagent.
The oxidizing properties of the dinitrosulfo dienes 1, 2 were exhibited most intensively in the action of substances with low ionization potential.In this case, the electron-transfer process can stop upon formation of the charge transfer complex, or proceed further, resulting in dinitronates or products of their transformations.Thus, reactions of compounds 1, 2 with N,N-dimethylaniline led to stable crystalline molecular complexes 3, 4, in which the electron-deficient structure of the heterocyclic dinitrosulfo diene acts as an acceptor (Scheme 1).The presence of a charge-transfer band at λ max ~450 nm (ε 2000-4000) in the electron spectra of compounds 3, 4 indicates the complex nature of these substances; their binary composition is confirmed by 1 H NMR spectra and elemental analytical data.The ability of the dinitrosulfo dienes 1, 2 to form stable complexes, which is not typical for their linear analogs, is determined by the geometry of the 2,5dihydrothiophene-dioxide ring, which is close to planar. 3This is important for the formation of molecular complexes. 4,5It is worth mentioning that complexes of 2,4-dinitrothiophene-1,1dioxides with pyridine are the closest in their structure to the adducts 3, 4. 6,7 On interaction of compound 1 with easily oxidizing S-nucleophiles such as aromatic thiols (С 6 Н 5 SH, p-ClC 6 H 4 SH), electron-transfer processes proceed in a different manner.In this case, the arene-thiol is oxidized into the corresponding diaryl disulfide [diphenyl disulfide, di-(pchlorophenyl) disulfide], while the dinitrosulfo diene 1 led to the known 2-benzylidene-3-methyl-4nitro-2,5-dihydrothiophene-1,1-dioxide 5 8 (Scheme 1).
The structures of the original alkylthio-and azido-derivatives 6-11 and their configuration are determined by comparative analysis of their 1 H NMR spectra and the characteristics similar to the starting dinitrosulfo dienes 1, 2. 3 The main objective was the chemical shift value of the methyl group of the heterocycle, which is very sensitive to the chemical environment.The close values of these data in the spectra of compounds 10, 11 (2.00 ppm) and the starting Z,E-dinitrosulfo dienes 1, 2 (1.95 ppm) testify to the unchanged locations of the nitro-, methyl-, and phenyl groups, that are possible only in the case of substitution of the exocyclic nitro group and conservation of the Z,Econfiguration in the products.In the E,E-isomers of compounds 8, 9, as well as in the starting E,Edinitrosulfo dienes, the protons of the СН 3 group resonate at lower field, 2.50-2.90ppm, owing to the absence of the anisotropic shielding effect of the benzene ring. 3The essential shift of the methyl groups' protons' signals in compounds 6, 7 towards high field (1.75 ppm) proves the cis-location of the nitro-and alkylthio-groups, and hence substitution of the endocyclic nitro group in these compounds.

Conclusions
Reactions of the dinitrosulfo dienes of a series of 2,5-dihydrothiophene-1,1-dioxides with some N-and S-nucleophiles have been studied.It has been shown that the heterocyclic 1,4-dinitro-1,3dienes react with nucleophiles along two competitive pathways: electron transfer and S N Vin processes, whose ratio depends on the reducing properties of the reagents.In contrast to linear objects, the rigid dinitrosulfo dienes of the dihydrothiophene-1,1-dioxide series have a tendency to form stable molecular complexes in electron-transfer reactions.

Experimental Section
General Procedures.IR spectra were recorded on a Specord IR-75 spectrophotometer. 1 H NMR spectra were obtained on a Bruker AC-200 spectrometer at 200 MHz in CDCl 3 with HMDS as an internal standard.UV spectra were recorded on a SF-46 instrument.Column chromatography was carried out on silica L 100/250 µ.